/sqt/ /qtddtot/

[Anonymous No.10446589]

Questions about computers go on /g/. Questions about /diy/ go there.

I've just noticed that we've been skipping the "not" and it should be /qtdndtot/ edition.

[Anonymous No.10446592]

Scientisticially speaking, how do I cure my autism?

[Anonymous No.10446596]

>>10446592
Autism naturally goes away once you've built enough muscle.

[Anonymous No.10446745]

[math]F(x,y) = \left< 3x^{2}-2y^{2}, 4xy+3 \right>[/math] is a non-conservative vector field, right?

[Anonymous No.10446756]

>>10446596
How can I build muscle if I can't build muscle? I've tried everything

[Anonymous No.10446763]

>>10446745
If unlike my biceps its curl is non-zero then it is non-conservative I guess.
Why can't I build muscle?

[Anonymous No.10446852]

I'm trying to solve this problem using a smith chart.
First I divide the 52/37 to get my normalized impedance and I plot that on the chart.
Then I get stuck. Any ideas? I figure I need to find b*l where b = 2pi/lambda, lambda = up/f, and up and f are given. up is phase velocity.

[Anonymous No.10446923]

Can someone help identify what I did wrong? First I normalized the load impedance and plotted that on my smith chart.
Next, I found the wavelength towards the generator, .1667, and traveled that distance clockwise. Found the normalized impedance at the input, then multiplied it by the line impedance to get the input impedance.
Plugging in that value for the Vin equation, I get the answer in the picture. Apparently it's wrong. I tried doing the calculation without the smith chart and I arrive at a somewhat similar answer. Any ideas?

[Anonymous No.10446937]

>>10446763
you don't eat enough or you don't go hard enough
most likely the first

[Anonymous No.10447086]

What are the best universities in Europe if I want to pursue a Masters or PhD specializing in Optics/photonics/lasers etc? Mostly interested in Italy, France, Norway, Austria, Germany

[Anonymous No.10447124]

>>10446589
How does one make anime girls real and more importantly, love me.

[Anonymous No.10447564]

How would you go about solving a (parabolic?) PDE
[math] u_xx + f(x,t) u_x = 0 [/math],
where [math]f(x,t)[/math] is a known function. There are also Dirichlet boundary conditions for [math] u [/math]. However, there is no initial condition, would I need some kind of an initial [math] u_0 [/math] to get a solution?

[Anonymous No.10447567]

>>10447564
Fuck I made a typo. The first term should be [math] u_{xx} [/math].

[Anonymous No.10447737]

Can someone explain the step taken here?
how do they remove 1/h and get -1/x(x+h)

[Anonymous No.10447744]

>>10447737
Nevermind i got it.

[Anonymous No.10447850]

I watched a couple of youtube videos that explained why the sky can be blue or red. They were clear and convincing.
But I'm not sure I understand why there are ray in certain wavelengths that don't seem to scatter like the others. For example, green. Why doesn't pic related include green in that beautiful spectrum of colors it shows? Why does it jump from blue to yellow, avoiding green?

[Anonymous No.10447866]

>>10447850
Made quick shoop to illustrate how it should supposedly look like. Why isn't it like this?

[Anonymous No.10448429]

Which programing language should be a good start for a computer retard like me?

[Anonymous No.10448476]

>>10448429
python is an easy one and is useful in many fields

[Anonymous No.10448484]

>>10447086
anyone

[Anonymous No.10448536]

I'm trying to calculate the absolute error between two angles, a and b, given cos(a), sin(a), cos(b) and sin(b).

I know a simple approach is to just find the angles first by taking the inverse tangent and then taking the minimum of (|a - b|, |a - b - 2pi|).

I would like to find a way where I don't have to take the minimum, but just find the absolute error in one expression. Can someone tell me if the following approach would work?

a - b = atan2(sin(a-b), cos(a-b))

With

sin(a-b) = sin(a)cos(b) - cos(a)sin(b)
cos(a-b) = cos(a)cos(b) + sin(a)sin(b)

Any help would be much appreciated!

[Anonymous No.10448682]

>>10448484
You need to find this answer yourself. It doesn't seem very difficult to do either, it's not like being a leading institution in a particular field is a closely guarded secret.
Browse through publications and see which universities pop up. Look at the department websites and compare the curriculum.

[Anonymous No.10448742]

>>10448536
That would work. Or you could also use
cos(a-b)=sin(a)*sin(b)+cos(a)*cos(b)
=> |a-b|=acos(sin(a)*sin(b)+cos(a)*cos(b))
acos() returns an angle in the range [0,π].

One downside to this approach is that it's ill-conditioned if |a-b| is very small. sin(a+ε)*sin(a-ε)+cos(a+ε)*cos(a-ε) ~= sin^2(a)+cos^2(a)=1. And acos(x) is ill-conditioned for x~=1. In the worst case, rounding error might result in e.g. acos(1.0000000001) which will give you a domain error.

The atan2() approach is more work but is also more stable. atan2() should only fail if both arguments are exactly equal to zero, and it's only inaccurate if both arguments are very close to zero. In your case, the argument pair is a point on the unit circle.

[Anonymous No.10448785]

>>10448682
I have done some searching, just wanted to know if any euros have heard of good universities for it that I may have missed. I will keep searching and browse publications though

[Anonymous No.10448882]

>>10448742
Awesome! Thanks so much for the detailed explanation! I'm working on a deep neural network that predicts dihedral angles in protein structures and I'm somehow getting conflicting results in the mean absolute errors between the two methods I described. I'll see if I can find where I'm screwing up tomorrow

[Anonymous No.10449022]

How long do I need to sleep to be effiecient ?

[Anonymous No.10449102]

Lets say I have some f(x1,...,xn) = g(x1,...,xn),
f,g: Rn -> Rn

How would I find g^-1(f(x1,...xn))? It should be impossible based on the dimension right?

[Anonymous No.10449154]

>>10449102
> Lets say I have some f(x1,...,xn) = g(x1,...,xn),
> f,g: Rn -> Rn
Do you actually mean that the two functions are identical?
> How would I find g^-1(f(x1,...xn))?
If f=g => g^-1=f^-1 => g^-1(f(x1,...xn))=f^-1(f(x1,...xn))=(x1,...xn).
> It should be impossible based on the dimension right?
No. If the function is R^n->R^n, it may be invertible, at least over specific regions even if not over the whole of R^n. If it's R^n->R^m where m=/=n, then it can't be invertible.

[Anonymous No.10449183]

>>10446852
>>10446923
bump

[Anonymous No.10449189]

>>10446589
Why do female feet smell so good? Is it phermones?

[Anonymous No.10449409]

>Talking to my girlfriend today
>We start talking about little silly things we did as kids
>I find out that, like me, she use to lick 9 volt batteries out or curiosity
>She also tells me that there are memes suggesting that other people also have did the same thing

I'm curious as to what compels people to do really odd things such as thing.

I mean it's not like I was pushed into doing it, and it's not like I had any reason to think the 9 volt battery was appetizing, yet I still did it and so have others.

Scientifically why do human being do things like this?

[Anonymous No.10450243]

Where can I find phase diagrams of various fluids under a vacuum, I can find ones for water, but I'd like to have some of other common fluids as well.

