/sci/ - Science & Math

how did bufaloo evoluve!

>>10619115
Moonstone. Next question.

Is there even any point of getting your IQ tested as an adult? Real tests cost money, and your education/career path is already mostly set, so wouldn't the only reason to do it be bragging rights? It can be estimated anyway with SAT and GRE scores, why would anyone need a more exact number?

>>10619146
>IQ
not science or math

>>10619146
>so wouldn't the only reason to do it be bragging rights?
yes, which is why only insecure copefags care about it

What is an equivalent of 1000 atm pressure? Something along the lines of "comparable to having 50 cars on your back" but true.

If X is a hausdorff topological space and A is a dense subset of X how would I go about showing that local compactness of A would imply that A is open?

>>10619306
comparable to having about 1000 cars on your back
assumptions: back width = 35cm, back height = 50cm, car weight = 4000 lbs

Creative ways to kill myself if I fail my calc III final? I have an A in the class and I got an 100 in both Calc I and II but the last unit was a bunch of gay bullshit and I don't really get it and I've been studying all weekend to no avail.

>>10619521
What part of it aren't you getting? Kelvin-Stokes?

>>10619525
My professor dropped Green's, Stoke's, and divergence theorem on us all in the last three days of class and expected us to have it all memorized for the final. I can do basic questions for all of them but my practice homework has a lot of really bullshit questions that are trying my brain.

>>10619521
calc 3 was pretty gay in general
you learn the equations for a doughnut.

>>10619535
Shh, shhh, I'll tell you a secret.
[math] \int_{\partial W} f = \int_{W} df[/math]

>>10619543
I'm not really sure how this is supposed to help me

okay I'm the same fag with a calc III final tomorrow. I get to write shit on an index card and bring it in the test with me what the hell should I write?
I've already put stuff that I have a feeling I'll forget like the fundamental theorem of line integrals.

>>10619338
That's perfect, thank you very much.

>>10619569
>puts the single most trivial result on the card
God fucking dammit lad.
Put the big autistic formulas, you can remember the easy stuff on your own.

>>10619549
Green's, Stokes' and the Divergence theorem are merely special cases of the generalized Stokes theorem, which >>10619543 simply stated.

>>10619579
It takes up barely any space and I always forget it like a retard. I already have green's, stoke's, and divergence theorem memorized so I don't need to waste space on those.
Often times the tests are just the homework with the numbers changed around so I'm tempted to just write out the full solutions to some of those on the index card. I don't think there are any big autistic formulas in calc III.

>>10619588
Kelvin Stokes is big and autistic.

>>10619584
If he were smart enough to understand that, he wouldn't be failing undergrad math

>>10619625
>reading comprehension

Is it better to go for a bachelors in EE and masters in CE, or CE all the way?
Should I even go into CE if I don't want to be a cuck codemonkey?

Redpill me on bilinear interpolation.
I get confused by 5+ variables with similar name.

What does this symbol mean help i have a final tomorrow

I mentally checked out of math class very early in life.
Now that I see the applications, I want to learn discrete mathematics and algorithms, but there's a huge gap of knowledge between me and the basic texts on these subjects.
How do I efficiently close that gap? Is there a "Strunk and White" of highschool math, or is there a classic textbook you can recommend?

>>10619786
the intersection over all A_k
the fuck else would it mean

>>10619786
the infinite intersection of all the [math]A_k[/math] sets, with [math]k \in \mathbb N[/math]. That is, [math]A_1 \cap A_2 \cap A_3 \cap \hdots[/math]

>>10619521
i'm literally in the same shituation, with calc 3 too. maybe we can dual suicide anon

Brainlet here, how much math do I need to know(i.e. graduate level etc)before properly understanding numberphile videos? The same goes for computerphile.

looking for the area of the shaded portions, did I do it right?

>>10619911
for more clarification, areas for polar graphs

When you zero out a measurement, for example if you measure the weight of an empty beaker and then measure it again with varying amounts of liquid inside, once you subtract the weight of the empty beaker, what do you call those measurements when giving them their own column on a data sheet? I feel like I have it on the tip of my fucking tongue!

over a decade ago i came across something online about a theorem or something where some mathematician basically claimed:

>you can only derive from from something, whats inherently in it

which I though was the dumbest thing in the world. was basically saying that if you have a box with 3 things in it, you could only ever take 3 things out. i thought it was like saying that the sky was blue and claiming you were the first to notice it even though its ubiquitous.

but then a few years later I randomly had this epiphany that the theorem could allow you to place boundaries on something even if you dont know what the boundaries are yet.

Ive tried multiple times to try and find it again but cant. does anyone know who/what it is?

>>10620029
net weight?

net weight = gross - tare = laden - unladed

>>10619752
computer engineering isnt a real thing. on behalf of all engineers everywhere, stop calling it engineering

>>10619569
just write pi because all things in the universe can be found within it. apparently.

>>10620057
>net weigh
Oh fuck me in the ass how can I be this dumb? Thanks so much you absolute brainlord!

Any tips to shake myself out of a depressed/lazy spiral and actually catch up on my college work? I just feel incredibly drained all the time and the prospect of sitting down for 3 fucking hours to listen to a lecture and take notes fills me with utter dread. I only have 1 or 2 classes a day but after those I just feel mentally wiped and spend the rest of my time doing normie shit or at my part time job.

I'm behind on approximately 10 hours of lecture content and now have assignments to do as well which will take priority. I'm not a complete turboautist and only see college as a means to get a job, and treat most of the content with the triviality and resentment is deserves.

I'm designing a heatsink, well I have a design that I'm calculating for. With fin efficiency at 0.91
Q=hA(Tb-T)x(number of fins)
Tb is the temperature I desire at the boundsry. This comes out to like 4 watts when it is at perfect temperature. What do I do now?

The initial boundary temp is 85. The desired is 63. How do I know if my heatsink will cool it from 85? Do I calculate the material now?

For aluminum with my heatsink mass to go from 85 degrees to 63 only requires like 1.4 watts or so.

Does this mean my 4 watts will be overkill and cool well below 63?

Do I need to make Q=1.4 watts by reducing surface area now?

Someone please help me, this is confusing

>>10620124
lift weights 5 days a week for an hour each day

drink a pint of whole milk before bed (lactose and galactose are the best fuel source for the brain)

pick a carb and cut it out completely. like either bread or pasta.

cut out sugary drinks all together and replace with water. sugar free energy drinks ok.

set a bed time and stick to it. no computer, cell phone, tv, etc. set your alarm with your phone and plug it in on the other side of the room so you have to get up to get it.

also, make the room cold if you can. studies have shown that cold rooms help you sleep better.

5 hr energy is good for test days.

let yourself have short naps of like 1 half hour nap a day.

get vitamin D. sunlight is best, 85% of vit D generated in the skin by the sun is absorbed, while only 30% of ingested is. Vit D supps are cheap and especially good for winter months.

get a SAD lamp from amazon and shine it on you while you eat. it will help you wake up
>pic related

make friends you can study with. ask some people if they want to meet up in the school library and quickly go over what happened the past week.
>In law school this was prob the most helpful thing I did in terms of keeping up in class. plus it was fun to joke around about our common misery and professors at the same time.

set incentives for yourself. I used getting myself a starbucks as a motivation to get out of bed.

also generally taking care of your personal hygene has a lowkey/subliminal effect on feeling more aware ive noticed. in undergrad I didnt exercise, ate like garbage, didnt shave often enough, didnt care what I was wearing so much, just buzzed my hair when i felt it was too long, ets.. Now that I take more pride in my personal appearance Ive noticed that I feel more engaged in whats going on around me.


>but really the biggest ones youll notice right off are lifting, sleeping, and cutting a good amount of sugar from your diet. the rest will help too but it will take longer.

