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# /sci/ - Science & Math

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Previously >>12299717

It's not that you shouldn't post a stupid answer now because a smart anon will post a smart answer later, rather, you can post a stupid answer now because a smart anon will post a smart answer later edition.

>what is /sqt/ for
Questions regarding math and science, plus related advice requests.
>where do I go for other SFW questions and (advice) requests?
>>>/wsr/ , >>>/g/sqt , >>>/diy/sqt , >>>/adv/ , etc.
https://sciencecareergeneral.neocities.org/
>books?
https://spoon.wiki/Books
https://stitz-zeager.com/
>articles?
sci-hub.st
>book recs?
https://4chan-science.fandom.com/wiki//sci/_Wiki
>help with calculus?
https://spoon.wiki/WolframAlpha
>how do I post math symbols?
https://imgur.com/MDiglsS.png
>a google search didn't return anything, is there anything else I should try before asking the question here?
>where do I look up if the question has already been asked on /sci/?
>>/sci/
https://boards.fireden.net/sci/
>how do I optimize an image losslessly?
https://trimage.org/
https://pnggauntlet.com/

>attach an image
>if a question has two or three replies, people usually assume it's already been answered
>check the Latex with the Tex button on the posting box
>if someone replies to your question with a shitpost, ignore it

Stuff:
Meme charts:https://imgur.com/a/JY6NNeL
Serious charts: https://imgur.com/a/0qDEgYt (Post any that I've missed.)
Verbitsky: https://pastebin.com/SmBc26uh
Graphing: https://www.desmos.com/
Tables, properties, material selection:
https://www.engineeringtoolbox.com/
http://www.matweb.com/

 >> Anonymous Sat Nov 7 07:37:54 2020 No.12314528 File: 794 KB, 3508x2480, __rumia_touhou_drawn_by_sh_562835932__7c2ab00125de9c96ad7bbff4fd135855.jpg [View same] [iqdb] [saucenao] [google] [report] My posts have been doing this thing where they go through but don't actually get posted, anyone know what's up?Unanswered questions:Physics questions:>>12299801>>12305199>>12306397Math questions:>>12302246>>12304017 (Yes.)>>12304098 (Just take any random one-element set.)>>12309990>>12311176Chemistry Questions:>>12306038Biology questions:>>12305677 [Technically biochem, I think.]/g/ questions:>>12307816Stupid questions:>>12304419>>12305138 [I think someone replied with spaced repetition but it got deleted.]>>12305740>>12305751>>12307550>>12308938>>12310255>>12310838>>12310881>>12312164 [B+]>>12313496>>12314325
 >> Anonymous Sat Nov 7 07:39:28 2020 No.12314533 Is OpenStax any good for pseuds who failed high school? I don't need it but after seeing it shilled on this board I checked up and hundreds of US community colleges use it.If I see a pseud post a request for books will posting openstax and hiding the thread actually help them?
 >> Anonymous Sat Nov 7 08:39:36 2020 No.12314612 Hey I'm a comp sci major but I took like 4 commerce units as as part of my degree, did intro micro, macro, intro finance and a game theory unit. Had a lot of fun with the game theory unit. Unfortunately I'm finishing my degree this year so no more study.Curious if anyone here study eco and point me towards some cool topics I could read casually/slightly more than casually? Maybe in context of tech as well would be interesting.
 >> Anonymous Sat Nov 7 08:45:51 2020 No.12314627 >>12314504So my doctor referred me for CBT after about a year and a half of stomach problems (struggling to eat, nausea, pain, panic attacks) but I'm having trouble accepting something that for me has been debilitating (lost 20kg, lost the energy to workout, ended up barely coherent due to not being able to drink water) could just be in my head, I feel the pain I feel the nausea I feel my throat closing up etc. food seems to be the trigger but so can liquid be when I'm worse than normal, type of food or volume doesn't even seem to effect the outcome it almost seems to just be how relaxed or confident I am at the time of eating. does anyone have any advice or anything?
 >> Anonymous Sat Nov 7 09:31:45 2020 No.12314701 who exactly is the paid version of wolfram for? i know there's a student version but does that mean student as in post grad maths?
 >> Anonymous Sat Nov 7 11:55:12 2020 No.12315055 >>12314701>i know there's a student version but does that mean student as in post grad maths?No, it's for undergrad students, primarily.I don't think you can even do any PhD maths in Wolfram tbqh, it barely has any functionality for things like PDEs.The paid version of Wolfram is basically just for getting increased computation time and step by step solutions.
 >> Anonymous Sat Nov 7 12:23:11 2020 No.12315127 >>12311176>>12314528PCA is quite simple in practice but its theoretical origin is definitely non-trivial (Karhunen-Loéve theorem). If you have a positive semi-definite symmetric square matrix $X$ (a variance/covariance matrix) of a zero mean discrete stochastic process $\mathbf{y}_t \in \mathbf{R}^m$ and its estimate $\hat{X}$, then you decompose the estimate matrix using its eigendecomposition $\hat{X}=W\Lambda W^{-1}$. Since $\hat{X}$ is symmetric and real, the eigenvector matrix $W \in \mathbb{R}^{m \times m}$ is composed by orthogonal eigenvectors, which can be chosen to be normalized. These normalized eigenvectors $[W_1,W_2,...,W_m]$ will compose our PCA basis. To each eigenvector is associated the eigenvalue $\lambda_j$. In general you choose the eigendecomposition such that the eigenvalues are ordered from biggest to smallest. Now if you have a sample matrix $Y \in \mathbb{R}^{N \times m}$ you obtain the principal components by transforming the matrix using the vector basis $P=YW$. The columns will be the principal components, which are orthogonal thus suitable for regression. The explained variance will depend on the eigenvalues.
 >> Anonymous Sat Nov 7 12:42:23 2020 No.12315165 >>12314612game theory is computer science + math basically. if you're interested you have zero barriers of entry and you are better prepared than economists on the subject. econ people will literally suck your genitals to have you as RA or whatever
 >> Anonymous Sat Nov 7 12:42:51 2020 No.12315166 File: 2 KB, 207x194, big fat log.png [View same] [iqdb] [saucenao] [google] [report] how can I estimate intermediate values on a logarithmic scale?
 >> Anonymous Sat Nov 7 12:57:13 2020 No.12315185 >>12315166Let $f(x)=e^{x}$ using the log transformation $\ln(f(x))=x$. The intermediate value if the log in $[a,b]$ is $(b+a)/2$ which retransfromed is $e^{(b+a)/2}$. The intermediate value of $f(x)=e^{x}$ however is, computing the mean of the function in the interval, $(e^{b}-e^{a})/(b-a)\neq e^{(b+a)/2}$. Do you think my reasoning is correct?
 >> Anonymous Sat Nov 7 13:02:19 2020 No.12315200 >>12315185bro I really dont know Im just a business major working part time as a barista
 >> Anonymous Sat Nov 7 13:14:25 2020 No.12315230 >>12315200ok. my answer is that you don't and you compute them on linear scale, then retransfrom back to log for visualization
 >> Anonymous Sat Nov 7 13:22:25 2020 No.12315245 >>12315166Every tick on the x axis is 10^x, so the point in the middle of your graph is approximately 10^1.5=30
 >> Anonymous Sat Nov 7 13:43:05 2020 No.12315318 >>12315166Do you need to literally estimate the average from a logarithmic scale graph or is the data just in logarithmic scale? If the latter, just take 10^data.
 >> Anonymous Sat Nov 7 14:38:05 2020 No.12315475 File: 16 KB, 626x188, bound questions.png [View same] [iqdb] [saucenao] [google] [report] How do I find the bounds for theta? I managed to find the bounds for the radius but I had completely forgotten how to find the bounds for $\theta$, I know that I have to take the arccos but how I reach that point is where I'm lost desu
 >> Anonymous Sat Nov 7 15:00:27 2020 No.12315532 >>12315475search for the lemniscate formula and develop from there bro.
 >> Anonymous Sat Nov 7 15:05:35 2020 No.12315546 File: 16 KB, 633x204, pic.png [View same] [iqdb] [saucenao] [google] [report] >>12315532Yaaaaaa, I got it! I actually did not know what a lemniscate is, my teachers had always just said "pedal" or "rose" or something of the sort! Now I just don't understand why the bounds for $r$ is between $0$ and $\sqrt{cos(2\theta)}$ rather than $-\sqrt{cos(2\theta)} \le r \le \sqrt{cos(2\theta)}$.
 >> Anonymous Sat Nov 7 15:12:13 2020 No.12315569 >>12315546Ever seen negative radii?
 >> Anonymous Sat Nov 7 15:13:30 2020 No.12315576 >>12315569Wtf, now that you mentioned it, I don't think I have... It becomes 'trippy' when you would have a negative radius... Thank you anon...
 >> Anonymous Sat Nov 7 17:33:10 2020 No.12316006 Where is everyone today? I miss the steady flow that we would have...
 >> Anonymous Sat Nov 7 17:43:13 2020 No.12316029 File: 121 KB, 408x430, __fujiwara_no_mokou_touhou_drawn_by_shangguan_feiying__1e0da80f44b465d9d3c649bfe0502f8a.jpg [View same] [iqdb] [saucenao] [google] [report] >>12316006Shhhhhhh, it's comfy.
 >> Anonymous Sat Nov 7 17:50:39 2020 No.12316052 >>12316006Busy talking statistics I assume
 >> Anonymous Sat Nov 7 17:56:35 2020 No.12316064 When I am writing (e.g. notes or studying), I feel like I can't write fast enough. It is a tradeoff between being legible and writing at a speed that doesn't feel slow to me. My question is, do any anons have advice for this problem, such as a shorthand method to learn or a similar thing? Some people say to invent your own shorthand but I dont really know where to start with that. Any advice appreciated
 >> Anonymous Sat Nov 7 18:14:42 2020 No.12316115 >>12316064>Some people say to invent your own shorthand but I dont really know where to start with that.For me(physics) it's basically pictures and strings of arguments. Cut the useless stuff. Knowing what's useless and what's not is the hard part and took some time to recognize.For example, in fluid dynamicsNSE, stationary-> div(rho grad(u))=div(T)Newtonian->T=-grad(p)+µ(grad(u)+grad(u)^T)Boundary conditions:->etcPay more attention to the shit the prof/book is saying than your notes. Afterwards, have a look at them and then throw them away.
 >> Anonymous Sat Nov 7 18:21:01 2020 No.12316141 >>12316115Ok thanks, I will try do this. >Afterwards, have a look at them and then throw them away.But why throw them away afteR?
 >> Anonymous Sat Nov 7 18:26:18 2020 No.12316163 >>12316141If you want to look something up it's better to just ctrl+f in a pdf or google than look through your notes.The main purpose of notes (for me at least) is to help you memorize/get familiar with it.
 >> Anonymous Sat Nov 7 18:29:10 2020 No.12316170 how do I stop thinking about money and devote myself to the field I'm passionate about instead of a field that I despise but guarantees a good salary?
 >> Anonymous Sat Nov 7 18:32:37 2020 No.12316184 >>12316163Thanks a lot
 >> Anonymous Sat Nov 7 18:40:20 2020 No.12316214 >>12316170move to 1940s soviet union and become a shock worker
 >> Anonymous Sat Nov 7 18:45:05 2020 No.12316227 >>12316170what are you passionate about anon?
 >> Anonymous Sat Nov 7 18:45:38 2020 No.12316229 Where the fuck do I find info on how you go from the divergence operator's definition to the formula for orthogonal coordinate systems. Everything I've found just leaps from the definition to the formula or talks about the divergence theorem.
 >> Anonymous Sat Nov 7 18:52:13 2020 No.12316252 >>12316227chemistryI'm in the 1st year of CS and I'm hating every moment of it but I'm not sure if transferring is a reasonable choice
 >> Anonymous Sat Nov 7 19:02:19 2020 No.12316292 >>12316252What about chemical engineering? Is only tangential to CS but... Chemical engineering is pretty low-employment too, at least that's what everyone else is saying.