[Anonymous No.10450470]

Is there a calculator/solver that lets me input a predicate statement and a signature, outputting an equivalent statement, but only using the symbols from the signature?

[Anonymous No.10450506]

>>10449409
low iq

[Anonymous No.10450526]

>>10450506
This, I never did this and I have superior IQ

[Anonymous No.10450573]

>>10450506
This, I used to do this and I have low IQ

[Anonymous No.10450592]

>>10450506
This, I only did this a handful of times and I have medium IQ

[Anonymous No.10450598]

>>10447850
idk, but see this
https://en.wikipedia.org/wiki/Green_flash

[Anonymous No.10450643]

What's the /sci/ equivalent of a /g/ battlestation?

[Anonymous No.10450649]

>>10449409
Curiosity. It's an instinct that has helped us dominate the planet and the cost is that a percentage of us die due to trying dangerous shit.

[Anonymous No.10450674]

I read some ”pseudo”science i dunno about how aluminum foil is bad for you because it leeches into food and whatnot binding to proteins and causing dementia
I thought the kidneys got rid of any metals? Can i still eat burritos without killing my brain?

[Anonymous No.10450697]

Find a dimension of linear span formed by vectors [math]$x_1 = (1, 0, 2, -1), x_2 = (0, -1, 2, 0)$[/math]. Show that [math]$x_3 = (1, -1, 4, -1) \in L(x_1, x_2)$[/math].

I made a matrix with rows as vectors. Since it's 2 and both vectors are not a linear combination of one another, rank is 2 and dim(L) = 2. But how do I show that x_3 is in that subspace?

[Anonymous No.10450749]

why isnt hydrogen used a fuel?

lets say there is a nuclear power plant with power output of ~1 gigawatt, how much hydrogen could be produced with that energy using electrolysis? surely it must be cheaper than paying arabs for their oil, fighting in their neverending wars etc. Build several of these plants/reactors to minimize costs, create jobs and skilled personnel, also develop and improve existing technology.

[Anonymous No.10450757]

>>10450749
Would it be possible to initiate an electrolysis reaction with a natural gas generator and then switch over to burning hydrogen to sustain the reaction while producing electricity, with the main fuel source being water? Or could you not produce enough hydrogen to sustain it?

[Anonymous No.10450769]

>>10450697
x_3 = x_1 + x_2

[Anonymous No.10450771]

>>10450757
no thats not possible, thats why I suggested nuclear, nuclear is the most affordable and clean energy source and hydrogen would be used as energy carrier

[Anonymous No.10450772]

>>10450749
Electrolysis is highly inefficient for mass production

[Anonymous No.10450774]

>>10450749
>why isnt hydrogen used a fuel?

It has been attempted, and lots of research done into it however big oil I believe fucked it into smithereens. Long live capitalism!

[Anonymous No.10450777]

>>10446589
Anyone know a good set of books to study up on piezoelectricity? Preferably something a little more basic as I've been out of the physics game for a while now. I'm looking at getting more involved in materials work and strain-based materials are the most interesting to me.

[Anonymous No.10450792]

>>10450757
Here's my retarded idea

[Anonymous No.10450804]

>>10450771
>>10450792
Ah I didn't see this before I posted, nvm

[Anonymous No.10450805]

>>10450792
no, that cannot work, this isnt some free energy thing, its not free hence the need for massive amounts of energy from nuclear, but its cheaper than than getting into foreign wars and spending trillions on literally nothing, instead of spending trillions on research on better nuclear, better hydrogen production, investing all that money locally in the country than pissing it away on arabs

[Anonymous No.10450809]

>>10450805
Well would your design be energy negative as well? You're spending energy to pump H around when you could just serve the grid with fission power and use batteries for everything. Unless there's something I don't understand.

[Anonymous No.10450814]

Damn, I am dumb. >>10450769
So, if a vector is not a linear combination of another vectors, then it's not in the subspace? Should I then create a matrix and check its rank?

[Anonymous No.10450816]

>>10446589
Hi /sci/ I have a question!

The context goes as following:
"
In a 3-person group, the number of possible relationships is 6
In a 4-person group, the number of possible relationships is 25
In a 6-person group the number of possible relationships is 301
"

Now a nice /sci/tizen helped we see that these are stirling numbers. However! I see from the matrix of Stirling numbers of the second kind that you get 301 from the [7, 3] (StirlingS2[7, 3])

My question is then, shouldn't it be group of 4, 5 and 7? Since on the Stirling matrix,

[4, 3]= 6
[5, 3]= 25
[7 ,3]= 301

Thanks in advance,

T. brainlet

[Anonymous No.10450832]

>>10450809
pretty much everything is energy negative, so yes.

Batteries are good but I think their production relies on stuff like lithium which is not widely available and also mining is damaging to the environment. Also can be a pollutant

[Anonymous No.10450836]

>>10450814
>So, if a vector is not a linear combination of another vectors, then it's not in the subspace?
Yes.

>Should I then create a matrix and check its rank?
Yes, if the new row is not in the span of the old rows, the rank will increase by 1.
https://en.wikipedia.org/wiki/Augmented_matrix

[Anonymous No.10450893]

>>10446589
Is bioinformatics a meme?

[Anonymous No.10451065]

>>10449154
I wrote that terribly. For some “an” and “bn”, f(a1,...,an)=g(b1,...,bn). I’m trying to find the mapping of an to bn.

However, my functions f and g are Rn->R. Based on what you said I cannot invert g, so my next approach is to find some other function with similar equivilancy to invert instead of f and g.

[Anonymous No.10451169]

>>10450816
What do you mean by a relationship?

[Anonymous No.10451192]

>>10451169
A person talking to another person I assume (no clear definition given).

[Anonymous No.10451311]

>>10451169
a pair engaged in anal sex

[Anonymous No.10451533]

>>10446852
>>10446923
Bump

[Anonymous No.10451616]

Brainlet Intro to Physics question here.

So, the attached image show the equation for the electric field at any point for both an infinite plane and an infinite piece of string.
Now, for a plane the field is constant throughout all of space, and I assume it is because as you move further away, the field due to points that are further away grow because of the angle to them increasing to.
BUT, for a string, it does depend on the distance from it, despite the fact that the same idea should still apply, with point charges on the string that are far away having a higher influence the further away you move from the string.
What am I not seeing?

[Anonymous No.10451676]

>>10451616
You can think of more intuitive arguments but write gauss' law for both cases. In the first the total charge density goes like 1/(L^2) and in the second it goes like 1/L. In the first it will cancel out the effect with the 1/(r^2) from the electric field and in the second will only cancel out 1/r, leaving one similar term.

In other words, in the first case, the further out you go, the less influence charges have, but there are more of them, in the second case same thing but the charge doesn't increase fast enough for the field to stop fading. Hope that helps a bit

[Anonymous No.10451711]

How the fuck do you factorize
-2x^2 - x + 6 ?
i know you split the middle into
-2x^2 - 4x + 3x + 6
and then
-2x(x+2) + 3(x+2)
but then what? (-2x+3)(x+2)?