>>10620142
I havent taken or used heat transfer for a long time, but generally speaking you'll want to minimize material while holding your boundary constant at the desired temp. so set Tb at what you want, and work backwards.
so,
>Do I need to make Q=1.4 watts by reducing surface area now?
yes, this is correct.

you want that because its good practice for if you ever send something for mass production, a little bit of mass * 750,000 units is a lot of mass you have to pay $$$$ for. though I would over define the cooling you want by a small amount to be on the safe side. Q=1.45 watts or something as a safety net.

>>10620165
Problem is I already do most of that shit. Probably the only one I don't adhere to is the sunlight and friends part, and that isn't going to change anytime soon thanks to my work and class schedule meaning I never actually go and just listen to the lectures later.

>>10620170
Fuark. I already sent my aluminum block for cutting. The mass is too much, and it's already overkill by the sound of it. I'm gonna see how effective it is tomorrow, I'm sure that safety net you mention is important because the connection between my heat sink and the heater may not be perfect.

It'll be difficult to lower mass without being able to make thinner fins. I'll probably just end up cutting off a few fins and shortening the whole thing. I missed the point of the assignment, didn't take mass into account with the initial design

Thanks anon

>>10620180
ask for different work hours, or look for another job?

>>10620186
>the connection between my heat sink and the heater may not be perfect
thermal flux or solder it

>It'll be difficult to lower mass without being able to make thinner fins. I'll probably just end up cutting off a few fins
research how others have designed cooling fin arrangements or try to think of alternate layouts. I dont know for sure, but nature usually gets it right. see if there is a fractal design you can use to layout the cooling fins.

does anyone have a glossary of direct methods to deal with simple pdes and odes without complex analysis?

>>10619321
A being closed would violate the Hausdorff condition.

When something is dissolved, does it always maintain exactly the same density it had before? I ask because I'm not sure if things like extreme temperatures or weird molecular configurations can do strange things that aren't immediately obvious.

Pic related is the top of a viewing frustum at a 45 deg angle.
Why does x = z (or -z)? What does that mean?

>>10620499
|x| is defined as x when x>=0 and -x otherwise.
Set z=|x|.

>>10620223
>implying

In the perspective projection matrix in pic related, what to alpha and beta represent, and why is [3,2] = -1?

I failed calc II because of extreme testing anxiety and poor algebra skills
now what

Anyone here heard about "analisis antiquorum"?
It's a very basic method of solving equations, where you assume something is a solution of an equation and then upon that assumption you do stuff on the equation in order to find it's roots. It often goes hand in hand with method of equivalent equations.
My problem is, it apparently isn't called like that in english (google doesn't return anything) and I can't find how it's called in english. Anyone?

>>10620602
Can you give an example?

>>10620602
http://www.math.edu.pl/metoda-analizy-starozytnych was literally the only link I could find about the subject.
It doesn't really have a name elsewhere.

>>10620623
yeah, that's my problem - it's everywhere in polish books, old and new, but I can't find the name of the english counterpart
>>10620613
Say, we have an equation:
[eqn] \frac{2x+1}{x}=\frac{1}{x}+x [/eqn]
Lets assume it has at least one root, and one of those roots is a. If we put a into the equation we get an equation which is true, and since it is true we can do stuff on it:
[eqn] \frac{2a+1}{a}=\frac{1}{a}+a [/eqn]
[eqn] 2a+1=1+a^2 [/eqn]
[eqn] 2a-a^2=0 [/eqn]
[eqn] a\left ( 2-a \right )=0 [/eqn]
hence it implies an equation [math] a\left ( 2-a \right )=0 [/math] which is also true. It has two roots a=0 and a=2, so if the equations has any solutions it has to be one of them, which we check by substituting them back to the original equation.
I'm not so sure about this myself, It's kinda vague for me and that's why I wanted to learn more about it if it really is what I think it is. Plato supposedly invented it, so I think it might've made more sense before algebra. It's also called "inference from assumption" in polish (it's a direct translation, so I doubt it's called like that in irl). It's often put together with the method of equivalent equations as a contras to it.

>>10620425
solids and liquids can change density, but its usually negligible under regular conditions on earth. water becomes more dense as it cools until it gets to 2C, then it begins expanding until it freezes. thats why ice floats

gases can change density a lot based on temperature.

and when anything becomes a plasma its density will change in meaningful ways.

if youre dissolving chemicals into other chemicals it can change density based on how the electron clouds bond with each other, but again, its pretty small in the grand scheme of things.

What does "affine" mean?
I see stuff like affine transformations and affine coordinates but I don't know what it means.

>>10620706
Affine is anything of the form a(x)=l(x)+b, where l is linear.

what are homogeneous coordinates used for in computer graphics?
are they used for both oblique and perspective transformations/projections?

>>10620771
One benefit is that you can put translations into the transformation matrices.

I've recently started studying QFT and i've seen the path integral written as:

[eqn] \mathcal{Z} = \left< 0 \big| \, e^{-i\hat{ \mathcal{H} } t} \, \big| 0 \right> [/eqn]

where [math] |0> [/math] is the ground state. Why does this make sense? Why take the transition amplitude from the GS to the GS? Any help appreciated. (pic unrelated)

Is this just impostor syndrome or am I a legitimate fraud?
>ace almost all of my exams and assignments every time
>high GPA
>professors love me
>in reality I have no idea what the fuck is happening for most of the semester
>go into full damage control in the last 2-3 weeks and spend 8 hours a day cramming and making/doing Anki cards
>do assignments 2 days before they're due in bursts of nervous activity where I can write thousands of words in a few hours and have 40 tabs of references open at once
Will this all fall through at some point or am I good? I remember jack shit once my exams are over.

>>10620223
A is a subspace...wut?

>>10620846
>I remember jack shit once my exams are over.
that part might be a problem as you get to the higher levels and things build on earlier classes more. I'd guess...I don't really know

I want to take 5 classes and do really well on them, read for 30 minutes a day, study Russian for 1 hour and 30 minutes a day and work out regularly, all without sacrificing sleep and with enough time left to program stuff that interests me, prepare for programming competitions and have some time to relax.
Is that even possible? How would I do that? Any tips?

>>10621032
adapt the habits very slowly. baby steps. otherwise you will last a few weeks max, probably less if you're used to browsing 4chan, playing vidya etc.

>>10620833
You start at ground state and go to ground state and are looking and all the shit that can happen in between (all the loop calculations) from GS to GS is the vacuum expectation value. In general you'll go from one state phi to another state psi which will be a transition amplitude.

>>10620706
do you know what "linear" means ?

>>10621032
You have limited time, something must be sacrificed. If you're not going to give up sleep (which I don't think you should) you'll need to sacrifice 4chan, social life, hobbies, etc. Also, find efficient sleep patterns and study habits. While in classes, actually pay attention and apply it so you're using your class time wisely

>>10621037
Okay. Then the choice of initial and final state is arbitrary because whatever i choose is the same: "anything can happen between the two states"?
And choosing the GS just makes it easier since we'll probably have it?

I asked my professor today what the transition amplitude from the vacuum to itself means and he told me that it doesn't have a meaning and that its trivial. That perplexed things a bit.

>>10621156
There are restrictions that come from the difference between states, but if you are going from one state back to itself, what matters are the interactions you may have connected to the initial and final states. For example, if it's vacuum, you must have a pair creation, but if you are starting with two protons, you can start with two gluons of different (non-annihilating) color charge. The process is the same so yeah "it doesn't matter" but the endpoints will change around what things can be included and what cannot.

What is the equation for this curve and how can you derive it mathematically?
https://youtu.be/gM3zP72-rJE?t=46

>>10619111
does this circuit work?

Any hints on how to construct such a function, that it produces an image of a whole real line for any given interval?
My idea is a function, which is equal to 0 for any rational number, and whose left and right limits are +inf and -inf for any rational numbers. But I don't know if such a thing is a function at all.

Can someone tell me why medicine is so retarted comparing to other disciplines.