 >> Anonymous Sat Nov 7 19:06:14 2020 No.12316303 >>12316292I live in a country where those jobs don't exist sadly
 >> Anonymous Sat Nov 7 19:17:34 2020 No.12316337 this is more me thinking aloud than anything but>resistance "weight lifting" with elastic bands is awkward since the resistance increases as a factor of ax^2>whereas traditional weight lifting is just a linear function of gravity, ax>presumably you could devise a way to linearize the elastic bands by dividing the equation by xI'm trying to think of what something like that would look like irl. Obviously you can't use another elastic band (or, maybe you could but it would only ever be an approximation)
 >> Anonymous Sat Nov 7 19:45:02 2020 No.12316421 Would an 8 metre fall onto water knock someone out and cause them to drown?
 >> Anonymous Sat Nov 7 19:51:14 2020 No.12316438 >>12316303what country exists without chemical engineers
 >> Anonymous Sat Nov 7 19:52:20 2020 No.12316441 >>12316421high divers routinely dive from bigger heights
 >> Anonymous Sat Nov 7 19:54:42 2020 No.12316449 >>12316438a lot of them
 >> Anonymous Sat Nov 7 20:04:23 2020 No.12316482 >>12316229IIRC https://link.springer.com/book/10.1007/978-1-4471-0597-8 had a full proof.
 >> Anonymous Sat Nov 7 20:16:49 2020 No.12316525 >>12316482>It has it detailed neatlyThanks bro>Be Physicsfag>barely pass Real Analysis>Obligatory courses shared with Mathfags over, everything else is tailored to physicists>Hopefully it'll get bet->First test is full proofs, completely fucking unrelated to what teacher has been teaching in classFor fuck's sake
 >> Anonymous Sat Nov 7 20:27:33 2020 No.12316548 >>12314504Is Pinter's Abstract Algebra good? I'd get Dummit and Foote but it's crazy expensive compared to Pinter's.
 >> Anonymous Sat Nov 7 20:30:55 2020 No.12316557 File: 2.58 MB, 2184x3276, __tokiko_touhou_drawn_by_hisha_kan_moko__56e992bcdeaa1a83213b4df4ac5705f0.jpg [View same] [iqdb] [saucenao] [google] [report] >>12316525>having to take real analysis as a physicistI'm sorry for your loss.>real analysis before vector calcAre you italian?>>12316548>is [meme book] good? I'd get [other meme book] but it's crazy expensive compared to [meme book]?Just download it on libgen and flip through the first chapter. Asking for recs makes some sense, since you'd need to flip through the first chapter of dozens of books otherwise, but asking if a single book is good doesn't.
 >> Anonymous Sat Nov 7 20:33:49 2020 No.12316564 >>12316557I took vector calc before analysis, but when we did divergence we just got the straight formula for Cartesian, no definition, and later the direct formula for spherical and cilindrical coordinates.
 >> Anonymous Sat Nov 7 20:40:59 2020 No.12316582 >>12316564Ah, I see.
 >> Anonymous Sat Nov 7 21:08:03 2020 No.12316636 >>12316252I would say make the switch. I am a third year engineering student and know friends who only did it for the income potential, and they are miserable. They wish they switched or dropped out earlier.
 >> Anonymous Sat Nov 7 21:40:24 2020 No.12316731 Why are voltages in a parallel circuit the same whereas voltage in a series circuit is split?????? I can't comprehend this.
 >> Anonymous Sat Nov 7 22:06:08 2020 No.12316790 >>12316731Alright, think of current as water falling downwards.Think of a parallel circuit as the water having multiple paths downwards. At the same height, regardless of path, the water is bound to have the same gravitational potential energy.Think of a series circuit as a series of tubes in a single path leading the water downwards. As the water goes down the tubes, so does its gravitational potential energy.
 >> Anonymous Sat Nov 7 23:34:08 2020 No.12316957 >>12316337The force from an elastic band or a (typical) spring is linear; gravity is constant. The stored energy (integral of force w.r.t. distance) increases in proportion to x^2 or x respectively.You can get constant-force springs, which are typically a roll of stainless steel. If you try to unroll them, they'll try to return to their original shape, and the force is roughly constant. You can somewhat linearise the force generated from a conventional spring by incorporating it into some form of linkage; probably the best-known example is an anglepoise desk lamp. As the joint angle increases, the relative motion changes from axial to tangential, counteracting the way that the force increases with extension.
 >> Anonymous Sat Nov 7 23:44:06 2020 No.12316973 >>12316482>>12316557Meant to reply to this, but fell asleep briefly. This is one of the worst vector/multi calc books I've ever looked at. I hope to God neither you nor anyone else in this thread learns the subject from this.A list of books that will not treat you like a retarded child:Multivariable Mathematics: Linear Algebra, Multivariable Calculus, and Manifolds (Shifrin)Vector Calculus, Linear Algebra, and Differential Forms: A Unified Approach (Hubbard & Hubbard)Introduction to Calculus & Analysis Vol II (Courant and John)Mathematical Analysis Vol II (Zorich)Advanced Calculus of Several Variables (Edwards)Advanced Calculus (Buck)Advanced Calculus (Loomis & Sternberg)Advanced Calculus, A Geometric Approach (Callahan)Multidimensional Analysis (Duistermaat & Kolk)Analysis on Manifolds (Munkres)Calculus on Manifolds (Spivak)
 >> Anonymous Sat Nov 7 23:48:35 2020 No.12316981 >>12314504with advanced enough genetic engineering tech can you create real life furries?
 >> Anonymous Sat Nov 7 23:52:25 2020 No.12316988 If I flip a coin until I get either heads or tails 100 times (doesnt have to be in a row) how many times will I have flipped a coin on average? I simulated this and got 188, but dont know how to calculate an answer.
 >> Anonymous Sun Nov 8 00:47:57 2020 No.12317087 >>12316988Off the top of my head I'm 90% sure that's a negative-binomial distribution and it's some gross thing with a million slightly different parameterisations.
 >> Anonymous Sun Nov 8 01:02:13 2020 No.12317109 >>12316988The probability of getting exactly H heads from N trials is C(N,H)/2^N where C(n,r) is the binomial coefficient C(n,r)=n!/n!(n-r)!. So the probability of getting 100 heads OR 100 tails is twice that. For N<100, the probability of getting 100 heads or 100 tails is zero. For N>100, you need the probability of getting 100 heads/tails given that you didn't already have 100 heads/tails after N-1 trials. IOW, the probability of having 99 heads after N-1 trials AND getting a head on the Nth OR having 99 tails after N-1 trials AND getting a tail on the Nth: P(N)=C(N-1,99)/2^(N-1). Sum N*P(N) for 100<=N<200 to get the expected value.I get 303277905920577398875311583052735687729539680821475899692011200 / 1606938044258990275541962092341162602522202993782792835301376 ~= 188.73030419814873.
 >> Anonymous Sun Nov 8 01:25:47 2020 No.12317151 >>12317109For reasons I can't be bothered to explore right now, the sum simplifies to 200*(2^200-2*C(199,99))/2^200 = 200*(1-C(199,99)/2^199)
 >> Anonymous Sun Nov 8 03:24:22 2020 No.12317395 I ONLY HAVE $800 LEFT IN MY BANK ACCOUNT AND NEED A JOB BY THE END OF NEXT MONTH, EXCEPT I'M A FUCKING AUTIST WHO CAN'T DRIVE AND AM FREAKING OUT BECAUSE MY INTERVIEW FOR WAL MART IS NEXT TUESDAY AND THERE'S LIKE 500 OTHER PEOPLE LOOKING FOR JOBS AS WELL.ALSO MY STOMACH ISSUE HAS LASTED 2 WEEKS, GETTING BLOOD DRAWN ON MONDAY, WHICH MEANS I HAVE TO GO INTO THE INTERVIEW UNDER PAINWHAT FUCKING DO  >> Anonymous Sun Nov 8 03:26:36 2020 No.12317398 >>12317395The stomach issue compounds my anxiety by not letting me sleep and waking me up in the middle of the night. I had like 3 hours of sleep today and have to try and sleep in a chair to remove as much pressure from my mid section as possible.  >> Anonymous Sun Nov 8 08:26:07 2020 No.12317874 File: 27 KB, 679x179, Capture.png [View same] [iqdb] [saucenao] [google] [report] why is the future like this  >> Anonymous Sun Nov 8 09:42:00 2020 No.12318004 File: 1.86 MB, 2424x2145, Geological_time_spiral.png [View same] [iqdb] [saucenao] [google] [report] >>12314504Just updated with minor stuff. All inputs are welcome, we have a long way to go. The old sites are in deep bit rot so there is a lot of updating to be done.  >> Anonymous Sun Nov 8 10:08:46 2020 No.12318040 I asked this in the previous thread but I still can't work out the problem.I need to compute $\operatorname{Aut} (\mathbb{Z} \times \mathbb{Z})$. Consider $e_1 = (1,0) , e_2 = (0,1)$. If $f$ is an automorphism of $\mathbb{Z} \times \mathbb{Z}$ then surely $f(e_1), f(e_2)$ are linearly independent over $\mathbb{R}$. So this is a necessary condition, but not sufficient. I'm not sure how to proceed...  >> Anonymous Sun Nov 8 10:14:29 2020 No.12318049 >>12318040Do you know Aut(Z)?  >> Anonymous Sun Nov 8 10:17:29 2020 No.12318055 >>12318040I've already spoonfed you on the previous thread. Two by two matrices, integer coefficients, invertible. Hence, $GL(2, \mathbb{Z})$.>does it have some funny description thoNo.https://groupprops.subwiki.org/wiki/General_linear_group:GL%282,Z%29  >> Anonymous Sun Nov 8 11:55:05 2020 No.12318260 >>12314504I'm new to math, assume n are natural numbers, and we have the set {1,2...,2n}.How is it possible to have 1 and 2 in there? Shouldn't it be {2,4...,2n}?What does the rest of the set look like?Pls don't laugh, I'm a tard.  >> Anonymous Sun Nov 8 11:58:49 2020 No.12318268 >>12318260This is the set of natural numbers from 1 to some even number.  >> Anonymous Sun Nov 8 12:02:37 2020 No.12318280 >>12318268So it's; {1,2,6,8,10,...,2n} ?Thanks anon. I was confused.  >> Anonymous Sun Nov 8 12:03:25 2020 No.12318282 >>12318280No, it's {1,2,3,4,...,2n}. 2n just means the last number will be some even number (because 2 times any integer is even).  >> Anonymous Sun Nov 8 12:05:25 2020 No.12318289 >>12318282Ah, I get it. Tyty anon.  >> Anonymous Sun Nov 8 12:42:36 2020 No.12318391 >>12318289>>12318280>>12318268>>12318260Last question. What set should I think of when people talk about n+1 Integers?  >> Anonymous Sun Nov 8 12:49:11 2020 No.12318419 If I have a relation consisting of (1,1) based on a set {1,2,3} is it symmetrical? I feel retarded af but I just can't find an answer anywhere.Or does there need to be a y that isn't x for it to be symmetrical?  >> Anonymous Sun Nov 8 13:01:37 2020 No.12318467 >>12314504Should I even bother going for a maths degree if I'm already 24? I'm already paying for the universities with my taxes here, so I might as well take advantage of it. What other degrees are /sci/ approved? I'm currently a code monkey btw  >> Anonymous Sun Nov 8 13:06:37 2020 No.12318487 >>12318419In the same vein, can any relation consisting of only, say {(1,1),(1,2),(2,1),(2,2)} be transitive, as that by definition requires an x,y and z or can x y and z be equal and the relation still be transitive?  >> Anonymous Sun Nov 8 13:17:22 2020 No.12318522 >>12318467>a maths degreeHow do you wish to use it? As part of your software career?I did a BSc and then PhD in physics. Interesting and varied subject but you probably need a PhD to get the interesting jobs.  >> Anonymous Sun Nov 8 13:23:38 2020 No.12318539 >/scg/ isnt upill give remilia friend about 30 minutes before i either make it myself or just post my question here  >> Anonymous Sun Nov 8 13:27:37 2020 No.12318552 >>12318539>>/scg/ isnt upIt was mentioned in an earlier thread it was killed by the mods, and the OP got banned. Just the pasta remains.>ill give remilia friend about 30 minutes before i either make it myself or just post my question hereJust ask here.  >> Anonymous Sun Nov 8 13:28:41 2020 No.12318557 >>12318467normally id only recommend it if it's what you want to do, but with cs background there's definitely also career benefits. math teaches you how to think and problem solve in a way which will open up your options for doing more interesting research-like software / tech jobs than typical code monkey ones.  >> Anonymous Sun Nov 8 13:35:14 2020 No.12318569 >>12318539That section of the pasta has already been removed since /scg/ is apparently not going to be a thing (thanks a bunch jannie), just ask here.  >> Anonymous Sun Nov 8 13:36:16 2020 No.12318573 >>12318569Removed in the previous edition, actually.  >> Anonymous Sun Nov 8 13:42:03 2020 No.12318590 >>12318552>>12318569>it was killed by the modsthats really shitty. i wish there was some form of retaliation for crappy behavior like thatanyway, my question: have any of you heard of REU programs? im currently EE undergrad (burgerstan) thats set to graduate spring 2022 at the earliest, probably later. ive been begging my profs for research, and one of them hinted that they might have something for me in the fall of next year, which is cool but i was hoping for something earlier. the other day, i unfortunately found myself in the company of a bunch of physics majors and they were talking about REUs, which sounded like a summer research internship at some uni (a bunch of unis have programs like these). are these memes? is it "real" research experience? should i just try to get "real" research experience instead? ive never heard of these programs before, and i was a bit skeptical. undergrad research is so ubiquitous in physics that i was wondering if REUs were the kind of research for people who couldnt get "real" research, but again i dont know shit (could you tell?)  >> Anonymous Sun Nov 8 13:59:24 2020 No.12318631 fuck fuck fuck I have to turn in a paper tomorrow and I just realized that I don't have any evidence/source for one of my claims in it, becausse it was my own idea.It's the following formula to describe how to calculate the distance to a spacecraft based on it's response times to radio signals.[eqn] s = \frac{(t_{total}-t_{reaction})\cdot c}{2} [\eqn]It obviously isn't that complicated, $t_{reaction}[\math] is the time the spacecraft electronics need to respond, but the problem is that I can't find any source on this. I found this https://www.qrg.northwestern.edu/projects/vss/docs/Navigation/1-how-do-we-know-location.html which is intended to educate kids and https://www.engineering.com/AdvancedManufacturing/ArticleID/12390/Quality-Basics-How-Does-3D-Laser-Scanning-Work.aspx which is not about spaceflight at all.Can you please give me some search terms real quick? I need to sleep as soon as possible but as I said I have to turn it in tomorrow and haven't found anything usable yet. thanks frens  >> Anonymous Sun Nov 8 14:00:29 2020 No.12318636 fuck fuck fuck I have to turn in a paper tomorrow and I just realized that I don't have any evidence/source for one of my claims in it, becausse it was my own idea.It's the following formula to describe how to calculate the distance to a spacecraft based on it's response times to radio signals.[eqn] s = \frac{(t_{total}-t_{reaction})\cdot c}{2} [/eqn]It obviously isn't that complicated, [math] t_{reaction}$ is the time the spacecraft electronics need to respond, but the problem is that I can't find any source on this. I found this https://www.qrg.northwestern.edu/projects/vss/docs/Navigation/1-how-do-we-know-location.html which is intended to educate kids and https://www.engineering.com/AdvancedManufacturing/ArticleID/12390/Quality-Basics-How-Does-3D-Laser-Scanning-Work.aspx which is not about spaceflight at all.Can you please give me some search terms real quick? I need to sleep as soon as possible but as I said I have to turn it in tomorrow and haven't found anything usable yet. thanks frens  >> Anonymous Sun Nov 8 14:02:19 2020 No.12318638 >>12318636Obviously that only works exactly if the spacecraft is still but works as a good approximation overall, you don't need to cite anything.  >> Anonymous Sun Nov 8 14:04:48 2020 No.12318649 >>12318638>you don't need to cite anythingnot sure about that, if that formula can be found somewhere on the internet it is basically plagiarizing it, right? Sorry if that is stupid but it is the first kind of paper with a "scientific" approach I have to write  >> Anonymous Sun Nov 8 14:13:29 2020 No.12318676 >>12318522>How do you wish to use it? As part of your software career?Probably, but I'm fairly open in that regard. I like the idea of getting a mathematics degree since it's relevant in so many fields.>you probably need a PhD to get the interesting jobsI wouldn't be opposed to spending another ten years or so in school as long as I can afford the cost of living, so it's something I might be interested in as well. If I'm doing well enough, of course. Thanks for the advice.>>12318557I'd still do it mostly for myself tbqh, I could probably get into a management position in my firm without a degree, that just not really something I want.Would you guys recommend doing pure maths or something like compmaths or applied maths?  >> Anonymous Sun Nov 8 14:14:49 2020 No.12318681 >>12318419>>12318487pls respond  >> Anonymous Sun Nov 8 14:24:56 2020 No.12318716 >>12318649>not sure about that, if that formula can be found somewhere on the internet it is basically plagiarizing it, right?Usually it depends on your audience.But with this it's shorter to prove yourself than cite anything  >> Anonymous Sun Nov 8 14:26:30 2020 No.12318721 >>12318590https://nsf.gov/crssprgm/reu/list_result.jsp?unitid=10006REUs are real and legit. Some people may argue how useful the research that comes out of it, but I would say that it gives you a taste of what research is like.  >> Anonymous Sun Nov 8 14:27:57 2020 No.12318727 >>12318716thank you. Guess I'll just use that one url I posted as a citation at the end of the chapter, that way I could both argue that I got some basic information out of that webpage and that I came up with the formula myself in the very unlikely case that my teacher even checks my sources.  >> Anonymous Sun Nov 8 14:34:50 2020 No.12318748 >>12318727Or you make a drawing with earth, distance s, spacecraft and write 2s/c+t_reaction=t_total -> your formula for small speeds, instead of quoting a website for children or qrg.northwestern.edu  >> Anonymous Sun Nov 8 14:40:11 2020 No.12318756 >>12318748honestly I don't have the time to make a proper drawing right now. I made a shitty diagram with TikZ yesterday and it took me way too long so I don't really want to go through that again. But good idea, thanks  >> Anonymous Sun Nov 8 14:41:43 2020 No.12318758 >>12318721thanks anonwhen applying to graduate programs, would REUs be as good as other, more "intimate" research, you think? i think that youre supposed to get a rec letter from the guy you did research under, but i dont think that would be possible with REU, would it?  >> Anonymous Sun Nov 8 14:47:33 2020 No.12318780 >>12318569>>12318573The pasta remains up on Neocities and has been updated: https://sciencecareergeneral.neocities.org/  >> Anonymous Sun Nov 8 14:49:41 2020 No.12318789 >>12318636>Can you please give me some search terms real quick?Essentially it is the same process as for radar. The beam goes out, is reflected back so the path length is twice the distance.  >> Anonymous Sun Nov 8 14:51:15 2020 No.12318792 >>12318780I mean the "Go to /scg/ for carreer advice instead of asking here" section of the pasta.It's still in >>12283246 , but in >>12299717 it was already removed.  >> Anonymous Sun Nov 8 14:53:13 2020 No.12318797 >>12316973Best books for probability and statistics?  >> Anonymous Sun Nov 8 14:56:00 2020 No.12318810 >>12318676>>How do you wish to use it? As part of your software career?>Probably, but I'm fairly open in that regard. I like the idea of getting a mathematics degree since it's relevant in so many fields.Mathematics cover a lot fields, some rather esoteric and not applicable in the foreseeable future. From my own time doing Applied Physics I remember we had a fair bit of maths and also statistics, so there are alternative sources for the knowledge. Obviously this was then a selection with a focus on applied maths.>>you probably need a PhD to get the interesting jobs>I wouldn't be opposed to spending another ten years or so in school as long as I can afford the cost of living, so it's something I might be interested in as well. If I'm doing well enough, of course. Thanks for the advice.You are welcome. A PhD does not have to take too many years, in the UK is is now closer to 3 years.>I'd still do it mostly for myself tbqh, I could probably get into a management position in my firm without a degree, that just not really something I want.>Would you guys recommend doing pure maths or something like compmaths or applied maths?I would recommend applied maths since it will give you a fallback position. Also it will not be too offputting to employers who can have a lot of opinions on things they know nothing about.  >> Anonymous Sun Nov 8 15:17:26 2020 No.12318916 >>12318758different burger phd anon here>are REUs better than local researchin general, no. the benefit of research at your school is that you can get deeper into the work until you're actually somehow connected to relevant things.however, REUs are still good. if you have no other option (due to availability at your school) then REUs are amazing. if you get one with a good group in your field, it can even be better than spending a summer at your home school. >can you get a rec letter from an REUyes, absolutely. just make sure you make contact with your REU professor while you're there so they have things to say.in general, you shouldn't ask for a rec letter for something that was over two years ago though. so I wouldn't ask for a letter from an REU prof if you did the work after your sophomore year, but after junior year would be fine.  >> Anonymous Sun Nov 8 15:45:06 2020 No.12319037 >>12318916thank you very much, anon. i have no fuckin clue what im doing so this kind of advice really helps  >> Anonymous Sun Nov 8 15:50:45 2020 No.12319068 >>12319037get in contact with phds at your uni. the whole process is more complicated than it needs to be but in general there are clear answers that people in the field know. it's just that these aren't readily available on public places  >> Anonymous Sun Nov 8 15:56:20 2020 No.12319101 >>12319068my uni doesnt have a PhD program for physics or EE, embarrassingly enough  >> Anonymous Sun Nov 8 17:06:41 2020 No.12319334 I have to find the work needed to lift 50kg 20 meters with a rope that is 2kg per meter.9.8∫2002x+50dxIs this the correct setup?  >> Anonymous Sun Nov 8 17:08:13 2020 No.12319339 >>12319334$9.8 \displaystyle\int_0^{20} 2x + 50 \, dx$  >> Anonymous Sun Nov 8 17:12:21 2020 No.12319353 >>12319339Do the units work out?  >> Anonymous Sun Nov 8 17:34:51 2020 No.12319420 >>12319353I just slapped a J on that bitch and sat down with a beer.  >> Anonymous Sun Nov 8 17:40:24 2020 No.12319439 >>12319353Yes  >> Anonymous Sun Nov 8 17:40:54 2020 No.12319441 >>12319420kek  >> Anonymous Sun Nov 8 18:33:18 2020 No.12319603 File: 81 KB, 985x1024, 1604818819468.jpg [View same] [iqdb] [saucenao] [google] [report] I don't think Im going to get into the CS program. What should I study instead?I want to double major applied math with something else.  >> Anonymous Sun Nov 8 18:44:22 2020 No.12319636 File: 7 KB, 380x51, set theory.png [View same] [iqdb] [saucenao] [google] [report] Please bros somebody explain how to prove these equations to meWhile I am completely new to these notations, I understand what they're implying, I just can't make sense of it  >> Anonymous Sun Nov 8 19:10:30 2020 No.12319715 File: 47 KB, 400x400, Untitled.png [View same] [iqdb] [saucenao] [google] [report] >>12319636Just draw the sets to make things clearer. I'll do (1) for you. Left is M except the intersection of N and P. Right is M except N and then M except P. Both right circles have the intersection of N and P grayed out, so their union is equivalent to the left circle.  >> Anonymous Sun Nov 8 19:13:04 2020 No.12319732 >>12319715I understand it visually, I put it into wolfram and the venn diagram was easy to understand.I'm just not sure how to change up the equations to show this, I doubt I can just draw the sets to prove their equality.  >> Anonymous Sun Nov 8 19:32:02 2020 No.12319810 >>12319732It's just a property you're supposed to know (De Morgan's laws). As far as proof goes, I think proofwiki is fairly transparent: https://proofwiki.org/wiki/De_Morgan%27s_Laws_(Set_Theory)/Set_Difference/Difference_with_Intersection.  >> Anonymous Sun Nov 8 19:45:23 2020 No.12319854 File: 36 KB, 610x140, q5.2.png [View same] [iqdb] [saucenao] [google] [report] Anons help where the fuck do I start with this question. Its from Davidson and Donsigs Real analysis and applications, sec 5.1 question M. The corollary in question just says "Every linear map A from Rn to Rm is Lipschitz, andtherefore is continuous".  >> Anonymous Sun Nov 8 19:50:13 2020 No.12319872 >>12319854The proof of the corollary proceeds by constructing a constant and showing that it works.Repeat the process of construction to answer a).  >> Anonymous Sun Nov 8 20:02:29 2020 No.12319911 >>12319872Ohhh thanks so much I did not get what it was asking. So would I just get 16^0.5=4 then? Or am i still misunderstanding  >> Anonymous Sun Nov 8 20:04:15 2020 No.12319920 >>12319911I haven't read the proof of the corollary, does 16 come from the sum of the modulos of all the entries?Because it's actually 8 in that case, but otherwise it looks correct.  >> Anonymous Sun Nov 8 20:07:57 2020 No.12319936 >>12319920*sums of the squares of the modulos of the entries.*actually 4 in that case.  >> Anonymous Sun Nov 8 20:10:27 2020 No.12319947 >>12319636Here is a quick attempt feel free to debate it(1)Let x be in M/(N and P). The complement of M/(N and P) is (N and P). This implies that x is in N and not in P, or in P and not in N, or in neither. If x in is in N, it belongs to the complement of P, that is x in M/P. If x is in P, it belongs to the complement of N, that is M/N. if x is in neither, it belongs to both M/N and M/P. Therefore x is in (M/N)U(M/P).Let x be in (M/N)U(M/P). Then it either belongs to the complement of N or to the complement of P or both. If it belongs to the complement of N, then it does not belong to P. If it belongs to the complement of P, then it does not belong to N. If it belongs to both complements, then it does not belong to neither N nor P. x will never be both in N and P. Therefore x is in M/(N and P).M/(N and P) = (M/N)U(M/P)(2)Ler x be in M/(NUP). x does not belong to neither P nor N, then it belongs to the intersection of their complements. Therefore x is in (M/N)and(M/P).Let x be in (M/N)and(M/P). If x is in (M/N), it also belongs to (M/P), so it is not in P nor in N. If x is in (M/P), it also belongs to (M/N), so it is not in P nor it is in N. So x in never in P and never in N, therefore it belongs to the complement of (NUP). Therefore x is in M/(NUP).M/(NUP) = (M/N)and(M/P)  >> Anonymous Sun Nov 8 20:17:30 2020 No.12319977 >>12319947>Let x be in (M/N)U(M/P). Then it either belongs to the complement of N or to the complement of P or both. If it belongs to the complement of N, then it does not belong to P. If it belongs to the complement of P, then it does not belong to N. If it belongs to both complements, then it does not belong to neither N nor P. x will never be both in N and P. Therefore x is in M/(N and P).This one is wrong sorry, it's late here. Try to do it yourself. Anyway to prove these statements you have to prove the equality by going in one direction and then the other  >> Anonymous Sun Nov 8 20:18:22 2020 No.12319978 >>12319936the proof is using i think its called the euclidean norm of the matrix, the root of the sum of the squares of each entry. but i just realized i dropped the 1/2 so i think id be getting 2 actually  >> Anonymous Sun Nov 8 20:21:20 2020 No.12319987 >>12319978>i think its called the euclidean norm of the matrixThe Frobenius norm.> but i just realized i dropped the 1/2 so i think id be getting 2 actually...yeah, that's what I was talking about earlier.  >> Anonymous Sun Nov 8 20:23:49 2020 No.12319994 >>12319810>>12319947Thank you friends  >> Anonymous Sun Nov 8 20:32:03 2020 No.12320008 >>12319987Thanks for the help. i get how to show that norm of x is equal to norm of ax, but how then do i use the orthonormal basis formed by the columns of A to find the best Lipschitz constant of 1?  >> Anonymous Sun Nov 8 20:38:31 2020 No.12320018 >>12320008It's kinda dumb, you should solve it on your own tbqh.Well.$\|Ax - Ax_0 \| = \|A(x-x_0) \| = \|x-x_0\|$, hence $\|Ax - Ax_0 \| \leq \|x-x_0\|$  >> Anonymous Mon Nov 9 02:20:47 2020 No.12321096 File: 43 KB, 750x766, 1602866384265.jpg [View same] [iqdb] [saucenao] [google] [report] Can someone recommend me a good book on catalysis? Looks like there are so many with varying reviews.  >> Anonymous Mon Nov 9 02:22:05 2020 No.12321102 File: 14 KB, 472x121, fuckoff.png [View same] [iqdb] [saucenao] [google] [report] Please tell me there's a less obtuse method to getting the probability of rolling 2 or more 2s with 7 dice than this, this seems like it'd chew up a retarded amount of time on an exam compared to just a calculator function..  >> Anonymous Mon Nov 9 02:49:32 2020 No.12321154 >>12321102Sorry friend it's all just counting up ways you do and don't get it.  >> Q (You) Mon Nov 9 02:54:01 2020 No.12321162 File: 159 KB, 438x1569, 8D28676C-DA7F-446F-9FC4-2E8813772F79.jpg [View same] [iqdb] [saucenao] [google] [report]  >> Anonymous Mon Nov 9 05:06:52 2020 No.12321463 Bump.  >> Anonymous Mon Nov 9 06:26:15 2020 No.12321632 >>12318916>REUsSeems relevant for the csg page. Anything similar in other countries?  >> Anonymous Mon Nov 9 06:27:59 2020 No.12321636 Is taking the mean of absolutes the same as absolute of means, i.e. mean(abs(x)) = abs(mean(x)) where x is a dataset.  >> Anonymous Mon Nov 9 06:29:19 2020 No.12321640 >>12321636Try it with 1 and -1  >> Anonymous Mon Nov 9 06:35:31 2020 No.12321654 >>12321640thanks t. retard, that was kind of obvious  >> Anonymous Mon Nov 9 07:31:57 2020 No.12321769 >>12315127>PCA is quite simple in practice but its theoretical origin is definitely non-trivial>Karhunen-LoéveThat's one of many ways to understand PCA. Another one is purely geometric (fitting a hyperellipsoid to your data). In the end, they all mean the same but the approach they offer differs in difficulty.  >> Anonymous Mon Nov 9 08:28:15 2020 No.12321874 >>12321654by the way, this is why variance can exist  >> Anonymous Mon Nov 9 09:16:12 2020 No.12322009 >>12321769'fitting an hyperellipsoid' is an ass pull that data people use. KL is the proper framework to derive PCA  >> Anonymous Mon Nov 9 09:29:35 2020 No.12322042 File: 128 KB, 392x224, vyVAfa3WLU.png [View same] [iqdb] [saucenao] [google] [report] Hey I've been trying to understand circuits analysis but I can't seem to make progress. How would you proceed here to find$R_{A}\$ value ? I feel fucking dumb I did fine and all the previous "hard" courses but I can't get my head around this.
 >> Anonymous Mon Nov 9 09:59:50 2020 No.12322101 File: 708 KB, 1889x987, zcfsfswef.png [View same] [iqdb] [saucenao] [google] [report] How come in related rates problems involving triangles. (take the ladder falling against a wall problem) after we have found the rate at which it is falling and how much distance is on the ground the sides no longer add up to the original length of the ladder (hypotenuse) https://www.youtube.com/watch?v=ps-r4nti5Gothe problem at 31:16 is what I am talking aboutbeforehand the original triangle has sides 13,5, and 12but after 1 minute the new lengths are13,12.2, and 9im sure its something simple Im just missing but any explanation as to why would be great
 >> Anonymous Mon Nov 9 10:23:17 2020 No.12322167 >>12321096what kind of catalysis?
 >> Anonymous Mon Nov 9 10:28:25 2020 No.12322182 >>12319334What happens to the rest of the rope? Depending upon the setup, it might act as a counterweight.
 >> Anonymous Mon Nov 9 10:32:08 2020 No.12322190 >>12322101You must have got the new lengths wrong. Did you mix one of them up with its derivative?
 >> Anonymous Mon Nov 9 10:32:52 2020 No.12322191 >>12322042What's the question? Find what given what? The most general approach is to construct a system of linear equations using KCL and KVL then solve it.
 >> Anonymous Mon Nov 9 10:58:51 2020 No.12322268 >>12322101To find the new lengths just use pythagorean theorem because you already have 2 sides (9 and 13). Or how did you find that 12.2 length?
 >> Anonymous Mon Nov 9 11:11:44 2020 No.12322310 >>12322009I understand it's your favorite approach, but it's not the only one. Orthogonal projections to minimize Euclidean distance are another. And again, ultimately they all mean the same.
 >> Anonymous Mon Nov 9 11:37:43 2020 No.12322379 >>1232226812.2 is from the 5+7.2. since the ladder is moving 7.2 ft from the wall a minute and the 9 is from the 12-3 since its falling down the wall at 3ft a minute.those are just the lengths it should have after 1 minute has passed for height and length?
 >> Anonymous Mon Nov 9 12:55:25 2020 No.12322636 >>12322101The velocities aren't constant. At least, they can't both be constant[1]. So you can't take the velocities at an instant and extrapolate the positions at some point in the future from them. x(t+δt) ~= x(t)+δt*x'(t) only holds if δt is small.[1] Differentiating x^2+y^2=l^2 gives 2x.x'+2y.y'=0 => x'/y'=-y/x, i.e. the ratio of the velocities is proportional to the slope, and the slope is constantly changing. So if x' is constant, y' can't be and vice versa.
 >> Anonymous Mon Nov 9 13:13:11 2020 No.12322707 File: 35 KB, 556x291, Untitled.png [View same] [iqdb] [saucenao] [google] [report] you guys know those constants An and Bn that are found using An = half sine expansion of f(x) etc...?how do I find An if u(x,0) = f(x) is 3 different functions?I tried 3 seperate integrals (3h/L from 0 to L/3), (h from L/3 to 2L/3) and (-3h/L from 2L/3 to L) but I wasnt sure what to do with them afterI added them together but it wasnt the correct answerpls halp
 >> Anonymous Mon Nov 9 13:56:16 2020 No.12322880 >>12322707wait those are just the slopes im retarded
 >> Anonymous Mon Nov 9 14:08:08 2020 No.12322935 >>12316170The truth is that if you love what you're doing you're more likely to be good at it (and thus achieve a higher salary) than anything else. Think 5th percentile chemist vs 50th percentile CS graduate salary.
 >> Anonymous Mon Nov 9 15:34:15 2020 No.12323261 File: 41 KB, 374x374, 1563452925053.jpg [View same] [iqdb] [saucenao] [google] [report] If I store my soda bottles upside down, will they lose gas slower or faster?
 >> Anonymous Mon Nov 9 15:35:29 2020 No.12323264 >>12323261Higher surface area, should be faster
 >> Anonymous Mon Nov 9 15:39:00 2020 No.12323276 File: 76 KB, 288x402, 1562342312794.jpg [View same] [iqdb] [saucenao] [google] [report] >>12323264But the cap is down so where does the gas escape to?
 >> Anonymous Mon Nov 9 15:43:39 2020 No.12323292 >>12323276Gas is compressibleI was using the assumption you'd shake your soda or something, because if both phases are in equilibrium obviously nothing would happen
 >> Anonymous Mon Nov 9 15:53:26 2020 No.12323340 File: 502 KB, 2000x3000, __nazrin_touhou_drawn_by_kozakura_dictionary__7c6b56dc658af7b16e1e9f23704cc69d.jpg [View same] [iqdb] [saucenao] [google] [report] >/big/ has actually consistently been in the catalog when I open it for a couple months nowIs /big/ a serious general or just random shitposting? Do I add it to the pasta?
 >> Anonymous Mon Nov 9 16:02:58 2020 No.12323384 Undergraduate in Mathematics here, is it worth it to strive to research Representation Theory or should I try and learn something else?