[Anonymous No.10451729]

>>10451711
yes

[Anonymous No.10451743]

What's the formula (or what ever the right word is) called that's used to calculate z given that I know the values of x and y in:

x*y^1 + x*y^2 + x*y^3... + x*y^64= z

I know this is pretty basic since I remember going through it at school but can't remember the actual formula more

[Anonymous No.10451744]

>>10451729
i struggled with that shit for 10 minutes until i wrote it down and posted, and it just made sense

[Anonymous No.10451746]

>>10451743
formula any more*

[Anonymous No.10451791]

>>10451676
Oh wow, that was surprisingly easy. Of course with an extra dimension to play with you will have more electric fields. God that was stupid, thanks a lot man.

[Anonymous No.10452270]

>>10450749
> why isnt hydrogen used a fuel?
It is ... in very specialised circumstances, e.g. manned space vehicles/stations use hydrogen+oxygen fuel cells; mostly because they produce pure water as a by-product.

Other than that, there isn't much point. It isn't a primary fuel (i.e. it doesn't occur in nature). The primary method of production is from hydrocarbons; converting them to hydrogen consumes energy and produces a fuel with less energy (and much lower energy density) than the original hydrocarbons.

It's inconvenient to store. It leaks out of anything as the molecules are so small. It embrittles most metals it comes into contact with. Liquid hydrogen tends to create a lot of ice when evaporated.

Electrolysis of water isn't practical. It requires far more energy than is present in the resulting fuel, and produces atomic hydrogen (individual atoms, rather than H2 molecules) which is quite corrosive.

If you're looking to convert other forms of energy into chemical energy for ease of storage, ammonia is a better option.

[Anonymous No.10452281]

if being sick makes you lose more calories why can't fat people just try to get sick all the time
*gets nobel prize of medicine*

[Anonymous No.10452571]

>>10446589
How are really small amounts (nanograms and lower) of substances weighed out? For example botox's lethal dose is measured in nanograms and botox procedures are very common yet deaths from it are very rare. How does it get measured so precisely?

[Anonymous No.10452863]

When matching loads with an impedance matching circuit, when are shunt elements in parallel or series?

[Anonymous No.10453341]

Solving x^2 + 5x + 6 using the quadratic formula gets you (x - 2) (x - 3)
But solving by factoring gives you (x + 2) (x + 3)
What's the wizardy?

[Anonymous No.10453347]

>>10453341
>gets you (x - 2) (x - 3)
It doesn't

[Anonymous No.10453357]

>>10453347
>It doesn't
yes it does

[Anonymous No.10453373]

>>10453357
No it doesn't. That graph doesn't show what you think it's supposed to show. Relearn how to use the quadratic formula while factoring quadratics and pay close attentions to the signs this time.

[Anonymous No.10453385]

>>10453373
What am I doing wrong you faggot

[Anonymous No.10453390]

>>10453385
God you're annoying. Just relearn this shit from scratch

[Anonymous No.10453398]

>>10453390
Quit giving me meme answers
The zeroes are (x - 2) (x - 3)
Why do you get (x + 2) (x + 3) when factoring?

[Anonymous No.10453402]

>>10453398
>The zeroes are (x - 2) (x - 3)
No they're not. You don't know what a zero is

[Anonymous No.10453409]

>>10453402
>In this section, we will learn how to find the root(s) of a quadratic equation. Roots are also called x-intercepts or zeros.
It literally says the roots are (x - 2) (x - 3) in >>10453390

[Anonymous No.10453415]

>>10453409
Goddamn. A number a is a zero of a polynomial f(x) iff f(x) = (x - a)g(x) where g is another polynomial.

[Anonymous No.10453425]

>>10453415
the zeroes must be -2 and -3
x + 2, x + 3 is just factored form

[Anonymous No.10453438]

>>10453425
The zeros are -2 and -3 so the polynomial factorises as (x - (-2))(x - (-3))

[Anonymous No.10453444]

>>10453438
I get it now thanks anon

[Anonymous No.10453450]

>>10453444
You're welcome anon

[Anonymous No.10453555]

How does this step make sense?

Question arises from taking linear perturbations in equations of motion for a fluid, products of partials cancel out but I can't figure out how to get to this?

[Anonymous No.10453558]

opened a source while bingeing wikipedia on astronomy, and honestly just took 1 sec to scroll through it for titillating images (on my 4th shot of vodka)
in that short amount of time i instantly noticed my last name is in the article (italicized, not bold italics like the headers)
i'm reading up on how the hell i could have noticed that in my state of mind. it's about a 6k word article source and i scroll-wheeled through it just to look for images to ooh and ahh at honestly

is it just my mind being subconsciously vain?

[Anonymous No.10453619]

>>10446589
How??

I'm thinking it should be cos(s*a) where a obviously is 0. But apparently not. how does this work out?

[Anonymous No.10453695]

I haven't worked in 6 months due to recent tragedy. Going back tomorrow, it's not even a 9-5 thing, and I clearly understand that I need to work so I don't starve, but I still have insane anxiety over it all despite having done the job for years prior and it not even being a hard job.

What do? Any good documentaries on amazon prime atm? It's usually all trash.

[Anonymous No.10453706]

>>10446589
Help me out here guys, what's a good way to learn optical mineralogy? What are some good resources?

[Anonymous No.10453922]

>>10453619
s/(s-2)^2 = 1/(s-2)+2/(s-2)^2
L^-1{1/(s-2)} = e^2t
L^-1{1/(s-2)^2} = t*e^2t => L^-1{2/(s-2)^2} = 2t*e^2t
=> L^-1{s/(s-2)^2} = e^2t*(2t+1)

More generally:
L^-1{1/(s-a)^(n+1)} = (1/n!)*t^n*e^at

Any rational expression whose numerator has lower degree than the denominator can be decomposed into a linear combination of terms of that form. If the roots are complex then you get sin/cos terms from e^ix=cosx+isinx (complex roots always occur in conjugate pairs; the imaginary parts will cancel leaving a real function of t).

If the numerator has the same degree as the denominator, polynomial division will produce a constant term and L^-1{1}=δ(t). If the numerator has higher degree than the denominator, you messed up somewhere, as L^-1{s}=d/dt.L^-1{1}=dδ(t)/dt which is undefined.

[Anonymous No.10453955]

How can I improve my surveying skills?
I don't want to end up submitting a paper and get rejected for someone had done this before.

[Anonymous No.10454514]

I struggle with something:
If you pull capacitor plates apart, the voltage increases with the distance and a charged object hanging on a string between the plates must have an increased angle of deflection, no? On the other hand the deflecting force weakens with increasing distance. So does the hanging object keep the same angle i.e. does the force that acts on the object stay the same if you pull apart the capacitor plates or not?

[Anonymous No.10454799]

i'm reading that charles platt electronics book and i just doin't get. apparently with the arrangement on that picture. apparently when pressing the A button a sudden fluctuation in voltage occurs and according to the book the current goes through a capacitor. if i move the resistor just before the A button, capacitor seems to charge up normally. what's going on? why is it matter which side i place the resistor on?

[Anonymous No.10454826]

How would I express the following using predicate logic: "All politicians take part of elections, but there exist some politicians that nobody votes for"?

[Anonymous No.10454840]

>>10454826
"There exists something that is a politician and that hasn't received a vote."

[Anonymous No.10454843]

>>10453922
Ohh, ofc... How did I even miss that. Thanks anon.

[Anonymous No.10454855]

>>10446589
Is china good for studying in?

[Anonymous No.10454858]

>>10454840
>"There exists something that is a politician and that hasn't received a vote."
So [math]\exists x(P(x) \land \lnot Q(x))[/math] ?