People has been doing that since they have started to exist.
For me it is amazing how engineering, science, math has developed, and is developing.
Although fucking human body is still one big unknown.
I probably(diagnosis takes even up to 10 years xD!) ankylosing spondylitis.
Medicine know shit about that, about arthisis in general.
Not even talking about cancer, but these diseases are very old.
Despite that medicine is still at the level of just pain relief, nothing besides that.
It is chronic disease and people are just left to live like that, pain sometimes makes me want to kill myself.

Obviously I respect meds and dont want to sound dumb, but it is really fascinating to me.
Are there any developments in arthisis or cancer?

How do I force myself to read babby texts after getting used to grad texts?

>>10621724
Skim them. The information density is so reduced that you should be able to parse a whole page just by looking at what's boxed/underlined.

>>10621773
>boxed/underlined
That's exactly the problem, jack is highlighted.
I can start skimming somewhat well, but I usually end up speeding up more than I should.

Yea, I'm not sure why its 12 ohms instead of 29 ohms. Help pls.

>>10621328
Spice thinks it does.

>>10620576
α and β determine the scale and offset of the transformed Z coordinate. The matrix transforms [x,y,z,1] to [x,y,αz+β,-z], which is equivalent to the Euclidean vector [-x/z,-y/z,-α-β/z)]

They are typically derived from the near and far distances. α=(n+f)/(n-f), β=2nf/(n-f). With these values, z=-n->z'=-1 and z=-f->z'=1. The -1 in the bottom row swaps the coordinate system from left-handed (view direction is the negative Z axis) to right handed (view direction is the positive Z axis).

>>10620771
Using homogeneous coordinates means that both translation and perspective projection can be expressed as linear transformations. A linear transformation always maps zero to zero, so any linear transformation will leave (0,0,0) untouched, but can put (0,0,0,1) wherever you like.

Also, it implicitly converts polynomial functions (e.g. Bézier curves and surfaces) to rational functions, so you can represent circles and ellipses exactly.

What are the units of tension in a string?

Can someone help my dumb ass out with differential equations?

I'm having trouble understanding the basic reasoning behind what a general solution is and why it matters. The basic way I understand it now is this:

We are presented with a linear diff eq. In solving it, we find a function that satisfies the diff eq for all values of the independent variable.

Ao then let's say that we are just doing some fucking textbook problems and we are presented with some random linear diff eq that is equal to some nonzero constant. We find a function that satisfies the eqn, but then in order to find a "general solution" we have to change that nonzero constant to zero, then find a solution that may or may not be different from the one we found when the constant that the diff eq was equal to was not equal to zero.

Then we add the solution that satisfies the nonzero constant equation, and the one that satisfies the zero equation, and for some fucking reason that is the general solution? And then we just add initial conditions because fuck it?

I'm so fucking confused, why do we add the particular solution and complementary function? Why?? And when the fuck to I add initial conditions? What's even the physical interpretation of a diff eq? How are they fucming useful? I don't understand, I've been ripping my hair out over trying to just wrap my head around the most basic fucking explanations of this shit, I'm so god damn frustrated, please someone explain this to me so a brainlet can understand.

>>10622217
Previously those were just naval tons, because the concept was so important in the sailing era.

I think currently, we use New tons.

>>10622254
Whoa, I don't think i have the time to write a wall of text that would be required to pull you up from your plane of confusion, but I'll try my best.

Let's use a physical system so we can picture everything in our minds. Take a spring or slinky, suspend it tied to the ceiling, carefully let go. What happens? Nothing moves. The slinky is pulled down by gravity, and it creates an opposing force through Hooke's law.

That's the limit of the general solution. The initial condition would be the point and velocity of the free end of the slinky at t=0. If you pull it down and let go, it will oscillate for a bit, until the friction eventually dampens the motion, and you'll end up with the same image as before.

So, the initial condition is a single set of properties, at one point in time or space.

A particular solution is the result of something different, because it is not only a single point in time or space. Again, using the slinky example: If you suspend the thing and then do nothing, that corresponds to a force diagram with a "= 0" on the other side, and, as previously mentioned, gravity and Hooke's spring force cancelling each other out on the other side of the equation.

Now imagine you don't let go, but maybe wiggle the free end around in a sinusoidal motion, maybe. Or you constantly hold it at a fixed point, without letting go (constant, non-zero input).

I hope you can put it together now:
- homogeneous solution: what the system naturally does
- particular solution: what the system does with an input you provide (Just accept that you can add those to get the complete solution, for now. Or, you can take a look at the proof yourself..)
- initial condition: from which point in phase-space does the solution you're interested in start?

There, coffee cup's empty, I sincerely hope that helped. Good Luck.

If I have a collection of points of interest in a finite 3D space of which I know the distance to each point from anywhere, will 4 non-planar points be enough to recreate the finite space and points? Also, is 4 enough if you measure all of them from a different point of interest, or do you need spots in arbitrary space that are not POI? If I'm programming something to tabulate these points, how will I know I have enough "resolution" in my memory storage to account for cases like near-planar points or closely-clustered points?

>>10622254
because ode's are so hard to solve the general method is literally guess a solution then run it through the ode (homogenous equation assumes a solution of y=e^rx then the roots of that equation determine r and the form of the guessed solution)
you can add the particular and homogeneous equation because your homogeneous accounts for one part of it and the particular accounts for the nonzero part. it's a special property of the linearity of the solution, effectively equal to splitting 2 into 1 + 1.

>>10621459
because biology at the scale of humans is incredibly complex and can't be abstracted like the other things you mentioned. there is a lot that your body does and even more that can go wrong. compounding this with how unhealthy people are and how the survival of the fittest is no longer true at all you get a ton of problems that can arise during your life

>>10621326
i'm not sure what the equation is and i don't think you can derive it easily mathematically
https://arxiv.org/ftp/arxiv/papers/1501/1501.06981.pdf
>If the contacting area of the skate to ice is 150x10^-6 m^2 (1 mm wide and 150 mm long) and the skater weighs 500 Newtons, the pressure applied will be 3.3 MPa. As the melting point of ice falls by 0.0072 °C for each additional atm (0.1 MPa) of pressure applied, the melting point will drop by 0.24 °C only.
above shows that it's more of an empirical quality just like how thermometers exploit the expansion of a liquid due to temperature
https://en.wikipedia.org/wiki/Thermal_expansion

Hi, I'm just starting out with math, working my way through Gelfand's Algebra.

I'm wondering why he's making such a big deal out of binomial expansion. Do you guys see [math] (a * b)^7 [/math] and just instantly know what all the expansion coefficients are? Did you memorize Pascal's triangle or what? I get that the powers form a "palindrome" also (if that's the right word) but I don't really see how one immediately derives the coefficients... Sorry about being a total baby here, I'm just looking to learn more.

>>10622882
you only need to memorize one side of pascal's triangle as it's symmetric. binomial expansions are exceedingly common especially in pure math

>>10622882
Actually nevermind, I get it. You sum the previous coefficients. That's pretty cool.

>>10622887
It seems to me like learning algebra actually takes a lot more work to internalize than I remember from way back in high school. How much time do you figure it would take a brainlet like me to get form a solid foundation before moving onto calculus (I can spend about 4-5 hours a day on math)? I'm not very smart but I'm extremely interested and motivated.

>>10622893
once you start using it more and more it becomes like a language and you can start thinking about it like you're fluent. the majority of calculus is just learning two new operations (derivatives and integrals) like addition and subtraction and the meaning behind them. they are simple (when actually practiced above calc 2 that is) and just need practice to get. if you're motivated enough that's all you need as diligence gets you far and intelligence only helps

>>10622900
I understand integrals and derivatives on a very basic level. And I can write a simple python algorithm to compute both by hamfistedly summing a bunch of rectangles or calculating the slope of a tiny euclidean distance at a chosen "point" on a curve. I suppose I just lack direction, as I'm totally self taught. I'd really like to go into electrical engineering but all of my friends are absolute (with emphasis) fools and I don't really have anyone to ask questions except , as of recently, you people here.