 >> Anonymous Mon Nov 9 16:28:20 2020 No.12323541 What are the units of the second moment of a random variable? Suppose I have a probability distribution with mean $m$. The expected value of my random variable then has the same units as the following sum: [eqn]E(X) = \sum_x xp(x) = m.[/eqn] Suppose then that my probability distribution is random (Poisson), so that the second moment has a well-defined form. In particular, this is [eqn]E(X^2) = \sum_x x^2p(x) = m^2 - m.[/eqn]But this doesn't make much sense to me... since $m^2$ and $m$ don't share units.. am I a retard? can someone enlighten me as to this seemingly obvious contradiction? What are the units of $E(X^2)$? Any help is appreciated, this is seriously holding up any progress I am making on a project
 >> Anonymous Mon Nov 9 16:36:12 2020 No.12323587 >>12323541Var(X) = E(X^2)-E(X)^2 = m^2 - m^2 + m = m
 >> Anonymous Mon Nov 9 16:51:42 2020 No.12323689 >>12323541> What are the units of the second moment of a random variable?Normalised or unnormalised? Normalised moments are unitless (you're effectively dealing with Z scores); the units of an unnormalised nth moment are U^n where U is the units of the random variable.> Suppose then that my probability distribution is random (Poisson), so that the second moment has a well-defined form. The Poisson distribution applies to a discrete unitless variable, specifically a count. It gives you the probability of something happening k times in a given interval. The mean and variance of a Poisson distribution are both equal to the parameter λ (the variance is the second central moment).
 >> Anonymous Mon Nov 9 16:51:51 2020 No.12323691 If I have a factory that has two different processes for producing light bulbs and I want to find out whether lightbulbs produced by Process A have a greater probability of failure than lightbulbs produced by process B what kind of statistical test should I do? I know the total numbers of lightbulbs produced by each process abd total numbers of failures for each process. out of Y lightbulbs produced by process A , X lightbulbs have failed. And out of Q lightbulbs produced by process B , P have failed.X/Y and P/Q are both very small fractions that are in the region of 0.00001 to 0.000001 if that makes a difference.
 >> Anonymous Mon Nov 9 16:52:40 2020 No.12323698 >>12323587Right but this is conditional on X being randomly distributed. Made me think tho. So E(X^2) shares units with E(X)^2? Still not making much sense from my second line - we subtract $m$ from $m^2$
 >> Anonymous Mon Nov 9 16:54:35 2020 No.12323705 >>12323689>The Poisson distribution applies to a discrete unitless variable, specifically a countBut the expected value is a sum over $xp(x)$ for all x, which has units, no? The data is not normalized.
 >> Anonymous Mon Nov 9 17:08:45 2020 No.12323752 >>12323698>So E(X^2) shares units with E(X)^2?You have to remember that E(X^2)=Var(X) if E(X)=0. The variance in general is the centralized second moment E((X-m)^2).So if you don't centralize it, it makes sense that it contains information about the mean and the variance
 >> Anonymous Mon Nov 9 17:11:52 2020 No.12323770 >>12323705The random variable is a count. A Poisson distribution isn't applicable to anything else. A count is a unitless quantity, thus so are the expected value and all moments.
 >> Anonymous Mon Nov 9 17:30:52 2020 No.12323832 >>12323770ohhhhhh, now I see what you mean. The expected value, although it may have physical meaning (e.g. deaths per day or parasites per host), is simply a count and therefore unitless
 >> Anonymous Mon Nov 9 18:25:23 2020 No.12324010 File: 2 KB, 510x79, Untitled.png [View same] [iqdb] [saucenao] [google] [report] how
 >> Anonymous Mon Nov 9 18:30:38 2020 No.12324032 File: 116 KB, 375x445, __touhou_drawn_by_shangguan_feiying__34e1bb99bdbf2a4c5fd7e2ed92a8079d.jpg [View same] [iqdb] [saucenao] [google] [report] >>12324010Exhaustion.>seriously?Yes, seriously.
 >> Anonymous Mon Nov 9 18:32:00 2020 No.12324039 >>12324032>Exhaustionw-what?
 >> Anonymous Mon Nov 9 18:36:05 2020 No.12324050   Just a test:\sin(\frac{n\pi}{3})Also, is Catalysis: An Integrated Textbook for Students a good book?
 >> Anonymous Mon Nov 9 18:37:38 2020 No.12324058 >>12324050gotta put it between (math) and (/math) but use square brackets instead of round
 >> Anonymous Mon Nov 9 18:38:50 2020 No.12324065 >>12324058Ahhhh thanks, like this?:$\sin(\frac{n\pi}{3})$
 >> Anonymous Mon Nov 9 18:39:34 2020 No.12324067 File: 2.39 MB, 720x720, 1602463704228.gif [View same] [iqdb] [saucenao] [google] [report] >>12324065there you go!
 >> Anonymous Mon Nov 9 18:52:22 2020 No.12324113 >>12324010$\sin(\frac{2n\pi}{3})$ is + for n = 1, - for n = 2, - for n = 3, + for n = 4, + for n = 5, and so on. $\sin(\frac{n\pi}{3})$ is positive for n = 1, n = 2, negative for n = 3, n = 4, and so on. So, $\sin(\frac{n\pi}{3})$ is obviously the same as $(1)(\sin(\frac{2n\pi}{3}))$, but $\sin(\frac{n\pi}{3})$ must be offset by $-(-1)^{n}$ to match $\sin(\frac{2n\pi}{3})$. $|\sin(\frac{n\pi}{3})| = |\sin(\frac{2n\pi}{3})|$, but the signs won't match without that $-(-1)^{n}$. $(-(-1)^{n})(\sin(\frac{n\pi}{3}))$ is positive for n = 1, negative for n = 2, negative for n = 3, and negative for n = 4, but positive again for n = 5 and so on. The $-(-1)^{n}$ is just something that must be determined with the signs of each term. Hopefully that made sense and I didn't fuck anything up in this tiny text window.>>12324067thanks anon
 >> Anonymous Mon Nov 9 18:52:39 2020 No.12324114 >>12324039$\sin (x + 2 \pi) = \sin x$, so you only actually need to prove that for $n = 0, \ldots, 5$.>can't you do it with the sine sum formula or whateverMaybe, but you'll probably still have to exhaust somewhere.
 >> Anonymous Mon Nov 9 18:53:41 2020 No.12324120 >>12324113I did mess it up, damn, meant to say its positive for n = 4 in that last line.
 >> Anonymous Mon Nov 9 18:55:04 2020 No.12324126 File: 30 KB, 646x335, bounds for v.png [View same] [iqdb] [saucenao] [google] [report] How did they figure out the bounds for (v) which is just the radius? I don't understand what they mean by "Transform each limit... into a limit for v using z = 3-3v^2...... into the equation and solve for v. When z = 0, v is 1"
 >> Anonymous Mon Nov 9 18:59:53 2020 No.12324136 >>12324113>>12324114thank you!!
 >> Anonymous Mon Nov 9 19:01:02 2020 No.12324142 File: 44 KB, 112x112, fren_headrubs.gif [View same] [iqdb] [saucenao] [google] [report] >>12324136no prob
 >> Anonymous Mon Nov 9 19:37:08 2020 No.12324268 why is the catalog full of frogs today? do you think it is just one retard spamming them?
 >> Anonymous Mon Nov 9 19:47:56 2020 No.12324308 Where do I start?
 >> Anonymous Mon Nov 9 20:33:13 2020 No.12324409 >>12324268Frogposters are stupid.
 >> Anonymous Mon Nov 9 20:48:47 2020 No.12324453 >>12323832>>12323541bumping pls
 >> Anonymous Mon Nov 9 20:55:18 2020 No.12324476 >>12323541I usually discard unit information when dealing with random variables, but the definition of the second moment is[eqn]E[X]^2=\int_{X}x^2d\mu[/eqn]if $x$ has units, then since the integral is linear the second moment will have squared units. This makes sense since the standard deviation then has the same units as the random variable, and intuitively this is consistent.
 >> Anonymous Mon Nov 9 20:56:23 2020 No.12324482 >>12324476sorry its $E[X^2]$ fucked up the parentheses
 >> Anonymous Mon Nov 9 20:57:49 2020 No.12324489 >>12324476>I usually discard unit information when dealing with random variablessame, but my ODE system uses them and I'm trying to nondimensionalize it, which is causing some problems if you could imagine. May just scrap the nondimensionalization. Thanks for the help friend
 >> Anonymous Mon Nov 9 21:04:57 2020 No.12324526 >>12324489Can't just take a standard value and divide all your values by that amount in units so its all dimensionless?
 >> Anonymous Mon Nov 9 21:36:46 2020 No.12324671 >>12324526Not really sure what you mean. Introducing a variable into the ODE system to simplify units would need justification. If you're talking about the nondimensionalization bit, then yes that what nondimensionalization is. However, I'm finding that the expressions concerning moments of a random variable do not behave nicely when I try to nondimensionalize them. Specifically, a parameter in my model will have different units depending on where you find it in the overall system. It's quite annoying.
 >> Anonymous Mon Nov 9 22:42:35 2020 No.12324848 How do I free myself from calculators? I have found myself to become dependent.
 >> Anonymous Mon Nov 9 22:44:34 2020 No.12324853 >>12324848Either you practise your arithmetic or you stop doing things that need calculating.
 >> Anonymous Mon Nov 9 22:46:54 2020 No.12324865 File: 27 KB, 112x112, 1604090001919.gif [View same] [iqdb] [saucenao] [google] [report] >>12324853Fair enough. Guess I'll start, idk why I thought there was any other way.
 >> Anonymous Tue Nov 10 02:02:22 2020 No.12325296 Why does 1/R_p = 1/R_1 + 1/R_2 = R_1+R_2/R_1R_2, R_p = R_1R_2/R_1+R_2 work when trying to figure out the equivalent resistance of 2 paralleled resistor?
 >> Anonymous Tue Nov 10 02:13:12 2020 No.12325316 >>12325296V1=V2=VpI1=V1/R1 = Vp/R1I2=V2/R2 = Vp/R2Ip=I1+I2 = Vp/R1+Vp/R2Rp=Vp/Ip => 1/Rp=Ip/Vp = (Vp/R1+Vp/R2)/Vp = 1/R1+1/R2
 >> Anonymous Tue Nov 10 02:19:45 2020 No.12325331 File: 5 KB, 284x261, circuit.png [View same] [iqdb] [saucenao] [google] [report] >>12325296I1 is the current through the top branch, I2 is the current through the second branch, by Kirchoff's current law, the total current I = I1 + I2. By Kirchoff's voltage law, the voltage across the top resistor is the same as the voltage across the second resistor (walk around the loop to sum voltages to zero).So, V = I1 R1, V = I2 R2. Therefore I = V/R1 + V/R2, so I/V = 1/R1 + 1/R2, since I/V = 1/Rp (total resistance), then 1/Rp = 1/R1 + 1/R2.
 >> Anonymous Tue Nov 10 03:36:35 2020 No.12325443 >>12325296The key is that the voltage across both resistors has to be the same but the current differs.Vbatt = Vbranc1 = Vbranch2Vbranch1 = R1 x I1 etc.
 >> Anonymous Tue Nov 10 05:01:27 2020 No.12325599 >>12324126>z=3-3v^2z=0: 3=3v^2 v=1z=3:3=3-3v^2v=0Like this?
 >> Anonymous Tue Nov 10 05:05:20 2020 No.12325605 File: 1.93 MB, 300x369, The mountain looked at e.gif [View same] [iqdb] [saucenao] [google] [report] >>12314504What's the optimal defensive wall you could build, think wall around a very small village, and how many years would that optimal wall last? Didn't think /k/ was the right board for this.
 >> Anonymous Tue Nov 10 06:19:58 2020 No.12325716 File: 397 KB, 1247x799, 1561835163291.jpg [View same] [iqdb] [saucenao] [google] [report] >>12325605How about pic. related?I have seen berms around a local hill fort dating back to about year 600, still standing.
 >> Anonymous Tue Nov 10 06:23:06 2020 No.12325722 >>12325716True, I bet if you used something to stabilize the dirt like the sheeting layers they do for highway construction it could be pretty steep.
 >> Anonymous Tue Nov 10 08:21:50 2020 No.12326061 >>12324526>Not really sure what you mean. Introducing a variable into the ODE system to simplify units would need justification. If you're talking about the nondimensionalization bit, then yes that what nondimensionalization is. However, I'm finding that the expressions concerning moments of a random variable do not behave nicely when I try to nondimensionalize them. Specifically, a parameter in my model will have different units depending on where you find it in the overall system. It's quite annoying.Could there be an implict conversion constant? Like a factor of 1 unit per otherunit somewhere?
 >> Anonymous Tue Nov 10 09:07:59 2020 No.12326184 Can diamond dust be used in a dust explosion?