[Anonymous No.10454901]

>>10454799
>[A]pparently when pressing the A button[,] a sudden fluctuation in voltage occurs and[,] according to the book[,] the current goes through [the] capacitor
Correct, all the voltage is across the resistor at first and then diminishes as the capacitor charges up.
[math]9V *u(t) e^{-t/RC}[/math]

>[I]f [I] move the resistor just before the A button, [the] capacitor seems to charge up normally. [W]hat's going on? [W]hy [does] it matter which side [I] place the resistor on?
So you swapped the resistor and capacitor around? Then you are measuring the voltage of the capacitor instead:
[math]9V*u(t)(1-e^{-t/RC})[/math]

[Anonymous No.10454905]

>>10454855
Fuck no

[Anonymous No.10455083]

Where can I find a list of simple projects to do with python, divided by difficulty?
I tried project euler but the problems are focused on the math and I want something more practical

[Anonymous No.10455150]

>>10447564
Pic related

First, consider the identity:

xu_xx=D_x(xu_x) -u_x.

We then have that:

D_x(xu_x)=(xu_x/x)(1-f(x,t)).

After multiplying both sides of the equation by 1/(xu_x), we get:

u_x=(1/x)exp(int(1/x')(1-f(x',t))dx'

Integrate again to obtain the general solution.

[Anonymous No.10455245]

>>10447564
After reading the follow-up comment you posted, I believe that the best method by which to derive a general solution is to use Fourier Transforms.

Let u(x)=int(dy u(y)exp(2ipixy)); moreover define u_xf(x,t)=g(x,t). The resultant PDE after substitution is:

-4piy^2u(y)=f(y,t)u_y.

The general solution reads:

u(y)=exp(-4pi int(dy y^2\f(y,t))).

All that must be done to derive the corresponding solution in the basis of x is to calculate the transform of f(y,t), substitute into the expression above, and then calculate the integral over y.

[Anonymous No.10455352]

>>10446589
Because the not gets absorbed into don't
>>10446592
Suicide
>>10446745
Integrate along the paths (0,0) to (0,1) and along (0,0) to (1,0)
>>10447124
Suicide
>>10447564
Method of characteristics
>>10449022
As many as you feel rested
>>10449102
Such a general question is impossible to answer. inverses need not exist. They exist locally for differentiable functions . g need to be bijective to exist
>>10449189
Soap
>>10449409
Low iq
>>10450470
Your brain, hopefully
>>10450506
Damn first thing I thought of too, literally same answer
>>10450643
Bookcase filled with high level textbooks, pic related is what you'd expect (needs bookcase tho)
>>10452281
Fat people ARE sick

[Anonymous No.10455394]

>>10455352
Seek help

[Anonymous No.10455496]

>>10446589
I've never understood how sine works. I know it's a wave function, and I know its uses in trigonometry, but nobody in school has really explained to me what it is, or how/why it can be used in so many different formulae.

[Anonymous No.10455519]

>>10455496
It's the solution to y''=-y with y(0)=0 and y'(0)=1
It's the inverse function to the integral: [math]\int \frac{1}{\sqrt{1-z^2}}dz[/math]
It's the odd part of [math]e^{ix}[/math] i.e. the linear combination [math]\frac{e^{ix}-e^{-ix}}{2}[/math]
It's the infinite polynomial/power series [math]\sum \frac{(-1)^{n} x^{2n+1}}{(2n+1)!}[/math]
It's -i*sinh(ix), cos(x-90°), 1/csc(x)

[Anonymous No.10455528]

>>10455496
sin(x)=x

[Anonymous No.10455531]

>>10455496
It's the solution to y''=-y with y(0)=0 and y'(0)=1
It's the inverse function to the integral: [math] \int \frac{1}{\sqrt{1−z^2}}dz [/math]
It's the odd part of [math] e^{ix} [/math] i.e. the linear combination [math] \frac{e^{ix}-e^{-ix}}{2} [/math]
Its the infinite polynomial/power series [math] \sum \frac{(-1)^n x^{2n+1}}{(2n+1)!} [/math]
It's -i*sinh(ix), cos(x-90°), 1/csc(x)

[Anonymous No.10456749]

>>10446589
My second semester will start soon and one module is named "simulation tool training". What can I expect to do there?
Just working with Matlab and Latex?

[Anonymous No.10456771]

>>10455496

[Anonymous No.10456786]

>>10451616
Another way: Try looking at field lines. They radiate outwards from the charges normally to the surface. The density of field lines gives the strength of the electric field. For a plane they all radiate away from the plane and do not diverge from eachother with distance because they are all parallel, and for the string they are not parallel and diverge as the travel radially away, but along any angle theta they are mutually parallel giving a 1/r proportionality, while for a point charge they diverge with respect to both polar angles theta and psi so the field is proportional to 1/r^2.
You will likely have to work with field lines soon in your class if you haven't already

[Anonymous No.10456789]

>>10455496

[Anonymous No.10456796]

>>10455496
lmao sohcahtoa lmao

[Anonymous No.10456852]

the fuck is an mfp /sci/, google ain't helping and I've never heard of this unit of distance before

[Anonymous No.10456890]

>>10453341
Bruh, (x-2)(x-3) is x^2-5x+6
you out of it

[Anonymous No.10456944]

Why aren't we extracting heat from air to produce hydrogen we can burn later?

Like heat pumps got COP over 5 and heat engines like 0.3, so if we get it, it's like you can with 10kW heatpump and heatengine coupled together correctly extract continously 5kW of heat from air to create a movement.

Why nobody works on this more?

[Anonymous No.10456994]

>>10456944
not sure I entirely understand what you're saying, kinda wandered off after starting with hydrogen; but heat engine efficiency would be far less due to low temperature difference?
also https://en.wikipedia.org/wiki/Carnot%27s_theorem_(thermodynamics)#Proof

[Anonymous No.10457030]

>>10456994
How big temperature difference is depends on the compressor, you can chain multiple, even use multiple heat engines in a row, to maintain it... Like if heat engine uses 10% of heat to convert to mechanics, there must be 90% of heat left, and you reuse that heat, I'm talking about lot of heat difference, not some tiny thing. Not used heat is pumped back into system. It's nothing like closed system or "thot and tcold" that is stated on the wiki...

[Anonymous No.10457040]

Anonymous 03/11/19(Mon)19:10:58 No.70128363▶
Anon, codemonkey who has never learnt stats here.
I have generated N random values that have exponential distribution with lambda=1.1 (using python's numpy). How do I prove using chi-square test that this variable has exponential distribution? If the distribution was discrete I could calculate expected frequency and plug right into the formula but what to do with continuous (exponential) distribution?

[Anonymous No.10457058]

>>10456852
ah fuck never mind I'm a dumbass. mean free path

[Anonymous No.10457094]

>>10457030
ok, I kind of understand. You're thinking of energy storage via this method. So your previous post mentioned a 10 to 5 ratio in to out, so 50% efficiency.
My question is, why not use something easier to pump, like water. And while we're at it, ignore the heat deal cause thats no good for long term energy storage, with heat leakage and all that. Instead, let's just move the water up and down mountains cause keeping mass in one place is easy. Then when we want to take out our energy, we just run the water through some turbines as it flows down.. wah lah, we have an energy storage technique with apparently around 75% efficiency.
In all honesty though, if I'm interpreting you right Its because we already have the infrastructure (dams) in place for other things and no one's going to drop a couple mil on something that might or might not be efficient.