>>10620722
>>10621045
I don't know. To do with lines or points along a line?

Color blindness is when you can't see color or see it well

_____?_____ is when you can't do work or do it well

>>10622918
could always take a local class at your college/try auditing something. interaction is very helpful when it comes to learning things like this as you've noticed. if you think about them graphically that's mostly what you need as the summing a bunch of rectangles and limit definition of a derivative are actually newer than both derivatives and integrals. just study what you want and the prerequisites for it. asking professors or similar positions at a college/university would also help guide you

>>10622925
incompetency is the literal word for that but you're describing a blanket term for it when it's case by case

What do you call a mathematical model that describes a system while not taking its physical principles into account? I.e. the curves fit the empirical data points but are not derived from physical principles, they're just a convenient hack. It's been on the tip of my tongue for half an hour.

>>10622925
_Avolition_, as a symptom of various forms of psychopathology, is the decrease in the motivation to initiate and perform self-directed purposeful activities. Such activities that appear to be neglected usually include routine activities, including hobbies, going to work and/or school, and most notably, engaging in social activities.

_Hedonism_ is a school of thought that argues that the pursuit of pleasure and intrinsic goods are the primary or most important goals of human life. A hedonist strives to maximize net pleasure (pleasure minus pain).

What markers increase your intellectual interest in a person?

>>10620706
An affine space is a vector space in which the origin has been removed. In that sense, you cannot just add vectors but only subtract them. Imagine for example a plane in [math] \mathbb{R} ^3 [/math] which does not contain the origin. If you try taking two points in the plane, draw the vectors from the origin to the points and then add them, the result will not be in the plane.

An affine transformation is a linear transformation that preserves angles, parallel lines, points etc, which can always take the form [eqn] f(v)= \mathbb{M} v + w [/eqn] where [math]\mathbb{M} [/math] is a matrix and w is a vector of the target vector space. If you have any experience with Galilean relativity, the Galilean transformations are affine transformations, composed by a rotation (represented as a 4x4 matrix) and a boost (represented as a 4-vector). In that sense, Galilean space time is affine.

>>10622945
math

In the basic perspective projection matrix in pic related, what do alpha and beta stand for? What do they do?

>>10622945
https://www.dartmouth.edu/~matc/MathDrama/reading/Wigner.html

>>10622964
Your first post
>>10620576
was answered
>>10622162

>>10622254
> why do we add the particular solution and complementary function?
If you have f(t)=y and g(t)=0, then f(t)+g(t)=y and also f(t)+a*g(t)=y for any scalar a. Furthermore, if you have multiple homogeneous solutions g(t)=0 and h(t)=0, then f(t)+a*g(t)+b*h(t)=y for any scalars a and b.

IOW, a differential equation typically has infinitely many solutions. In fact, it usually has an N-dimensional space of solutions where N is the number of independent solutions to the homogeneous equation. To get a specific solution, you need to know not only the equation but also its initial conditions.

Consider a mass attached to a spring. The homogeneous differential equation is m*x''(t)+k*x(t)=0 where m is the mass and k is the spring constant. Note that both x(t)=sin(w*t) and x(t)=cos(w*t) (where w^2=k/m) are solutions. So if x(t) is a solution to m*x''(t)+k*x(t)=f(t), so is x(t)+a*cos(w*t)+b*sin(w*t) for any a,b. Note that at t=0, a*cos(w*t)=a and d(b*sin(w*t))/dt=w*b. So given the initial displacement and velocity of the mass (i.e. x(0) and x'(0)) you can calculate a and b. Also: a*cos(x)+b*sin(x)=r*sin(x+phi) where tan(phi)=a/b and r=sqrt(a^2+b^2). IOW, the initial conditions give the phase and magnitude of the oscillation, while the frequency is determined by the mass and spring constant (i.e. the frequency is a property of the system itself).

>>10622217
Tension is a force so whatever unit of force you prefer, typically chosen to be Newtons

AD and BC are line segments of equal length normal to the x-axis, the curve connecting D and C is of fixed length, what shape does that curve of fixed length take such that the area described by lines DA, AB, BC and that curve is maximised, Think it's a circle but not sure

https://www.youtube.com/channel/UCSs4A6HYKmHA2MG_0z-F0xw

Anyone know more channels similar to this but in English or French ? Hence even russian if it have high quality subtitles that youtube can auto translate .

Why do you need to "linearly interpolate coordinates"?
How does that work? I thought a coordinate was a coordinate. What would you be interpolating with?

>>10619521
Helium

>>10623505
It depends upon the length of the curve relative to AD. When AD is zero, the optimal curve is a semicircle. As AD gets longer, increasing AB (and thus the area of the rectangle) has a greater effect than increasing the area above the rectangle, so the optimal curve will approach a horizontal line.

>>10622254
it seems like you really don't have any clue what a differential equation is
just watch the 3 blue 1 brown video on it that was released recently.
if you know any linear algebra, this would be much easier to understand. i don't really see how to explain the whole "particular solution" thing without that.

>>10619111
Are upper division Computer Science courses worth it?
I’d prefer to get the BS degree and a job then be done with college yet my mom insists otherwise.

>>10623552
A triangle has spatial coordinates and e.g. texture coordinates at each vertex. The spatial and texture coordinates of any point in the interior are obtained by linearly-interpolating between the coordinates at the vertices, with the same interpolation parameters used for both. This results in an affine mapping between texture coordinates and spatial coordinates.

>>10621459
>Despite that medicine is still at the level of just pain relief, nothing besides that.
Because you cant just redesign people.
A lot of those problems are just systemic. Every terrestrial vertebrate will develop back pain over their lives because we've all basically got fish-skeletons with goofy flippers. It works, but it's not optimal.

>>10619111
Uniroincally have a 2500 word essay due in 15 hours which can decide whether or not I graduate. Have done zero words. Feel zero pressure whatsoever.
I think I'm mentally ill for not feeling anything.

On a side note, do you think drug use can trigger mental illness or mental illness triggers drug use?

The solution to [eqn]x>x^2[/eqn]
is obviously [math]1>x>0[/math], but is there a way to solve this algebraically? For example, if I divide both sides by [math]x,x\neq0[/math] I get [math]1>x[/math] but this is obviously not the whole story. I've found a way to solve this by testing for 0s and then looking at the signs but that's not what I'm asking for, I want to know how to solve this using the rules of algebra.

>>10624049
there isnt another way
algebra uses equations, not inequalities
you transform inequalities into equations by splitting them up
x > x^2
0 > x^2 - x
0 > x(x-1)
then solve for the zeros and check signs
thats just the way you solve it

Can someone explain the full pipeline process of getting to different coordinate systems in computer graphics?
I don't know what the fuck a camera matrix is meant to be and what the product of multiplying it does, or how you get to NDC from it. I'm so fucking confused.

>>10624069
thanks for the explanation

>>10623536
Bump

>>10619146
There's an interesting paper about people having a very hard time making friends with people that have a difference of over 20 IQ points to them

It's true in my experience, I joined mensa, and made quite a lot of friends there

>>10619879
depends on the education level in your country, all of the where easily understandable for me in high school

>>10620846
sounds standard, don't worry
working on improving is definitely a good idea though

Can anybody tell me how to solve the problem A at the bottom?
I've been trying with no results

>>10623887
You want help with that essay?
Drugs can serve as a tipping impulse to an already unstable brain but doesn't happen often, and when it does, it's often fully reversible. But still.

>>10619111
Are quantum fluctuations more common in deep space? Where gravity from mass has less of an effect on the warping of space?

>>10624465
we all know [math]f(t)[/math] looks like this.