 >> Anonymous Tue Nov 10 09:27:39 2020 No.12326243 any medfags here? do you have an immunity of sorts after overcoming an illness, i know some people with the rona that I have contacted over the last few days, however I was recently sick myself and I have no symptoms whatsoever so is it possible that I also got rona but am currently immune to it or am I trippin?
 >> Anonymous Tue Nov 10 09:28:56 2020 No.12326249 >>12326243should add that I have no idea if my illness was rona or not, I contracted it from a different place a couple days prior
 >> Anonymous Tue Nov 10 10:15:04 2020 No.12326363 File: 70 KB, 720x540, naughty number 9.jpg [View same] [iqdb] [saucenao] [google] [report] I was watching pic related out of nostalgia the other day, and the penny product principle interested me. The penny product being numbers divisible by 9 have individual digits whose sum are also factors of 9. Is there any writing that details why this is?
 >> Anonymous Tue Nov 10 10:25:36 2020 No.12326398 >>12326363For digits a, b, and c in number nn = 100*a + 10*b + cn= 99 *a + 9 *b + (a+b+c)n= 9 ( 11*a + b) + (a +b+c)The first part is clearly divisible by 9The second part is divisible by 9 by the premise of the questionThus n is divisible by 9.
 >> Anonymous Tue Nov 10 11:12:37 2020 No.12326538 Guys I wanna skip college algebraHow can i learn college algebra in a week?
 >> Anonymous Tue Nov 10 11:18:29 2020 No.12326563 >>12326538Hit your head against a wall10 times should be enough
 >> Anonymous Tue Nov 10 11:56:55 2020 No.12326732 >>1232636310^n≡1 (mod 9) for all n. So[eqn]\sum_n d_n 10^n \equiv \sum_n d_n {\pmod 9}[/eqn]IOW, the number itself (which is the sum of each digit multiplied by the corresponding power of 10) is only divisible by 9 (i.e. congruent to zero modulo 9) if the sum of the digits is divisible by 9.Note that also 10^n≡1 (mod 3) for all n, so a number is divisible by 3 iff the sum of its digits is divisible by 3.
 >> Anonymous Tue Nov 10 12:17:22 2020 No.12326814 File: 1.33 MB, 1969x2894, __nazrin_touhou_drawn_by_prat_rat__fb29e1b6da1a1d9ce1cb4e371203ee19.jpg [View same] [iqdb] [saucenao] [google] [report] >>12323384I don't know all that much rep theory or about how rep theory research is doing nowadays, but Yukarifag once claimed rep theory is a field in physics.>>12324308The beginning.
 >> Anonymous Tue Nov 10 13:54:12 2020 No.12327142 >>12326563dont listen to this smart ass, anonive never seen anyone do it in less than 20
 >> Anonymous Tue Nov 10 14:07:25 2020 No.12327206 File: 32 KB, 533x369, Untitled.png [View same] [iqdb] [saucenao] [google] [report] can anyone explain what Im doing wrong here?will post what I tried after this post
 >> Anonymous Tue Nov 10 14:08:34 2020 No.12327215 File: 1.80 MB, 3200x4261, IMG_20201110_140626_1.jpg [View same] [iqdb] [saucenao] [google] [report] >>12327206what I triedsorry about the handwriting, Im a noob that can't latex
 >> Anonymous Tue Nov 10 14:20:20 2020 No.12327266 Any recommendations for some concise physics notes covering (at least) an intro physics w/ calc course (mechanics (kinematics, energy/work, friction etc)somethinkg like pauls online notes or just a 30 page or less pdf would be awesome
 >> Anonymous Tue Nov 10 14:31:46 2020 No.12327319 >>12327215What happens to sin(n pi/2) when n is even?
 >> Anonymous Tue Nov 10 14:32:48 2020 No.12327321 File: 157 KB, 339x686, 1601683695126.png [View same] [iqdb] [saucenao] [google] [report] My ejaculate was cold yesterday.How does that work?
 >> Anonymous Tue Nov 10 14:41:16 2020 No.12327351 >>12327321Is it not supposed to be cold/warm? Anon, I think that is more in line with your environment's temperature than anything else
 >> Anonymous Tue Nov 10 14:41:58 2020 No.12327356 >>12327321>>12327351my cum is always piping hot, not sure wtf wrong with u guys
 >> Anonymous Tue Nov 10 14:42:42 2020 No.12327362 >>12327356How the fuck is your cum piping hot? Can you give a temperature aproximate?
 >> Anonymous Tue Nov 10 14:45:55 2020 No.12327375 >>12327319its 0 but I don't really see how that's applicable here
 >> Anonymous Tue Nov 10 14:50:58 2020 No.12327391 >>12327375n must be oddso n=2k-1 and sin(k pi/2) = (-1)^k-1Then your solution is the same as the one in the problem
 >> Anonymous Tue Nov 10 14:57:40 2020 No.12327411 File: 22 KB, 280x413, 1588206302401.jpg [View same] [iqdb] [saucenao] [google] [report] anybody know who he is
 >> Anonymous Tue Nov 10 15:10:35 2020 No.12327470 given $\vec{F} = 2i - 3j$ and $\vec{d} = -4i$, why is the work done by force F considered negative? I understand the math checks out (i.e, $F\cdot d$ or $|F||d|cos\phi$, where $\phi$ is the angle between d and F, but I disagree. I think the work would be positive, because F is ultimately shoving d in the direction of the positive x-axis. Clearly my intuition is wrong, but if the resulant vector between F and d displaces d positively, why is the work considered negative?
 >> Anonymous Tue Nov 10 15:13:46 2020 No.12327480 >>12327470Because you get energy out of it, instead of having to put energy into the system
 >> Anonymous Tue Nov 10 15:14:48 2020 No.12327487 >>12327470>in the direction of the positive x-axisthis is not true though? $F \cdot d = -8 \hat{x}$
 >> Anonymous Tue Nov 10 15:16:41 2020 No.12327498 >>12327487>>12327480Well I'm not sure what I'm misunderstanding, F has a positive x-component, so being that d is headed in the negative x direction, I would think the work F is trying to do would push d in the positive x direction, so it's positive work being done. Again I know I'm wrong, I'd just like to identify where I'm going wrong.
 >> Anonymous Tue Nov 10 15:19:11 2020 No.12327509 >>12327391oh you're rightthank you so much
 >> Anonymous Tue Nov 10 15:19:29 2020 No.12327511 >>12327487>>12327470>>12327498oh I see. you're applying a force to the right of something over a distance of 4 units to the left. that means that whatever you're working on is moving to the left and you're slowing it down by pushing to the right. you're thus using work to counteract the kinetic energyWork-energy theorem: $W=K_f-K_i$ the work done on a system is equal to the change in kinetic energy (assuming no dissipative forces or change in potential).Negative work just means your initial kinetic energy was larger than your final kinetic energy
 >> Anonymous Tue Nov 10 15:22:41 2020 No.12327528 >>12327511>Negative work just means your initial kinetic energy was larger than your final kinetic energythanks so much!
 >> Anonymous Tue Nov 10 15:45:59 2020 No.12327602 File: 231 KB, 1151x2048, __hong_meiling_touhou_drawn_by_risui_suzu_rks__a4ad42b5cff12b798dadb0a42ca8ce4b.jpg [View same] [iqdb] [saucenao] [google] [report] >>12327411Daniel Dennet.
 >> Anonymous Tue Nov 10 15:46:03 2020 No.12327604 File: 79 KB, 824x940, 2020-11-10-153348_824x940_scrot.png [View same] [iqdb] [saucenao] [google] [report] a question from my digital design book asks:>(a) Find a minimum two-level NOR gate circuit to implement F1 and F2, using as many common gates as possible$F_1\left(a,b,c,d\right)=\sum m\left(1,2,4,5,6,8,10,12,14\right)$$F_2\left(a,b,c,d\right)=\sum m\left(2,4,6,8,10,11,12,14,15\right)$>(b) Realize F1 and F2 using a PLAI'm able to do (a) just fine, but looking at the solutions manual, I have absolutely no clue how they managed to get those "product terms" in the pic that they used for the PLA table, considering the final NOR-NOR expressions are$F_1\left(A,B,C,D\right)=\left(\left(A+B+C+D\right)'+\left(A'+B+D'\right)'+\left(C'+D'\right)'\right)'$$F_2\left(A,B,C,D\right)=\left(\left(A+B+C+D\right)'+\left(A+C'+D'\right)'+\left(C'+D'\right)'\right)'$what are those product terms? Converting to SoP doesn't give me those terms either (unless I fucked it up)
 >> Anonymous Tue Nov 10 16:06:00 2020 No.12327680 File: 3.18 MB, 1966x3496, __remilia_scarlet_touhou_drawn_by_yukito_dreamrider__6721d871bee3788a803d523af60a2990.jpg [View same] [iqdb] [saucenao] [google] [report] Scientifically speaking, why do I think this Remilia is cute and absolute garbage at the same time?
 >> Anonymous Tue Nov 10 16:10:53 2020 No.12327718 >>12327604>(unless I fucked it up)I think you did
 >> Anonymous Tue Nov 10 16:11:14 2020 No.12327722 File: 49 KB, 615x102, q5.2.png [View same] [iqdb] [saucenao] [google] [report] What is c) is asking here. Is it asking for a sequence that is cauchy wrt both metrics but only convergent wrt one metric? In that case can I just use X={1/n for natural n} and my sequence just be X, then the usual metric is not convergent in X wrt usual metric since 0 is not in X but it is convergent in X wrt discrete metric since 1 is in X. Am I think of this right or am i misunderstanding and its asking something other than a sequence that is cauchy in both but convergent in one?
 >> Anonymous Tue Nov 10 16:15:53 2020 No.12327742 >>12327722I would say they want a sequence which is cauchy in one space but not cauchy in other space
 >> Anonymous Tue Nov 10 16:17:42 2020 No.12327751 >>12327722oh and those spaces need to be topologically equivalent, that's the whole point. your X and discrete X are not homeomorphic.
 >> Anonymous Tue Nov 10 16:23:49 2020 No.12327782 >>12327722That is the right example, but your reasoning is all wonky. Thet want a sequence that is cauchy in one space but not in the other, and yours is cauchy in the usual metric but not the discrete one, so that works. It's not convergent in either but it doesn't need to be.
 >> Anonymous Tue Nov 10 16:24:05 2020 No.12327783 >>12327751X={1/n for n in naturals} equipped with either usual or discrete metric is topologically discrete i thought?
 >> Anonymous Tue Nov 10 16:25:29 2020 No.12327791 Do changes in altitude, such as when an airplane lands, change the need to urinate?
 >> Anonymous Tue Nov 10 16:27:52 2020 No.12327799 File: 4 KB, 430x58, calculus.png [View same] [iqdb] [saucenao] [google] [report] Help me bros, I'm supposed to prove this equation is true no matter the truth value.I just don't get how ¬B and B can occur at the same time, it makes no sense to me.
 >> Anonymous Tue Nov 10 16:28:13 2020 No.12327800 >>12327782ohhhh i get it thanks for the answer. i think i retardedly thought that the discrete metric being equal to 1 somehow meant the sequence was converging to 1 but i see the retardation in that now and realize that actually the discrete metric always being equal to 1 means that the sequence isnt even cauchy. thanks
 >> Anonymous Tue Nov 10 16:31:23 2020 No.12327813 >>12327799OH MY GOD I'M A FUCKING IDIOTExactly because that can't be true it's AFuck
 >> Anonymous Tue Nov 10 16:32:31 2020 No.12327817 >>12327722Yes, you are on the right track. They are asking to have one space X with two metrics d_1,d_2, that are topologically equivalent, then find a sequence which is Cauchy in one metric and not Cauchy in the other. And of course your example is correct.
 >> Anonymous Tue Nov 10 17:37:15 2020 No.12328046 so when is Yellowstone going off?
 >> Anonymous Tue Nov 10 18:32:35 2020 No.12328201 What is this theorem called? $F_1,...,F_n\models{G} \iff F_1\land...\land{F_n}\implies{G}$
 >> Anonymous Tue Nov 10 18:36:46 2020 No.12328211 >>12325316>>12325331>>12325443Thanks guys
 >> Anonymous Tue Nov 10 19:36:01 2020 No.12328435 >>12314627First of all, if it is "all in your head", that doesn't make it any less real. Second of all, it can't hurt to try CBT. Might help with other issues in life as well. Give it a shot, and good luck man. Try not to worry too much, we're all slowly marching towards the afterlife anyway.