[Anonymous No.10457112]

>>10457094
No, it's a device, that has 10kW internal power needs, and excess power of 5kW , all power is powered by heat from air.

Not storage, production. It creates cold point, which absorbs heat from the air, and uses this energy for something + maintaining the cold point.

[Anonymous No.10457198]

second law of thermodynamics, you will never get positive energy output from this?

[Anonymous No.10457207]

What approach do i use for the particular solution (not English native, the non homogeneous one)?

[math]y'' + 2y' + y = x + 4 e^{-x}[/math]

I've tried [math]y_p = x(Cx+D e^{-x}) = Cx^2 + Dxe^{-x}[/math] (since the homogeneous solution is [math](Ax + B)e^{-x}[/math]) and just ordinary [math]Cx + Dxe^{-x}[/math] but it doesn't work out. I'm always left with no D's left so i can't solve for [math]e^{-x}[/math].

Hilfe, por favor.

[Anonymous No.10457208]

>>10457198
>closed system
By your logic solar power won't work.

[Anonymous No.10457249]

>>10457208
what?
you're acting like this is some sort of perpetual motion device. Its going to take more power to run the pump than you'll produce from your turbine.
If this shit worked for production, why not just shut off the engine after you've started it, and let your turbocharger run a heat engine from that bit of heat. Your car should just run itself.

[Anonymous No.10457459]

would it be a bad time to try to get into any sort of research experience with a professor? semester ends may 5th or so, and i dont know if i could work through summer (unless paid), but i could work in the fall

[Anonymous No.10457479]

>>10457459
if you care about grad school, are vaguely competent and interested in the research, and do not feel the professor is a sadistic sociopath then yes. Otherwise no wait for another opportunity, I am assuming you're a sophomore and not someone with a 3.3 gpa in senior year.

[Anonymous No.10457497]

>>10457479
w-what if im a person with a 3.8 gpa in senior year (graduate in december)?

[Anonymous No.10457621]

>>10457207
Use [eqn]C+Dx+Ex^2 e^{-x}[/eqn]

[Anonymous No.10457711]

>>10457249
COP of heatpump is greater than inverse coefficient of performance of turbine?

Do you realize that common AC is by your standards perpetual motion device, because it's COP is greater than 1?

[Anonymous No.10457714]

>>10457497
If you need some GPA to measure your worth, you're wrothless.

[Anonymous No.10457728]

>learn in high school about fundamental forces, including gravitational force
>advance in the studies
>"lol gravity isn't actually a force", we were just kidding

It's just an example, another would be like how they teach you that there are cones in the eye that are specially sensible to red, green and blue wavelengths and then your learn that's not true or a thousand other cases.
They force you into learning this "simplified", distorted version of the knowledge we have and then as you advance you have to relearn most things because what you learnt wasn't true.

Is this really the most efficient way to teach? Or the most efficient way to learn?

[Anonymous No.10457743]

>>10457714
? the person i replied to included it so i did?

[Anonymous No.10457759]

>>10457743
So you're both equally wrothless now.

[Anonymous No.10457763]

>>10457728
because science is, at the end of the day, just an approximation this is indeed one of the better ways to teach it. you can't jump into learning about gravity in any deep manner without first learning about tensors and lagrangians at the meaningful level so naturally you just use the earlier approximation for it

[Anonymous No.10457764]

>>10457728
It's to maintain the fact you can be marked as delusional if necessary.

[Anonymous No.10457765]

>>10457759
epic

[Anonymous No.10457827]

How do we know the expansion of the universe is accelerating?

I have heard that distant galaxies are moving faster than near ones, and that this means they're accelerating. But isn't this actually what we would expect to see if they were decelerating? Distant galaxies are older than near galaxies. So they were fast in the distant past and are slow now. Sounds like deceleration to me. What am I missing?

Follow-up question: How do we tell the difference between space expanding and things simply moving away?

[Anonymous No.10457848]

OK, my mind is being messed with right now.
We have that for a (commutative with 1) ring [math]A[/math] and a module [math]M[/math] over it, then (trivially) [math]A\otimes_A M\cong M[/math]. But now my book is saying [math]A^n\otimes_A M\cong M^n[/math]. It seems like it should be a canonical isomorphism, but it's not obvious to me that the A^n-orbit of an element will cover all of M^n..

[Anonymous No.10457947]

How do I do QR factorization on non-square matrices? I'm so fucking lost.

[Anonymous No.10457999]

I heard that farms produce a large amount of pollution like water contamination, but how exactly would you solve pollution from a farm without sacrificing the yield? Fertilizers, pesticides, etc. all help and must serve a purpose right?

[Anonymous No.10458263]

>>10457207
> What approach do i use for the particular solution (not English native, the non homogeneous one)?
> [math]y'' + 2y' + y = x + 4 e^{-x}[/math]
Ignoring initial conditions, the Laplace transform gives you
(s^2+2s+1)Y=1/s^2+4/(s+1)
=> (s+1)^2Y=1/s^2+4/(s+1)
So the characteristic polynomial is s^2(s+1)^3. The general form will be a/s+b/s^2+c/(s+1)+d/(s+1)^2+f/(s+1)^3 corresponding to a+bx+ce^-x+dxe^-x+(f/2)x^2e^-x.

Substituting that into the LHS gives you fe^-x+bx+a+2b
=> f=4, b=1,a+2b=0 => a=-2, c=0, d=0
=> y(x) = 2x^2e^-x + x - 2

[Anonymous No.10458299]

>>10457999
The farmers can try to control where their run-off goes. If you can prevent it from getting into nearby rivers and streams, you can solve a lot of the problem.

[Anonymous No.10458333]

Is the University of Tennessee a good place to study physics?

[Anonymous No.10458444]

>>10458333
At UTK right now, in nuke engi not physics, but should be as good as any. We've got tons of labs, and every physics class I've taken has had good professors.

In the end though, you are literally going to get the same shit taught to you no matter where you go.

[Anonymous No.10458642]

glad my social skills are so shit i cant even email someone to ask to join a research lab

[Anonymous No.10458667]

Why do clouds form at their height, instead of say closer to the surface?

[Anonymous No.10458733]

>>10457848
Consider the map [math]A^n \times M \rightarrow M^n \\ ((a_1, a_2, \cdots, a_n) , m)\mapsto (a_1m, a_2m, \cdots, a_nm)[/math].
Check that this is A-bilinear, so that you have the induced linear map [math] A^n \otimes_AM \rightarrow M^n [/math].
Construct the inverse of this map.

[Anonymous No.10458735]

>>10458667
Some times they do form at the surface. What do you think fog is?