>>10624465
your vertical shift is going to be the starting temperature of the room, your delta T value is obvious and you can figure that out, the e^kt expression is just the natural exponent raised to the power of the product of the time in question and some constant k which you again can easily figure out. You could solve this in 2 minutes if you think about it carefully.

>>10624836
The problem is that i'm not sure how to find k...

>>10623600
If you want to learn actual computer science, yes

>>10619521
whats so hard about it? doing calc 1 right now. isnt easy peasy i'll learn 16 minutes on the way before test lemonsqueezy but what makes calc 3 hard especially?

>>10623600
>>10624988
and youll get paid more

I buy something for $14, I resell for $15 with a 3% tax, hence I get back $14.55 back which is a $0.45 profit.
I want to resell x amount until I make enough to buy another item for $14.
I’m thinking $0.45x = $14
So I need to sell 31 to make a $14 profit
Is this wrong?
I’m also thinking (14.55)*21 = $378.3 is how much you make from selling 21 at 15 after taxes.
Buy 26 for 14 = 14.3

So from the second method, I only need to sell 26 to buy an extra item, but the first method says i need to sell more.

Any ideas what I did wrong?

>I’m also thinking (14.55)*21 = $378.3 is how much you make from selling 21 at 15 after taxes.
Should be 26, not 21

>>10624465
I'm just as confused as you are anon.
We need to know what k is, or at least know 2 points on the temperature graph so we can find out what k is, but we only know 1 point.
So this doesn't seem solvable.

>>10625048
it's $0.55 profit, not $0.45

>>10625099
wow im so dumb

>>10625052
I was stressing out with this! Thanks for telling me

>>10624169
Object coordinates are transformed by the model matrix to get world coordinates, which are transformed by the view matrix to get eye coordinates, which are transformed by the projection matrix to get clip coordinates, which are divided through by w (projective division) to get normalised device coordinates (NDC), which are transformed by the viewport and depth transformations to get window coordinates.

The first two steps are often merged, with a single model-view matrix transforming from object coordinates directly to eye coordinates, skipping world coordinates. The third step can sometimes be merged, with a single model-view-projection matrix, but lighting typically needs a coordinate system which is affine to world space, so if you're using a perspective projection and you're doing lighting the projection matrix needs to be separate.


> I don't know what the fuck a camera matrix is meant to be
It's the position and orientation of the camera. The view matrix is the inverse of the camera matrix.

> and what the product of multiplying it does
Multiplying a matrix by a vector transforms the vector. Multiplying matrices composes the mappings. Matrix multiplication is associative, so (A*B)*v = A*(B*v), i.e. transforming a vector by A*B is equivalent to transforming it by B then A. In a transformation hierarchy, the left-most matrix in the multiplication is the parent and the right-most is the child. This assumes that the final multiplication has a column vector on the right; if you're using ass-backwards DirectX conventions, then you have v*B*A where v is a row vector and A and B are transposed: (A*B)^T=(B^T)*(A^T).

> or how you get to NDC from it. I'm so fucking confused.
The projection matrix transforms from eye coordinates to clip coordinates. NDC is clip coordinates after projective division (you have to do clipping first to avoid dividing by zero or projecting points behind the viewpoint).

i just calculated 56 MPa is the pressure required for air to have the same density as water.

if there was 1kg of air in a perfect weightless bladder at the depth where pressure is 56 MPa, would it keep sinking deeper? this is about what halfway down the mariana trench is at around 3 degrees celsius.

Am i missing something? why does air require so much pressure when it's made up mostly of nitrogen and oxygen which are much heavier than hydrogen which is what water mostly is? Would oxygen and nitrogen become liquid at these levels?

why are liquid molecules allowed to be so much nearer each other than gaseous?

>>10624684
>Have anxiety
>Take weed
>Get full blown panic attack about possibility of getting schizophrenia
>Next week is anxiety x10
I fucking hate being so worried all the time. I can't do anything fun.

For a holomorphic function [math]f=u+iv[/math], Cauchy Riemann implies [math]u_x=v_y,u_y=-v_x[/math].

But how can you write [math]f'[/math] from [math]u_x,u_y,v_x,v_y[/math]? I know there's a way but I can't find it anywhere right now.

>>10626111
I refuse to work with homophobic functions

>>10619111
How can i put multiple operations under the same root in a casio calculator?

>>10626315
use parantheses?

>>10626367
It worked, thanks anon

how am i supposed to read these two graphs? i understand the topic just don't know what the graphs are trying to show.

Indeed stupid question that makes me question my own intelligence or if Im just very tired.

Exercise gives speed at aphelium and peryhelium of certain planetoid and ask to "calculate speed at semi-minor axis".

I mean what they actually ask for? Since speed will be function of radius which is changing between Ra and Rp. At what point exactly? Im confused and kindly ask what could they actually expect.

>>10626912
uhm at the red points?

What does "linear" mean? Can you make it as braindead as possible?
I see things like "linear interpolation" but don't know what that means. What's so "linear" about it and what can you compare it to?

>>10627075

No idea why somebody would need speed at those points but thank you. I guess now I have to calculate relation between Ra, Rp and b parameter from eccentricity.

I guess the problem was purely related to my language where sentence used in exercise "velocity at semi-minor axis" in english, here could as well mean "velocity between perihelion and aphelion". Not really precise choice of words.

>>10627153
>Can you make it as braindead as possible?
sure

Linear refers to straight lines.
Linear interpolation connects points using straight lines.

If a steady, non-changing current is flowing through an inductor, does that mean the voltage through the inductor is zero?

>>10619111
How can I find the vector between a hyperplane represented by a linear system, and a point.

For example, the vector from point (1/2, 1/2, 1/2) to the line represented by x+y=1, y+z=1

I have found resources that explain how to do it with a hyperplane represented by a single equation, but not by a linear system that can't be represented by a single equation

Should I quit my job after this summer to focus on school?
18 Units next semester, all major classes (I'm an electrical engineering student). I don't think I've ever taken this many units, and if I did, it 100% would have been with general ed classes.

>>10627489
>18 units
How many hours a day is that?

i poop once a week is this normal

>>10627503
youtube.com/watch?v=xMXSNNAL6FA&t=128

>>10627495
16.6 hrs a week.
Each day all over the place.

>>10627609
>16 hours a week
I know niggas juggling 20 hours a week of classes with full time jobs, you'll be fine.

>>10627609

And I didn't complain about my 30 hours of classes, lectures and labs per week...

>>10627697
How many units is that and what country? That sounds really excessive.

>>10627697
There’s no way it’s possible to actually get anything out of these classes while working part/full time. You’d probably be bullshitting everything and memorizing instead of actually learning.

Can you help me out /sci/? I'm doing an assessment for a job I really want but I'm stuck on this question.

>>10627793
4

>>10627793
>>10627793
4.
>my teachers gave an IQ test question as an assignment

>>10627793
>>10627797
this

>>10627793
I’m pretty sure I know the answer, but I don’t want to tell you because someone else who can solve it than asking someone else is better suited for the position, like me.

>>10627797
>>10627799
thanks lads, it was correct

>>10627803
The position is located in Romania, I doubt you would want to work there

>>10627813
I would. Is the job market good for economists and related areas?

Here's another one, it's number 2 right?

>>10627813
I just want to know what position you’re applying for, because that question has got to be literally 1st grade material.

>>10627817
>>10627817
Yup.

>>10627817
ja. warum ist das denn Deutsch, wenn du dich in Rumänien bewirbst?

>>10627814
lots of western European companies built factories to produce in Romania in the 90s. Many of them also built R&D and distribution centers, so you will many postitions.

>>10627817
I’m convinced you’re retarded if you can’t solve this. The amount of thinking required for this is miniscule

>>10627823
Ist eine deutsche Firma. Ich bewerbe mich auf ein Auslandspraktikum.

>>10627825
Thanks lad. Good luck with the interview.
>>10627826
Some people out there low-key struggle with abstract patterns even if they're otherwise smart senpai.
Someone pull up the 1 3 5 7 polynomial.