 >> Anonymous Tue Nov 10 19:46:51 2020 No.12328473 >>12314627how the fuck is cock and ball torture gonna help?
 >> Anonymous Tue Nov 10 19:47:44 2020 No.12328477 >>12328473if you don't like cbt there dbt (dick and ball torture)
 >> Anonymous Tue Nov 10 19:58:13 2020 No.12328513 >>12314627Current body thread?
 >> Anonymous Tue Nov 10 20:00:36 2020 No.12328515 >>12328201That's not the definition?
 >> Anonymous Tue Nov 10 20:04:45 2020 No.12328523 Hey guys, /pol/tard here, I'm curious about why eugenics is no longer thought of as a way to improve the species. Would you have some input or links that I can look through?
 >> Anonymous Tue Nov 10 20:09:04 2020 No.12328535 >>12327799That's the essence of Proof by Contradiction.
 >> Anonymous Tue Nov 10 20:15:53 2020 No.12328558 >>12328523eugenics was ditched because it was a 'nazi thing' so since WW2 everyone thinks it's either pseudoscience or too immoral to study. However humans select breeding mates by eugenics (literally) so it's just a big hypocrisy. It will soon come back
 >> Anonymous Tue Nov 10 20:39:40 2020 No.12328627 File: 89 KB, 1177x495, modulacion-fm-onda-cuadrada.jpg [View same] [iqdb] [saucenao] [google] [report] >>12314504does anyone know a good FM generating circuit i can use for a simulation in multisim? need for hw but cant find a good one, did one with a 555 but it modulates using a square carrier which is useless for me.im looking to do something like pic rel
 >> Anonymous Tue Nov 10 20:42:46 2020 No.12328637 >>12328558>humans select breeding mates by eugenicsthis was only true before the industrial revolution (or if you want to be radical, agriculture)
 >> Anonymous Tue Nov 10 20:50:12 2020 No.12328654 >>12328637no, everyone has some standards about their potential partner. 'having standards' is eugenics, it's totally natural. people can't accept it though so it's swept under the rug.
 >> Anonymous Tue Nov 10 20:51:58 2020 No.12328659 >>12328201Completeness?
 >> Anonymous Tue Nov 10 20:55:54 2020 No.12328671 >>12328523Because we don't understand the eventual consequences well enough. Selectively eliminating genes from the pool inherently reduces genetic diversity, so you would want to be quite certain that those genes are unambiguously "bad" before you do that.So you have a combination of the genes which eugenicists want to eliminate are those which are only possessed by "others" coupled with the fact that the people doing the selecting are those who would consider this to be an important task. Which is a recipe for creating a "master race" of insecure pencil-dicks.
 >> Anonymous Tue Nov 10 21:01:27 2020 No.12328685 What's a good chess app/widget that lets you "play both sides"? I want to dink around with openings. Is this embedded in certain popular apps?
 >> Anonymous Tue Nov 10 21:14:03 2020 No.12328724 >>12328654yes, and the standards have been lowered
 >> Anonymous Tue Nov 10 23:40:03 2020 No.12329058 >>12328558this>>12328724If you're an NPC who thinks having kids with a 27yo roastie is perfectly fine, then yes.
 >> Anonymous Tue Nov 10 23:40:16 2020 No.12329059 >>12328523>I'm curious about why eugenics is no longer thought of as a way to improve the species.jews want easy cattle not strong humans who are self reliant and competent enough to overthrow their yoke
 >> Anonymous Wed Nov 11 00:56:27 2020 No.12329287 File: 27 KB, 800x724, iq chart.png [View same] [iqdb] [saucenao] [google] [report] Does anyone have the meme version of this chart where the line extends out to like 800 IQ?
 >> Anonymous Wed Nov 11 01:49:10 2020 No.12329386 I'm guessing >90% of /sci/ voted for Biden, correct?
 >> Anonymous Wed Nov 11 01:50:41 2020 No.12329392 >>12329287this picture looks like a meme already
 >> Anonymous Wed Nov 11 01:53:22 2020 No.12329395 How many liters of milk does a baby have to drink to double its weight?
 >> Anonymous Wed Nov 11 01:54:24 2020 No.12329397 >>12329386We have lots of non American posters here
 >> Anonymous Wed Nov 11 01:59:30 2020 No.12329412 >>12329386What retard would vote for biden?
 >> Anonymous Wed Nov 11 02:00:15 2020 No.12329416 >>12329386How insecure are you to ask /sqt/ to affirm your own voting preferences?
 >> Anonymous Wed Nov 11 02:01:17 2020 No.12329420 >>12329386>votingishygddt
 >> Anonymous Wed Nov 11 02:37:33 2020 No.12329471 >>12314504Im trying to teach myself math/physics and I have not found a satisfactory example of this simple problem I want to set up:Imagine a tank with any volume you like and any gas/pressure you like. If I open a valve on the side of this gas tank how should I model this relative to TIME? I'm pretty sure this is not a pressure equalization problem because everything I have looked up says its flow. I think where I am confused is starting with an initial pressure/amount of gas, pressure inside the tank (and outside) should be what determines the flow through the valve, but the flow is going to decrease as pressure drops in the tank to equalize with the outside environment. So its just pipe flow with an initial condition, right? I'm guessing its going to be a partial derivative, but I expected a problem like this would be common and I have not found an example that matches my expectations at all.
 >> Anonymous Wed Nov 11 02:41:21 2020 No.12329473 >>12329471Force at the leak = water pressure (pgz? Don’t remember) So:F(t) = pgz(t) = ma(t) and then derive flow by integrating the accel?
 >> Anonymous Wed Nov 11 02:54:11 2020 No.12329490 >>12329473 Sorry, I should be more clear, lets say this is a pressure problem and not a gravity problem. So i could have an air tank on my space craft and I am releasing air from my air tank into my room. Everything is in freefall so no gravity at work in this example.
 >> Anonymous Wed Nov 11 02:56:56 2020 No.12329493
 >> Anonymous Wed Nov 11 03:05:55 2020 No.12329513 >>12329471Volume flow is given by Hagen-PoiseuillePressure can then be calculated with the new volume and an EoS of your choosing. Probably as an van der waals gas.
 >> Anonymous Wed Nov 11 03:15:12 2020 No.12329529 >>12329416I'm Brazilian
 >> Anonymous Wed Nov 11 06:24:44 2020 No.12329771 >>12328523It was tried by Sparta and you can see today it didn't work out for them.
 >> Anonymous Wed Nov 11 06:26:34 2020 No.12329776 >>12329397The people entrusted with counting the votes.
 >> Anonymous Wed Nov 11 07:36:31 2020 No.12329905 In set notation, is it different to say:>{x + y = 10 | (x >0) and (y > 0)}compared to>{(x >0) and (y > 0) | x + y = 10}aka does the order of the "such that" matter?
 >> Anonymous Wed Nov 11 11:04:00 2020 No.12330333 File: 74 KB, 812x854, __yakumo_yukari_touhou_drawn_by_rin_falcon__0375219611d385bf41b141dfe85beaa2.jpg [View same] [iqdb] [saucenao] [google] [report] >>12329386/sci/ is a Kanye board.We hear Yeezy. We wear Yeezy. We groove Yeezy.We vote for genuine christian candidates with authentic moral fiber, such as Yeezy, instead of mr. Joseph "I need the thot vote so I'm pro-abortion" Biden or mr. Donald "didn't build the fucking wall" Trump.>>12329905Technically speaking, you write down$\{ (x, y) \in \mathbb{R}^2 : x > 0 \land y > 0 \land x + y = 10 \}$, but swapping the order doesn't matter, no.
 >> Anonymous Wed Nov 11 11:17:24 2020 No.12330370 Is anyone familiar with cosmic strings? I am looking for a purely topological treatment that does not rely on condensed matter physics. I have found mention of the fundamental group being used for their definition, but no full definition or further references. Topological treatments of general topogical defects are welcome as well.
 >> Anonymous Wed Nov 11 11:18:41 2020 No.12330374 In what paper it is stated that the polar ice biomes are calle polar desserts?
 >> Anonymous Wed Nov 11 11:26:30 2020 No.12330392 >>12330333ISYUKARIFAGBACK?
 >> Anonymous Wed Nov 11 11:31:24 2020 No.12330400 >>12330392...no, I just posted a Yukari.It's not even the kind of post he'd make, calm down lad.
 >> Anonymous Wed Nov 11 11:33:25 2020 No.12330408 File: 56 KB, 620x850, 1466033994248.jpg [View same] [iqdb] [saucenao] [google] [report] >>12330400I miss yukarifag but good thing ur still here jiji
 >> Anonymous Wed Nov 11 11:46:37 2020 No.12330435 >>12330408how do I become good at math
 >> Anonymous Wed Nov 11 11:47:44 2020 No.12330437 >>12320727You need to start with the standard results of the field $\mathbb{R}$, then work on the theorems of the ordered field $\mathbb{R}$ and the basic theorems of the normed field $\mathbb{C}$ and the number-theoretic results for the embedded $\mathbb{Z}$ and $\mathbb{Q}$ in either real or complex number system. After this you can start proving the standard results of naive set theory and linear algebra, but do not avoid the elements of real analysis.
 >> Anonymous Wed Nov 11 11:49:12 2020 No.12330443 File: 450 KB, 1280x720, P vs C.png [View same] [iqdb] [saucenao] [google] [report] Princeton or Caltech for Physics?
 >> Anonymous Wed Nov 11 11:59:15 2020 No.12330470 Why aren't threads like >>12329942 common in /sci/?
 >> Anonymous Wed Nov 11 12:04:14 2020 No.12330484 >>12330470We're only slightly homosexual
 >> Anonymous Wed Nov 11 12:16:34 2020 No.12330526 >>12330484Makes sense.
 >> Anonymous Wed Nov 11 12:23:52 2020 No.12330552 >>12330484huhh, thats gay
 >> Anonymous Wed Nov 11 12:47:29 2020 No.12330626 >>12330443undergrad or grad?I'm at caltech right now for grad. I think for undergrad I'd recommend princeton unless you want to be surrounded by a ton of autistic kids. although princeton is in the literal middle of nowhere.grad depends on the field you're in, I'd say caltech is stronger in most disciplines that it offers. but princeton offers more.
 >> Anonymous Wed Nov 11 12:55:54 2020 No.12330655 >>12330435I think you asked the wrong person, but my take on it is to "grind grind grind." That's how I passed my math classes.
 >> Anonymous Wed Nov 11 13:39:31 2020 No.12330799 File: 116 KB, 485x312, 1603236048045.png [View same] [iqdb] [saucenao] [google] [report] >>12330655oh, ok
 >> Anonymous Wed Nov 11 13:43:18 2020 No.12330819 Could anyone recommend me good reading sources for Swarm Intelligence? Or the link to the book's PDF?In other words, is Particle Swarm Optimization a meme or the real deal?
 >> Anonymous Wed Nov 11 14:25:01 2020 No.12331016 Where did I go wrong here?Spring and a box on a frictionless plane inclined at 30 degrees. Box is 12kg, initially at rest, spring has a constant Hooke's law thingy of 13,500N/m.The block begins sliding down the slope and compresses the spring 0.055M, how far from the stopping point was it's rest point?The right thing to do is mgd = 1/2kx^2, solve for d. But what I did was find the force the box applied to the spring to compress it as much as it did (13,500N/m = x/0.055m -> x = 742.5N), then found the height needed to make that happen (mgcos(theta)d = 742.5N -> d = 7.29m).Obviously there's an error in my approach or math, just not sure where.
 >> Anonymous Wed Nov 11 14:31:40 2020 No.12331047 >>12314504I have a doubt with the simple linear regression model. Books say that, for[eqn]y_i=E(Y|X_i)+u_i[/eqn]$E(Y|X_i)$ is the systematic component and $u_i$ the random or stochastic component. My question is the following: even if we take the X values as "given" and not as random variables (which is one of the assumptions of the model) why is $E(Y|X_i)$ systematic when the coefficients are random variables, because they're based on sample information? What am I not getting here?I have a big confusion regarding what's a random variable and what's not in the model.