[Anonymous No.10458800]

why is this blocking words unlisted?

var expressions_blocked = ['example1', 'example2',
];
function selectionByExpressions() {
var titles_posts = document.querySelectorAll('div.list-l h3>a');
for (i = 0; i < titles_posts.length; i++) {
for (j = 0; j < expressions_blocked.length; j++) {
var hache = titles_posts[i].innerHTML.toLowerCase();
var hache2 = expressions_blocked[j].toLowerCase();
if (hache.indexOf(hache2) > -1) {
titles_posts[i].parentNode.parentNode.style.display = 'none';
}
}
}
}
if (expressions_blocked.length > 0) {
selectionByExpressions();
}
expressions_blocked = undefined;

[Anonymous No.10458805]

>>10458800
btw this is for classic.taringa.net

[Anonymous No.10458813]

>>10458800
is this a java bug? for real i cant make sense, it does NOT block all the list, it just blockes the words included and some without any incleded word.
wtf

[Anonymous No.10458847]

>>10458800
NEVERMIND. i realized it is that it is blocking avery post containing the "words" even if the words are contained inside other word. So if you block "pro" it blocks "problem". How can i solve this makinga an exception of the block if the word is surrounded by letters (qwertyuiopasdfghjklzxcvbnm)?

[Anonymous No.10459028]

what are these graphs called?
http://i.imgur.com/D5Q8Y.png

[Anonymous No.10459037]

>>10459028

radar chart

[Anonymous No.10459324]

what's an ordered set? I really don't get what the definition tells.

[Anonymous No.10459392]

>>10458847
Use regexps rather than indexOf(). Or parse the text into words then check whether they occur within an object (rather than looping over an array of words). Also: /dpt/ on /g/ is probably a better place for basic programming questions.

[Anonymous No.10459419]

>>10459324
It's a set on which an order relation has been defined. It can be defined as an ordered pair (X, <), where X is the set and < is the order relation on X. Some examples are: real numbers with the standard order; subsets of a given set with the inclusion relation being a partial order; and so on.

[Anonymous No.10459466]

>>10459324
Sets don't take order into account, {A,B} = {B,A} which means that anything involving time, or any relation that's not symmetric, can't really be expressed here. We need a way to take order into account, so the definition is just about a way to separate sets so that you can define an order later.
If I tell you 'mix the ingredients and then bake the cake' how are you going to express it as sets ? say, mixing is A, and baking is B. If you write {A,B} its the same as {B,A}, but you can't bake first. Under Kuratowski's definition you make the set {{A},{A,B}} =/= {{B}{B,A}} so now you can say, if we have the first case ({{A},{A,B}}) 'the order that appears on both elements of the set goes first'.
You make them from your starting, unordered, sets. The only requirement is for them not be equal. Try to make a definition yourself.

[Anonymous No.10459467]

>>10457094
>Wah lah
Do you mean voila?

[Anonymous No.10459469]

>>10459466
>the order that appears on both elements of the set goes first

I meant the element that appears on both elements of the set goes first

[Anonymous No.10459599]

Trying to find the center of gravity of the shaded area, am I integrating the right thing?

[Anonymous No.10459625]

Is this a proper parameterization for [math]x^{2}+2y^{2}+3z^{2} = 1[/math]: [math]\hspace{0.5cm} r(u,v) = \left< \cos(u)\sin(v),\frac{1}{\sqrt{2}}\sin(u)\sin(v), \frac{1}{\sqrt{3}}\cos(v)\right>[/math], [math]u\in [0,2\pi], v\in [0,\pi] [/math]

[Anonymous No.10459645]

>>10459392
thanks i appreciate your help but i know no programing, i will take my first lecture tomorrow

[Anonymous No.10459674]

Does anyone know if there is an actual name for this proof: "[math]X \sim Geom(p)[/math], show that [math]P(X>k)=(1-p)^k[/math]"? Would like to google how to prove this, but not sure what to search for.

[Anonymous No.10459676]

Given a set of ranked players (first player is the top/best, last player is the worst), what methods could you use to construct a tournament bracket from this?
The obvious way I thought of doing it was just seed each player one-to-one from the list, but there must be a more intelligent way of doing it.

[Anonymous No.10459697]

>>10459674
Cumulative distribution function of geometric distribution

[Anonymous No.10459762]

>>10459467
no its french

[Anonymous No.10459875]

>>10459676
It depends upon what sort of outcome you want. If you want the early matches to be reasonably predictable, you'd maximise the differential between players at each stage, so the highest-seeded players don't meet until the final rounds. For this, you aim to pair seed x with seed x+2^n where n=0 for the final. So with 16 players and assuming that the higher seed always beats the lower seed, the final is 1-2, the semi finals are 1-3 and 2-4, the quarter finals are 1-5, 3-7, 2-6, and 4-8, and the first round is 1-9, 5-13, 3-11, 7-15, 2-10, 6-14, 4-12 and 8-16.

If you reversed the order, so you paired 1-2, 3-4, 5-6, etc in the first round, 1-3, 5-7, etc in the second, and so on (i.e. pair x against x+2^n where n=0 in the first round), the first round would be unpredictable then later rounds become more predictable as the opponents get farther apart, with a presumed 1-8 in the final.

Or you can mix it up and pair 1-16, 2-15, ..., 7-8, so you have some predictable and some unpredictable. Or you can just draw at random.

[Anonymous No.10459880]

>>10459466
>>10459469
what if it's 3 things?

[Anonymous No.10459980]

Can someone build a satellite in the shape of a ball and give it gravity? If yes why hasn't NASA, the cheeki breeki's, the chicoms, or some other space agency tried it?

[Anonymous No.10460166]

Bunping this thread so more questions can be answered.

[Anonymous No.10460171]

I'm starting uni this autumn and I'm thinking of going for either electrical or mechanical engineering. The issue is, I've slacked on my math classes for the past 8 years. When the time came for grading and tests I would sit and just binge learn the material but I never got an actual understanding of what I was learning. My question is, can I boot camp the shit out of the next 5 months and catch up on all the material, or should I look for other universities more suited for my abilities?

[Anonymous No.10460437]

I want to know what I'm doing wrong, for a given 8 man raid, the boss drops 3 pieces of gear you can roll on, assuming everyone rolls need, what's the probability that I win one piece of gear from 7 trials? I thought it would be pq^2 + 6q^3, where p=3/8, and q=5/8, but my answer is coming out to be greater than 1.

[Anonymous No.10460572]

What calculator can you set the base for logarithm?

[Anonymous No.10460662]

What is a negative sum? Is it just replacing + with -?
I'm trying to figure out information entropy and some examples define it as (Px log2(Px)) + (...) and others (Px log2(Px)) - (...). Both produce different results and I don't know what to believe.

[Anonymous No.10460663]

I've got a dumb question about rational expressions. In this problem, what's stopping me from taking the square root of both sides, and getting x=/=-6?

[Anonymous No.10460681]

>>10460663

[Anonymous No.10460688]

>>10460663
-6 squared is 36

[Anonymous No.10460692]

>>10460663
>what's stopping me from taking the square root of both sides, and getting x=/=-6?
what do you mean x=/=-6?

if you mean x=-6
x^2=-36
(-6)^2 = (-6)*(-6) = 36 which is not equal to -36

[Anonymous No.10460723]

How do I get a strong math background up to calculus, including calculus? I am pretty decent at precalc, but I don't know everything. Also, I'm pretty much a noob at calc. I want to have a strong base at precalc, and use that to get decent at calc.

So what I'm asking for is if anyone knows of some material where you can revise the whole of precalc, without it being a 1000 pages, so I can have a strong base for calc? Also, I just need to know enough calculus to be able to do engineering, so I'm not really looking for a hardcore calc book with infinite theorems and proofs. pls halp

[Anonymous No.10460804]

>>10460723
practice, practice, and more practice.