>>10627831
Thank you, I hope I get an invitation.
>>10627819
>>10627826
It's an internship and I have just never done a test like this before, so I didn't know which patterns I should look for. Also, there was a challenging math test, which is certainly more relevant since it's an engineering position

>>10627831
>Someone pull up the 1 3 5 7 polynomial.
what?

>>10627153
A function f is linear if and only if
a) f(a+b)=f(a)+f(b), and
b) f(k*a)=k*f(a)
for any a,b and any scalar k.
The concept also applies to higher-order functions (functions of functions), e.g. differentiation and integration are linear, Laplace and Fourier transforms are linear.

Is it okay to fail classes in college? I failed one and maybe two this semester and I'm extremely worried about the ramficiations of failing...

>>10627302
For a perfect inductor, yes. In reality, any physical inductor also has non-zero resistance, so the voltage across the inductor needs to be equal for the current multiplied by the resistance in order for the current to remain constant.

I really like electrical engineering, but where the fuck are all the internships?
I’ve applied to a few, but they’re all in power. I’m more interested in communications, but everything is in power which is boring as fuck. I’m pretty sure I’m not getting hired anywhere because at the interviews, I express more interest in signals than power.

If I want to study plasma physics in grad school, do I become a PDE wizard or what math beyond that do I have to study?

>>10627969
wat?

>>10628005
one or two or three is okay, just try not to fail any more (assuming undergrad)

>>10627763

I cant recall how many subjects that was (I guess that's what you refer as "units"?) but it was fairly standard for engineer studies in Poland. It was a serious problem for students wanting to work part time.

>>10627771

And yet there were people working part time (full was probably impossible) AND taking part in uni activities like science clubs. I always considered myself worthless for being unable to do anything else than those subjects. But in the end Im finishing phd right now so I guess Im not completely worthless...

I'm stuck with this autistic lab partner for the next month and he is noticeable impeding my progress. We have to work through about a dozen exercises, and this absolute fucking shitwit just won't work fast enough and constantly has to autistically check and manipulate our setup for no reason which just impedes it further. Had he simply been absent in our last prac I'd have done triple the fucking work we got done. I've already thrown him under a bus a few times by just taking over and doing the stuff I need to pass really quickly so he doesn't have time to copy off me because he has no idea what the fuck he's doing.

How do I approach our tutor about being able to work on my own from now on? I feel like they'll just give me some bullshit about how 'teamwork is a part of what you'll be doing in the rest of your career so you better learn!' and garbage like that.

Personally, I never understood the belief that energy can't go through a truly empty space. It makes sense to me with certain types of energy, but I don't understand why it seems like people believe it as an across-the-board concept.

>>10628265
numerical methods :V

>>10624788
academics please respond

why is being connected a necessary in brooks theorem? is it because of graphs like pic related or something else?

Would it be painful to end up in a black hole?
Is the process of being infinitely stretched out literally like being quartered or do you not notice it since you're inside the black hole?

Can the fourier transform be used to send multiple strands of data?
I know almost nothing about signal processing, by the way.

why integrate the area under a curve using rectangles when there's always a "gap" left at the top of a rectangle? Why not calculate the slope of the different y-values at the top of the rectangle to minimize the gap? Wouldn't this always lead to a better approximation? Please no bully, I'm self teaching.

>>10629396
The gap above the rectangles gets smaller as the rectangles get thinner. As their width approaches 0, the gap disappears. So the width is said to be a really small number, dx, as dx approaches 0.

>>10629396
We don't integrate with rectangles. We integrate with tangential slopes at every conceivable point. It's a fundamental aspect of calculus. For finite sums, many different methods are applied, including the trapezoid rule, which you suggested. This value can also be found by using both left and right values at the top of the rectangles, then averaging the two results. The reason we use rectangles is because, as the width of the rectangle approaches zero, it forms a single value, rather than two different values. An infinite sum of these infinitesimally small single values provides the most accurate sum.

We don't worry about minimizing the gap, because the limit already approaches zero. Just imagine cutting the rectangles into smaller rectangles. The distance between the two upper corners of the rectangles approach zero.

It's important to remember that everything in calculus is fundamentally based on the infinitesimal, which is the essence of limits.

>>10629396
>why integrate the area under a curve using rectangles when there's always a "gap" left at the top of a rectangle?
Using rectangles you can define two extreme cases, the underestimating (using the min of f in the interval) and the overestimating (using the max of f instead). However, in the limit of continuous rectangles both become equal and give you the "integral".

You can do as you say, use the slope, and still get the same value for the integral. The only difference between the three methods is how fast your approximation approaches the true value of the integral.

Someone please post some math/science book flowcharts.

chalkboard vs white board?

>>10629585
chalk if you're poor

>>10629549
pic

So I'm a beginner python user.
I'm trying to create a tree from a connect4 board. The root is the empty board and the children should be a tictactoe piece at the bottom most points of the board. Let's say the board is 8x8, then there should be 8 children with 1 piece each, right? When I wrote the code, by the 8th child all 8 of the bottom part of the board were filled. I don't get it. Each time I make a node, a new board is being made from the original board, right? Should I be thinking of them as pointers instead?

Can someone that studies physics help me?
I am taking a course in classical mechanics and we go to labs once a week. I've hated it so far, but I will have to put up with it for this course and for electromagnetism as well.
I want to change my way to look at those labs. Our prof wants us to get a good foundation on experimental physics and that sounded cool to me for the first time, but I feel like the reading material that we are given in the course doesn't go in enough depth and it certainly doesn't make it interesting.
We have covered stuff such as measuring, propagation of errors, making graphs, finding relationships using data and we write reports every week. It's there a textbook or any other resource where I can learn that kind of material, see what's to come and grow some liking for experiments in physics and being in a lab?
I am not majoring in physics by the way.

What does the electric field of a charged particle in uniform motion look like? Also, since any changes in the field propagate as a wave at the speed of light, doesn't that mean the particle is radiating some energy even though it's not accelerating? Wouldn't this slow down and stop the particle even though it's not interacting with anything?

Which law is this? Or who came up with it? I see it in my text book, but it doesn't say who like Gauss or whatever.
E= -dV/dx ?

>>10629902
Could this pdf, in theory, be used to self-teach abstract algebra? Or is it all just modified mathgen gibberish?
I'm honestly baffled this exists, and there is at least one printed hard copy in the world, and it belongs to a minecraft rapper math prodigy on 4chan?

>>10629726
>Each time I make a node, a new board is being made from the original board, right?
no
>Should I be thinking of them as pointers instead?
yeah

You need to copy the board, you do that like this:
board_copy = board[:]

>>10630088
You can think of it as another definition for / a way to calculate the electric field. The electric field at a point is the negative derivative of the electric potential at that point, if we're considering essentially 1 dimensional situation where the potential only depends on the x-coordinate.
In 3 dimensions the electric field would be the negative gradient of the electric potential.

how do I into undergraduate math research?
I don't think anything I produce will be of publishable quality

Do I need a lot of research experience to get into a phd program in the US? I will have one or maybe two semesters by the time I apply and it is the only part im worried about as my grades and GRE scores are good. I am in EE and only have so little because didnt even think about going to grad school until last year. Domestic student and focusing on optoelectronics and photonics if that matters

Please help.

>>10630123
If it's another definition for a way to calculate electric field, it must have been derived from some other equation. Maybe Farday's law of induction?

>>10630394

>solve x^2 - 6x + 8 = 0
>x = 2, 4

I get why x=2, but why is it also 4?