 >> Anonymous Wed Nov 11 14:41:02 2020 No.12331081 >>12331047From a purely autistic viewpoint, we model the $X_i$ as a random variable, since we're interested in the $theoretical$ linear impact a $theoretical$ variation in $X_i$ would cause on $Y$.But in $practice$ it's given data.
 >> Anonymous Wed Nov 11 14:44:34 2020 No.12331096 >>12330819>readingnonlinear dynamics>linklearn to internet>is vaporwar retardation a memeIdk desu
 >> Anonymous Wed Nov 11 14:53:12 2020 No.12331120 Can all 2nd order differential equations be evaluated to some combination of $Ae^{aix}+Be^{-bix}+Ce^{cx}+De^{-dx}$? Does this only apply when py"+qy'+ry=0, or can the RHS be $\neq0$?
 >> Anonymous Wed Nov 11 14:54:22 2020 No.12331124   >>12331047Linear model:$y_j=x_j+u_j$Expectation:$E[y_j]=E[x_j]+E[u_j]=E[x_j]$Conditional expectation:$E[y_j|x_j]=x_j+E[u_j]=x_j$So$y_j=E[y_j|x_j]+u_j$
 >> Anonymous Wed Nov 11 14:55:41 2020 No.12331128 >>12331124I hate the latex editor.
 >> Anonymous Wed Nov 11 14:57:18 2020 No.12331129 File: 27 KB, 344x461, 1466033420149.jpg [View same] [iqdb] [saucenao] [google] [report] >>12330799The way I do it is that I spam questions even if I feel "out of shape" or "not prepared" to tackle them because I never will be if I keep on using the mindset of "let me study a bit more so that I can be prepared when I do them." The good thing about math is that you never run out of questions so you will always have practice available.
 >> Anonymous Wed Nov 11 14:58:47 2020 No.12331136 >>12331047[eqn]y_j=\beta x_j + u_j[/eqn][eqn]E[y_j|x_j]=\beta x_j + E[u_j|x_j]=\beta x_j[/eqn][eqn]y_j=E[y_j|x_j]+u_j[/eqn]
 >> Anonymous Wed Nov 11 15:01:23 2020 No.12331144 File: 283 KB, 1200x1200, 1455332369244.jpg [View same] [iqdb] [saucenao] [google] [report] >>12327680I think the cute part is the expression and the eyes but the garbage part is also the eyes because it feels off if you look at it closely and the big tiddies which is rather out of character for her so you immediately feel some form of immersion-breaking (this is probably a super autistic/cringe way of saying it). Also, you're just trying to get us hard aren't you...
 >> Anonymous Wed Nov 11 15:08:37 2020 No.12331173 >>12331016>mgcos(theta)dThat's not a force
 >> Anonymous Wed Nov 11 15:10:50 2020 No.12331181 >>12331173it's still wrong if i do mgd, but thanks..
 >> Anonymous Wed Nov 11 15:11:11 2020 No.12331182   I have a matrix like this:[[a, b, c], [d, e, f], [g, h, i], [j, k, l]]I want to obtain a matrix like this:[adgj, adgk, adgl, adhj, ..., cfik, cfil]How do I do this?
 >> Anonymous Wed Nov 11 15:15:03 2020 No.12331198 >>12331181That's still not a force. m*g is a force
 >> Anonymous Wed Nov 11 15:16:20 2020 No.12331202 >>12331198he's doing work-energy theorem bro
 >> Anonymous Wed Nov 11 15:17:14 2020 No.12331209 I have a matrix like this: $\begin{matrix} a & b & c \\ d & e & f \\ g & h & i \\ j & k & l \end{matrix}$ I want to obtain a matrix like this: $\begin{matrix}adgj & adgk & adgl & adhj & \cdots & cfik & cfil \end{matrix}$ How do I do this?
 >> Anonymous Wed Nov 11 15:22:30 2020 No.12331235 How come we only have to worry about atmosphere overheating when a space capsule reenters the atmosphere? How come we don't have to worry about it when rockets leave the atmosphere?
 >> Anonymous Wed Nov 11 15:26:27 2020 No.12331259 >>12331202No he isn't>>12331209Jesus whyAnd in what form do you want it. As matrix multiplication?
 >> Anonymous Wed Nov 11 15:28:19 2020 No.12331267 >>12331259a, b, c etc are scalars.
 >> Anonymous Wed Nov 11 15:28:25 2020 No.12331269 >>12331209>How do I do this?you just did it
 >> Anonymous Wed Nov 11 15:30:30 2020 No.12331282 >>12331269Is there a faster way that might be implemented in common matrix libraries? Is there a name for this operation?I have two such matrices, and I'd like to compute ln(adgj) * a'd'g'j'. I know this is equivalent to (ln(a)+ln(d)+ln(g)+ln(j)) * a'd'g'j', but where do I go from there?
 >> Anonymous Wed Nov 11 15:30:39 2020 No.12331285 >>12331259>setting work done by friction equal to kinetic energy???
 >> Anonymous Wed Nov 11 15:33:10 2020 No.12331297 >>12331285>work done by friction ?>kinetic energy???
 >> Anonymous Wed Nov 11 15:39:03 2020 No.12331327 >>12331297sorry I barely read the question. work done by gravity and stored energy of the spring. no forces
 >> Anonymous Wed Nov 11 16:13:06 2020 No.12331462 >>12331235>How come we don't have to worry about it when rockets leave the atmosphere?we do
 >> Anonymous Wed Nov 11 16:25:01 2020 No.12331511 File: 227 KB, 600x600, 1548291770691.gif [View same] [iqdb] [saucenao] [google] [report] How does one go about asking the professor(s) for a research position? "Hey, could I work at your lab?" Or is there a better way of asking?
 >> Anonymous Wed Nov 11 16:25:03 2020 No.12331512 >>12331235that's one of the reasons why we don't blast rockets as fast as possible, because the drag and heating is worse for faster objectsthe reason we don't worry about it when they're leaving is because we make sure the capsules can withstand reentry, which is generally much much faster than escape, so if it can tolerate reentry it can tolerate escape
 >> Anonymous Wed Nov 11 16:43:21 2020 No.12331577 Z is a logical consequence of X, Y if Z is true in the truth table column(s) where both X, Y are true? What if Z has more true rows? Is it still a logical consequence?
 >> Anonymous Wed Nov 11 16:46:57 2020 No.12331590 >>12331120> Can all 2nd order differential equations be evaluated to some combination of $Ae^{aix}+Be^{-bix}+Ce^{cx}+De^{-dx}$?No.In the case where the characteristic polynomial doesn't have a duplicate root, the general form isAe^ax+Be^bx where a,b are complex.If you have a duplicate root, there's also a xe^kx term.> can the RHS be $\neq0$?If the RHS is non-zero, then the particular solution will typically involve the RHS plus its first and second integrals, and maybe some x^n*e^kx terms. The general solution is the particular solution plus the homogeneous solution.
 >> Anonymous Wed Nov 11 16:59:00 2020 No.12331653 >>12331144>big tiddies which is rather out of character for her>big titties are out of character for RemiliaKek.I do understand what you mean.>Also, you're just trying to get us hard aren't you...No.
 >> Anonymous Wed Nov 11 17:01:43 2020 No.12331660 >>12331577A -> B = (¬A) ∨ BIOW, the truth table for -> is[eqn]\begin{array}{c|c|c|c} A & B & A \rightarrow B \\ \hline 0 & 0 & 1 \\ 0 & 1 & 1 \\ 1 & 0 & 0 \\ 1 & 1 & 1 \end{array}[/eqn]
 >> Anonymous Wed Nov 11 17:03:48 2020 No.12331665 >>12331511seconding this
 >> Anonymous Wed Nov 11 17:21:08 2020 No.12331729 >>12331660logical consequence not implication
 >> Anonymous Wed Nov 11 17:24:55 2020 No.12331748 >>12330443>>12330626Agree with this anon. Princeton has an excellent undergrad program and world-class (literally ranked 1-3) mathematics graduate program. But Caltech is probably stronger for physics and engineering.
 >> Anonymous Wed Nov 11 18:28:23 2020 No.12332005 File: 87 KB, 1000x800, Real_Rotation.png [View same] [iqdb] [saucenao] [google] [report] How do you rotate functions in the real numbers?Like say I wanted to rotate f(x)=1/x by 45degCW. In the complex plane I'd just multiply by $e^{-i\frac{\pi}{2}}$, but how is it done in the reals?
 >> Anonymous Wed Nov 11 18:31:40 2020 No.12332018 File: 68 KB, 568x441, homework.jpg [View same] [iqdb] [saucenao] [google] [report] 3 physics questions i can't do itcan you guys help pls
 >> Anonymous Wed Nov 11 18:32:07 2020 No.12332024 >>12331511>come 15min late to exam>ace it>walk straight into the office afterward and say "hey, I'd like to do research in ___, is this the right group to join?"The answer will be "yes." If it's not, they're not worth your time.
 >> Anonymous Wed Nov 11 18:37:20 2020 No.12332052 >>12314504Updated, with input and thanks to >>12318590 >>12318721 >>12318758 >>12318916
 >> Anonymous Wed Nov 11 21:05:02 2020 No.12332465 Having trouble understanding a very simple physics conceptIn a Newton's cradle both energy and momentum need to be conserved, can someone explain to a brainlet why 2 balls moving half the velocity of the initial incoming ball would have the same momentum but more energy than the initial ball, and is therefore impossible?
 >> Anonymous Wed Nov 11 22:20:05 2020 No.12332583 >>12332465Less energy actually. Energy is proportional to v^2, momentum to v. So each of the half-speed balls has half the momentum and a quarter of the energy.
 >> Anonymous Wed Nov 11 22:33:42 2020 No.12332615 >>12332005Convert it to an implicit equation in x,y and rotate. So y=1/x=> xy=1A 45° rotation maps [x,y] to [(x-y)/√2, (x+y)/√2], so:=> ((x-y)/√2)((x+y)/√2)=1=> (x-y)(x+y)=2=> x^2-y^2=2c.f. x^2-y^2=1 which is the equation for the hyperbola with asymptotes y=x and y=-x, passing through (1,0) and (-1,0). x^2-y^2=2 is the same but with a scale factor of √2, passing through (√2,0) and (-√2,0). y=1/x passes through (1,1) which becomes (√2,0) upon rotation.BTW, note that you need to apply the inverse transformation to x,y. g(A.v)=f(v) => g(v)=f(A^-1.v).
 >> Anonymous Wed Nov 11 22:39:31 2020 No.12332624 File: 5 KB, 268x153, asdc.png [View same] [iqdb] [saucenao] [google] [report] >>12314504Ok, so I tried to make this question earlier but it was very badly formulated. So here it goes again. It's about linear regression.So, if I'm understanding it all right, when we want to do statistical inference with a linear regression model, we have to consider our observations (x, y) as random variables —because they have been extracted from random samples. BUT the Gauss-Markov assumption tells us that we have to consider the values of x as "fixed" in the sense that they're deterministic, not stochastic. First question: does this mean that only the y values are considered random variables? And, if the y's are random variables, then the coefficients (the betas) also are, and so are the residuals. If that reasoning is right, my question is the following, why does my textbook (which hasn't been helpful at all) say that the expected mean of Y given the values of x is the "systematic part"? That part depends on the values of x, which yes we said was systematic, but also of the coefficients. The coefficients depend, in turn, of the values of x and y. If Y is a random variable and each observation y is random with a certain probability, then the coefficients beta are also random variables. Why is it then that we call this part "systematic"? I have the feeling that I'm getting something incredibly wrong but I can't know what, my professor has completely dissappeared and the textbooks are not helpful.
 >> Anonymous Wed Nov 11 22:40:36 2020 No.12332626 >>12332624*By systematic I mean deterministic, the textbook uses both of these terms as exchangeable
 >> Anonymous Wed Nov 11 22:50:42 2020 No.12332644 >>12332615Well, you don't *have* to convert it to implicit form; you could just transform x,y in y=1/x to get(x+y)/√2 = 1/((x-y)/√2)then solve for y. But an implicit form usually works out neater.
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