[Anonymous No.10460811]

>>10460662
> What is a negative sum? Is it just replacing + with -?
It's just the negation of the sum.

> I'm trying to figure out information entropy
All of the P(i) will be <1, so their logarithms will be negative.

> some examples define it as (Px log2(Px)) + (...) and others (Px log2(Px)) - (...). Both produce different results and I don't know what to believe.
You either need to negate *all* of the terms (not ignoring the first term), or negate their sum.
(-a)+(-b)+(-c) = -(a+b+c).

[Anonymous No.10460842]

>>10460572
Most calculators provide base-10 and natural (base-e) logarithms. Some also provide base 2. I haven't seen a binary log(x,base) operation on a conventional infix/postfix calculator, although programmable calculators often provide it as a function (if not, you can just define it). For everything else, log[b](x)=log(x)/log(b) (it doesn't matter which base you use for the RHS).

[Anonymous No.10460860]

>>10460437
The probability you win at least one piece of gear is the same as 1 - Pr( No pieces of gear).

For one loot drop, the probability you do not win one piece of loot is 7/8 (seven other people could win assuming equal chance). Similarly 1/8 is the probability you win that loot.

Since you are rolling off on three different pieces of loot where the probabilities are independent of one another and there is either success or failure, this would be classified as a Bernoulli trial.

So, the probability you at least one piece of gear is,

1 - (3 choose 0) * (1/8)^0 * (7/8)^3 = 33%

[Anonymous No.10461149]

Here's an oddball about poker

Players: 2 - My hand has a 48.15% chance of winning. Of the remainder of the cards, my opponent has the perfectly average hand which 52.85% chance of winning (excluding ties).
Another player joins the table (now 3 players, myself included) with another perfectly average hand (yes I know). What does my chance of winning equate to with the knowledge that I have?

[Anonymous No.10461330]

>>10448476
what sort of useful project could a beginner learn on with basic skills?

[Anonymous No.10461344]

>>10461330
Pick something you are interested in and go with it. If you don't like it, you won't learn it

[Anonymous No.10461469]

>>10446589
Does this series converge or diverge? I'm pretty sure it diverges but I'm not sure.

[Anonymous No.10461476]

>>10461469
This clearly diverges

[Anonymous No.10461485]

>>10461476
danke
I wasn't sure if the negative sign affected it.

[Anonymous No.10461537]

I've been eating my cum after jacking off for 3 days now and about 36 hours ago I developed a large and painful canker sore on the inside of my cheek. Could this skeeteating be the cause?
Also, between.the ages of about 14-16 I would always eat my cum and I never developed canker sores, this is the first I've ever had actually.
pls help

[Anonymous No.10461544]

>>10461537
I should also note that Ive jacked off about 8 times in the last 3 days

[Anonymous No.10461593]

>>10459980
please answer mah question FOR I MUST BE OF KNOWINGS!

[Anonymous No.10461930]

My algebra skills are shit.
Any tips on getting from the first line to the second?
Or any online calculators or matlab programs I can use?

[Anonymous No.10461946]

>>10461930
nvm i got it

[Anonymous No.10462269]

How would you go about processing this by hand?

[Anonymous No.10462276]

>>10462269
just draw the graphs and kind of guess

[Anonymous No.10462295]

>>10462276
Gotta be a more precise way.

[Anonymous No.10462328]

>>10462295
newton's method?
https://math.stackexchange.com/questions/638563/finding-intersection-with-newtons-method-for-cosx-2x

[Anonymous No.10462772]

>>10462269
x=0 is one solution. For the other: Newton's method gives 0.3274097742770376.

[Anonymous No.10462841]

Alright bros. I have made it all the way to polar coordinate double integrals in calc 3 without learning the unit circle and it seems like I'm going to have to remember it now. What's the best way to grind it?

[Anonymous No.10463266]

>>10462841
remember one quadrant and use common sense to figure out the others

[Anonymous No.10463542]

Are transmission lines important in signal processing?

[Anonymous No.10463827]

Can someone post the meme similar to the expanding brain meme where the first panel is Pythagoras' theorem and then the Cauchy Schwarz inequality and then det(A^t A) >= 0

[Anonymous No.10463948]

I have to solve a lot of random hard integrals. Is there an easy way to recognize which one is easily solvable via complex analysis instead of just brute forcing it Calc II style?

[Anonymous No.10463979]

Is there a collective name for operators (or the operations themselves) on sequences like the capital sigma for summation or the capital pi for a product of a sequence?

[Anonymous No.10464031]

>>10463979
Functionals

[Anonymous No.10464075]

need a quick reminder on how to do surface integrals with vector functions and pauls notes are too uhh useless

[Anonymous No.10464084]

Could any asshole with Crispr, some chickens, and a lot of free time reverse engineer a Dinosaur?

[Anonymous No.10464263]

>>10459599
Please
Please
Please respond

[Anonymous No.10464277]

>>10461537
>>10461544
pls respond

[Anonymous No.10464289]

What's wrong the the obelus sign? Why have we abandoned perfectly good notation?

[Anonymous No.10464299]

>>10464289
discontinuous/must lift pencil twice to complete
too strenuous for those who can't build muscle, I'd rather just draw a plain bar

[Anonymous No.10464338]

>>10464084
Define "a lot". We don't have nearly enough understanding of the actual interactions of the extremely complex systems that make up organisms. Beyond trivial changes we don't really have any way of predicting what a change to a genome will do except to make the change, grow the chickens, and see what happens. And our understanding of dinosaur genomics is minimal.

So I suppose with a huge budget and millions of chickens (each with a single CRISPR-induced mutation) to screen over many generations one could eventually sculpt, one trait at a time, something that would look and behave somewhat like what we think dinosaurs looked and behaved (though it would differ from a real dinosaur genetically).

Basically CRISPR gives you the ability to modify any part of a machine. You have one extremely complex machine whose behaviour you can observe, and in which you understand what a very small number of parts does, and another machine, about whose internal workings you know next to nothing, but you think you know how it behaved. Your goal is to build a replica of the second machine by modifying the first machine. Once you understand enough of the workings of the first machine you may be able to build something similar to the second machine around it, though it's not likely it will internally resemble the original second machine.

[Anonymous No.10464367]

>>10464338
>Basically CRISPR gives you the ability to modify any part of a machine

Note that, for the most part, this means "selectively break a part" and see what happens.

[Anonymous No.10464369]

How do I read this?
My grade was 84, so that's what that box is.
Trying to determine how many people scored high and low, below the average, etc.

[Anonymous No.10464388]

>>10464369
It's a box plot showing interquartile range

[Anonymous No.10464450]

>>10464388
Can you explain it to me in dummy terms? I haven't taken stats since highschool

[Anonymous No.10464588]

>>10464369
do you go to mercer?

[Anonymous No.10464601]

We're doing parametric functions in Calc II right now.

We're supposed to eliminate the parameter of
x=sin(.5θ), y=cos(.5θ)
apparently you're supposed to use sin^2θ+cos^2θ=1 but I'm just not making the connection

how do I eliminate that parameter using that identity?