>>10630402
Every conservative vector field (like a static electric field) has a corresponding potential field such that the vector field is the negative gradient of the potential (this is a result from vector calculus / real analysis). Thus we know the potential field exists and the formula makes sense.
If you're looking for physical interpretation and derivation of the formula, I think Young & Freedman's University Physics has it. It first defines the electric field normally (via the electric force on a test charge), and later explains electric potential. Electric potential at some point is the work done on an unit charge as it's brought to that point from an infinite distance (work must be done on the charge as it moves through the electric field). After defining electric potential this way, it's easily shown the formula applies.
So only Coulomb's electric force law is required to derive it.

>>10630490
>solve x^2 - 6x + 8 = 0
for simple quadratics like that you want to find multiples of a*c that add up to b
so:
a*c = 8
multiples of this are 1 and 8, 2 and 4, -1 and -8, and lastly -2 and -4
now which add up to -6?
-2 and -4
this means you can factor the original quadratic into the following:
(x-2)*(x-4) =0
from this you can see x = 2 and x=4 are the only values for x that will give you 0

>>10630422
So pretty much after integrating, I get H2pi*r, so then I divide current over 2pir?

>>10619111
Suppose we have
[eqn]\hat{H} = \frac{1}{2} \left( -\frac{\textrm{d}^2}{\textrm{d}x^2} + x^2 \right) + V(x) [/eqn]
such that
[eqn]
V(x) =
\begin{cases}
-\frac{1}{2} & |x|\le \varepsilon\\
0 & |x|\gt \varepsilon
\end{cases}[/eqn]
If we were to try to find a [math]\Psi_n[/math] such that [math]\hat{H}\Psi_n = E_n \Psi_n[/math] the way we do in the case of, say, particle in a box, we'd find that there is no solution, because the inner interval solutions [math]E^{i}_n = n[/math] and the outer interval solutions [math]E^{\pm}_n = n + \frac{1}{2}[/math] would never have a common [math]E[/math].
That would mean that the Hermite Polynomials are not exhaustive if we do not demand analytic solutions on [math]\mathbb{R}[/math], but instead piecewise analytic solutions on [math](-\infty,-\varepsilon), (-\varepsilon,\varepsilon), (\varepsilon,\infty)[/math]. Maybe I'm blind but I can't find shit about this.

Brainlet who needs help studying for exam in signal processing
Please give info and sites for things I posted below

frequency response
* spectrogram
* Chapter 4: Frequency-Domain Analysis: the z-Transform
z-transforms
* convolution and the z-transform
* inverse z-transforms, partial fraction expansion
inverse z-transforms, partial fraction expansion
Ch 5: Design of Nonrecursive Digital Filters
Ch 6: Design of Recursive Digital Filters
* feature extraction
* dynamic time warping
wavelets

>>10629292
What I never understood with the last explanation of something in String Theory I saw:
>If you set an atom in motion 1 way, the 1 next to it sets in motion the other, and keeps moving that way, therefore always connected

How does that show more than they set in motion that way?

>>10630655
what the fuck does a string theory book do talking about atoms in some undefined relation to one another moving?

>>10629438
>>10629439
>>10629441

thanks gents

Does an undergraduate degree in electrical engineering prepare one at all to study machine learning in grad school?

>2kg tomatoes = 1kg ketchup
how is this possible

>>10630736
ketchup is more dense than tomatoes

>>10630731
no, unless you tailor your electives around CS/machine learning
if that is even possible at whatever uni you attend

>>10630736
less water

>>10620581
I feel you on the anxiety, but the algebra skills are the real problem. bone up, mate. lose your ego.

>>10630638
Hello

>>10630371
anyone that can help a retard out?

>>10629917
you an eng major?

>>10619111
how many degrees of freedom does this system have?

>>10631041
I would say, two: displacement in the x axis and displacement in the y axis, but I don't know

Really dumb question: Is biophysics related to genetics at all? Are there any biophysicists trying to figure out how DNA molecules work so we can edit them directly?

>>10626152
You aren't a person anyway-

What's the best stem major for a brainlet?
EE?
Biology?

>>10631203
psychology

how do i ask a professor about research opportunity as an undergrad through email? is there a good template to follow? it will mainly just be for at least two semesters and for two courses worth of credit, but will help with grad school applications if i go for that later on and if i like it i will stick with it for longer than 2 semesters

>>10631228
>psychology
>stem

>>10631044
I'm fairly sure it's implied that both the wheel and the mass are constrained to the vertical axis.

>>10619111
Me chinese
Me play joke
Me go peepee in your coke

Would it make sense to do this?
You buy a 2 items for $12, thus spending $24.
You sell the items for $15 each and after taxes, you get $29.1
Finally, you buy 2 of the same items for $14 each, thus spending $28.

Do you make profit off this? Is it logical to sell the items for high, but re-buy at a higher price, but lower than selling price? Do I just keep the items after buying at $12?

>>10631547
I know it's a weird question. Typically I buy something for $14, then re-sell at $15. Rinse and repeat.
Encountered someone who sold at $12. I do want to use these items, but if reselling then buying at higher price will still net me profit, I'll sell so I can buy more in the long run

>>10630736
lol

How would I go about calculating the number of smaller circles that can fit on the circumference of a bigger circle?
assuming the circumference of the bigger circle passes through the centers of the smaller ones, and that I know the smaller circle's radius.

why is P = NP even a thing? To me solving and verifying seem to be almost completely unrelated. This problem seems thoroughly malformed and undecidable.

someone can help me solve 33b?

Very stupid question here regarding signals.

Parsevals theorem explains how to calculate the power of a signal. But what does the power of a signal even mean? I know how to calculate it but I have no idea what it means. I have no intuition of what it means. Anyone with a big brain out there who can shed some light?

>>10631732
You can get a lower bound approximating the curve inside each circle as 2*R. Then, for the Radii that you defined, check if the circles would fit.

>>10631812
nvm i figured it out, i just don't understand why they listed positive interval as [0, 33] when it's (0, 32.5)? is there something im missing? -4x^3+130x^2 is positive for (0, 32.5), right?

Why is this the formula for standard deviation? Wouldn't it make more sense to just take the sum of the diferences from the mean (as positive values) and dividing by n?

>>10631938
Least squares works, least moduli doesn't. SD is used instead of mean deviation for consistence.

>>10631238
I always did this in person instead. Email is scary.

>>10631766
>To me solving and verifying seem to be almost completely unrelated.
Think of it like a non-deterministic module producing every choice at once and a deterministic module filtering out the invalid results. Note that polynomial time verification is only one way to characterize NP.

>This problem seems thoroughly malformed and undecidable.
The general consensus seems to be that, if it's provable either way, none of our current proof techniques are good enough to do so. They all fail in one way or another.

>>10631938
You can define a deviation however you want, and call it "standard" for all anyone cares. It just turns out that this way to measure "deviation" turns out to have some nice theorems attached to it.

Any material equations for how the electric conductivity of a material at some point depends on the mechanical strain at that point? I'd like to find a simple model that works for some real materials for a start. Any books dealing with this subject would be great.

>>10631732
Angles. tan(π/2n)=r/2R => n=π/(2asin(r/2R)). The sector (wedge) occupied by each small circle can be split into two isosceles triangles with sides r,R,R, angle π/n. This can be split into 2 right-angled triangles with angle π/2n, hypotenuse R and opposite r/2, thus sin(π/2n)=r/2R.

Note that for small angles, sin(x)~=x => asin(r/2R) ~= r/2R => n ~= πR/r = 2πR/2r, i.e. the circumference of the large circle divided by the diameter of the small circles.

>>10619111
but shimura goro is still alive

looking for a nice background picture.

>>10630552
Reality is analytic anyways

>>10632366
anon i...

This might be really stupid.
I am working on the sugars in berries. I think that a good equation to represent it is a sigmoid function of temperature multiplied a logarithmic function of time.

I am positive about the sigmoid function. The problem is that using a logarithmic function doesn't seem like a good way to represent how the sugar content plateaus after a while. Though I guess it's a good enough approximation of what happens.

>>10631203
computer science or mechanical engineering, nursing, general biology with the intent of teaching at a low level

Doing some calculus and drawing some solids to find the volume of. Anyone got any tips or tricks for drawing convincing figures?
Curvature (e.g. a sylinder with a "bowl" for a top) is kind of hard to do justice.

>>10632419
ohhh... i see

What's better, 90% chance to get 1, or 50% chance to get 2? (assuming you get a thousand "tries" and can keep everything)

>>10632508
true college thoughts

>>10632508
You get 900 1’s or 500 2’s

>>10632435
Mech e is the hardest engineering tho

>>10632451
I just draw bad figures and imagine the shapes.

>>10632434
I think you "logistic growth, calculus" is what you're looking for.

>>10631921
no one knows?

>>10631921
Yes.

>>10632618
then why in the solution they wrote
>on the interval [0, 33] x [0, 21000]
what is the point in even stating [0, 21000]?

>>10630854
Yup, but I still feel like I can learn useful and interesting stuff in those labs with the right mindset. Do you have any suggestions?

>>10632565
I will look it up, thanks.

>>10632659
The interval you got is a subset of the estimated interval they are proposing, if the solution is in yours then it's also in [0,33]. Same with [0,21000], the real maximum isn't 21000 but it's just an estimation to give you an idea of where your solution should be approximately. If they are explicitly saying that [0,33] is THE interval where f is positive then that's legitimately wrong, but if they are just saying that the interval where f is positive is within [0,33] then there's nothing wrong.
>what is the point in even stating [0, 21000]
Your task isn't to find just a single number, it's to find the GirthxLength value, so you need the two values to give a proper answer. The value you are looking for is there, I guess it's just as a clue.

>>10632414
it's not like you can't have analytic potentials that basically are discontinuous up to a small, local pertubation.
The particle can't just go poof like that

>>10630718
It was some PBS thing
Stuck in my head because I thought it was a weird thing for them to say.

>>10632964
yeah it sounds like a non sequitur

>>10622254
You are dealing with LINEAR differential equations. So they can be written D(y) = ... where D is a linear combination of differential operators. First lets talk about the homegenous case when D(y) = 0.

Say y'' + y' + y = 0. Then this can be written D(y) = 0 where D = d^2 + d + 1. Now notice this fact. D(ay) = aD(y) where a is constant. And D(y+z) = D(y) + D(z). This is critical. It means that if S and S' are two solutions, D(S) = 0 and D(S') = 0, then any linear combination of the form aS + bS' is also a solution because D(aS + bS') = D(aS) + D(bS') = aD(S) + bD(S') = a0 + b0 = 0. Thus the solutions to the differential equation form a vector space of functions. This space has a basis, some solutions S1 through Sn, such that any general solution can be written as a linear sum of the basis solutions.

Now consider the inhomegenous case y'' + y' + y = f. D(y) = f. To solve it in general we need two things, a particular solution to D(y) = f, say P so D(P) = f. Then note that if S is a solution to the homogenous case like before then D(P + aS) = D(P) + aD(S) = D(P). So P + aS is also a solution. We can generate all the solutions by adding the homegenous solutions in.

Note all this follows from some linear algebra. Look at how systems are solved there. It's the same theory.

Could someone explain the
>What is outside the edge of the Universe?
question? Why do people act like it can't just be void?

>>10632659
I don't know. Maybe to give you a heads up that your function is correct or not. Did you solve the question algebraically?

>>10633030
Because their brain is void

If photons have momentum does that mean if enough light hits someone, they'll stumble or feel a push?
Can I build a more powerful version of https://www.youtube.com/watch?v=-vgNh3fLxJc and fuck with people by making them stumble with light?

>>10633514
youd light them on fire before you pushed them

>>10622511
Just took a midterm on Diff Eq... Explanation was surprisingly helpful

If a clock pulse is needed to generate a frequency of 5.64 kHz with a duty cycle of 60%, what must be the resistance values of R1 and R2, assuming C1=0.022 uF?

I used the formulas for duty cycle regarding high and low times with the known period, plug them into the formula for the known frequency and came up with R1= 2.33k ohms and R2= 4.65k ohms.

Just looking for a second opinion to make sure I went about it the right way and didn't miss something simple or over think the problem.

>>10633063
no, you are suppossed to draw a graph then to look up the answer from there. i guess that's why
>>10632763
desu thanks

>>10633514
If you hit someone with enough photons to move them they'd be incinerated

Would it look autistic to grad school if I retake a class that I got a C in to replace the grade with an A?
it is my only grade near a C and is technically in my major (probability & statistics class), it would increase my GPA by 0.05

>>10634236
also I only did so shitty when i took it because i missed a test or two due to skipping class too much and the professor not putting test dates online

>>10633553
For an astable using a 555? Those figures are correct. A frequency of 5.64kHz corresponds to a period of 177.3μs. 60% of that is 106.4μs, 40% is 70.9μs.

R2*C1*ln(2)=70.9μs
(R1+R2)*C1*ln(2)=106.4μs

>>10633552
That's great, anon. I hope you did well.

>>10634236
I had no idea you could retake classes in which you got a C. Are you from the US? That would explain why most of you come here showing off you near perfect GPAs.

>>10634282
it depends on the university policy really, it doesnt actually replace the grade but averages the two and uses that for GPA. It still shows both grades on the transcript though, so anybody could tell if you just took all your classes multiple times to get a perfect GPA.
I have a full tuition scholarship so it is no cost to retake, but most would not retake as long as they pass because of the cost and one grade isnt that important for graduating.
Grad school applications are a different story but i still dont know if they will view it as a bad or good thing to take it twice. What is even worse in my opinion is some schools give 4.333 GPA for an A+ while others dont, so people can not have all As but have a perfect gpa on paper

>>10634282
>>10634301
also my school limits grade replacement to 2 classes (~6 credits) out of the 120-134 credits you need for a degree

As someone with no background in engineering is Optoelectronics going to be good investment to study or just a meme and how should I prepare if I want to pursue the study of it?

>>10634264
Yes, thanks anon! That's what I had computed

Can somebdoy help me please, I tried approaching it from different angles and I could never get this answer.

Does stacking several corpses in a single crematorium increase the rate at which corpses are being incinerated? How could I calculate de rates based on number of people cremated at once?

For example, a single person might take 2 hours. Maybe if you have 2 it will take 3 hours (decreased the rate to 1.5h each), if you have 3 corpses it might take 4 hours (1.33h each), etc. How could I find about this, other than incinerating corpses myself (I don't have any so I can't do the test).

>>10634836
Is this /pol/-related?

>>10634877
Yes, I read them every now and then. Apparently they believe the Holocaust couldn't have happened because of the time required to incinerate corpses if you do it once after another. I've done some researching and nazis actually cremated more than one body at once to save time. I'd like to do calculations based on that, I think it could disprove Holocaust denial.

>>10634932
All these things should have already been explained at length in actual, canonical literature.
Like, none of the internet shit. Because last time I checked some things tinfoils "debunk" have never actually been claimed by anyone.

How do you graph a polar plot with complex solution?
I'm curious about how r^2=2cos(2θ) looks like.

>>10635537
you can always look at Re and Im individually

>>10634836
When I was there we were told that the nazis threw in four to six people at a time, and that many times they didn't kill them first. Nevertheless, whether or not <number> could be burned in such an efficient manner, doesn't really prove or disprove anything, does it?

>>10635537
r is either real or imaginary, so you can just graph the two cases separately in different colours.

Sorry for bloggposting but I don't want to go to /adv/. Is there any uni in the UK, that hosts a CS bachelor that focuses on math and phys stuff/electives? From my miniscule search, most of them focus on the software and business side, which is not what I want and got me panicked. I want to dive deep in cs, tcs and anything math, phys since my background is related (almost got a degree in matsci). There is only one uni in my country that provides that but I will probably fail at this year's general exams to access it (maybe I'll try again next year). Again, sorry for bloggposting.