[Anonymous No.10464611]

>>10464601
let t=.5*theta
rewrite your equations with t instead and it should become even more clear
if you're thinking "there's no way it's simply...", you're wrong, it is supposed to be simple

[Anonymous No.10464648]

>>10464338
There's scientific papers describing scientists that accidentally and purposefully have identified genes that when altered affect snout, tail, and leg growth. But I understand that it's kinda a crapshoot as to whether the thing even comes out kicking.

[Anonymous No.10464694]

>>10446589
Why is this not a circle? or more importantly: What is it?
x and y are just a summation of 1 to n and then -1 to -n. No I don't know how to put that in mathspeak.
What did I just draw and why is it so deceptively close to a circle?

[Anonymous No.10464747]

What causes us to feel a "metallic taste" when licking metals? We are supposed to have receptors for saltiness, acids, etc not metals right?

[Anonymous No.10464766]

>>10464694
what in gods name are you doing

[Anonymous No.10464770]

>>10464648
That's the screening I mentioned. The problem is the systems are too complex to be predicted outside of very simple and/or well studied scenarios, and there are few useful abstractions inherent in the 'design' that we have managed to characterize which would let us reason about how things operate. So just look at the tens of thousands of parts that are there, break one at a time, and see what happens.

If breaking a part makes the animal's snout bigger, you know there's some association between that part and the way the snout is generated, but the actual dynamics of that association merit separate investigation. Most likely you broke some regulatory pathway that affects snout growth (and likely many other things).

[Anonymous No.10464786]

>>10464766
I was playing Megaman Zero and I saw 2 of these bombs that either move up and down or left and right. And I thought "that would make a circle if I graphed it out". Then I did but disappointingly it's not quite a circle.

[Anonymous No.10464807]

Can someone help? >>10461149 I've been stuck for three fucking days

[Anonymous No.10464893]

Why does tan(arctan 4) come out to 4 instead of "not defined" while cos(arccos 1.2) is considered "not defined"?

For that matter, why does arcsin[sin(9pi/8)] come out to -pi/8 instead of "not defined"? I thought all this shit was way out of bounds.

[Anonymous No.10464914]

>>10464747
'Metallic' smell and taste is actually the smell and taste of human is actually the smell and taste of organic compounds (e.g. lipid peroxides) of your body reacting in the presence of metal ions and producing odorous compounds.

Coins have a metallic smell because they've been touched by people and what you're smelling is essentially the remains of their sweat after reacting with metal ions. A fully clean/freshly minted coin doesn't have the smell.

[Anonymous No.10464929]

>>10464893
arctan is defined for all real numbers so 4 is valid.
arccos for -1 to 1 so 1.2 is invalid
anything defined for sin will be defined for arcsin so arcsin[sin(9pi/8)] is valid.
sin(9pi/8) is valid because sine is periodic (repeating)
arccos and arcsin are not periodic

[Anonymous No.10464932]

>>10464929
>anything defined for sin will be defined for arcsin so arcsin
resulting from sin* not "defined for sin"

[Anonymous No.10464935]

>>10464914
Interesting. So the ionic nature of metals strips parts of organic matter from organisms it touches and that is what you can feel.

[Anonymous No.10464996]

>>10464935
"Strips" is a big word; we're talking about compounds dissolved in sweat/saliva here. You'd leave some of them on anything you touch/lick, it's just that they happen to react in the presence of metal ions.

[Anonymous No.10464999]

>>10464694
> Why is this not a circle? or more importantly: What is it?
A quadratic curve, aka parabola.
> x and y are just a summation of 1 to n and then -1 to -n.
The sum of 1..n is n(n+1)/2 = (1/2)n^2+(1/2)n

> What did I just draw and why is it so deceptively close to a circle?
See "Beziér Curve" and "Finite difference" for a formal treatment.

For a perfect circle, use a rational curve:
x(t)=(1-√2)*t^2-(2-√2)*t+1
y(t)=(1-√2)*t^2+√2*t
w(t)=(2-√2)*t^2-(2-√2)*t+1
then x'=x/w, y'=y/w.

This corresponds to a rational quadratic Beziér curve with control points [1,0,1], [1/√2,1/√2,1/√2], [0,1,1].

A quadratic polynomial f(x)=ax^2+bx+c can be evaluated at fixed steps f(n*d) via:
f(0)=c
g(0)=(a*d+b)*d
f(x+d)=f(x)+g(x)
g(x+d)=g(x)+2*a*d^2

[Anonymous No.10465090]

when in math studies (in what class) does hilbert and banach space get taught initially?

[Anonymous No.10465125]

>>10464999
Oh yeah I guess I just stuck 4 parabolas together.
Thanks anon. The rational curve definitely works
Circles are more complex than they seem

[Anonymous No.10465232]

Do thorium fission reactors need to be bigger than uranium ones? Could we have thorium nuclear submarines and aircraft carriers without changing the measures too much?

[Anonymous No.10465343]

Ok, 4channel. Up until this point i followed every single meme and advice you have given me, I dont see why I should stop now !
Im doing BA CS in a pretty good University.
Its time for me to pick my major, I have a choice between :
-Cybersecurity
-Data Science
-Software Design/Development
(and some other meme majors that I dont even want to mention)
Im personally leaning more towards Data Science since I heard thats where the money is, and it seems like a brainlet filter.

[Anonymous No.10465355]

>wikipedia claim supported by four citations
>three of those just cite the fourth one

why is this allowed?

[Anonymous No.10465365]

>>10465090
Most likely, real analysis. Although Hilbert spaces could show up in other applied math type courses where they avoid lengthy discussions about Banach spaces.

[Anonymous No.10465367]

>>10457040
>How do I prove using chi-square test that this variable has exponential distribution?

You can't. And you still can't even in the discrete case. the only valid use of this test is to show that the distribution *differs* significantly from the null (i.e chi-square) distribution. Using the test in the way you propose is circular reasoning, because deriving the distribution of the test statistic requires assuming the null hypothesis to be true, which is what you are trying to show in the first place.

[Anonymous No.10465368]

I'm finding the definite integral of :
18x^3 - 18x - 1 dX
------------------
X^3 - x^2

using partial fractions and systems of linear equations.

I got A/x + B/x^2 + C/(x-1) as my

So
18x^3 - 18x - 1 = A/x + B/x^2 + C/(x-1)

Setting it up as a system of linear equations I get
0 = x^3(A+C)
18x^2 = x^2(-A+B)
-18x=(-B)

But what happens to the -1? Am I misunderstanding something?

[Anonymous No.10465432]

>>10465368
You should do long division first.

Also, to get the system of equations, you should multiply your equation by the 'least common denominator' so that there are no more fractions left. In your case, that would be 'x^2(x-1)'. Then try to find the system of equations.

[Anonymous No.10465457]

>>10465368
The numerator and denominator have equal degree, so you need to perform polynomial division first (if the numerator has lower degree than the denominator, this yields a quotient of zero with the original expression as the remainder, so you can skip this step in that case).

18x^3 - 18x - 1 = 18*(x^3 - x^2) + 18*x^2-18*x-1
=> (18x^3 - 18x - 1)/(x^3 - x^2) = 18 + (18*x^2-18*x-1)/(x^3 - x^2)
= 19/x + 1/x^2 - 1/(x-1) + 18

[Anonymous No.10465474]

>>10465343
Switch to gender science.

[Anonymous No.10465546]

>>10465432
I thought long division was used when the degree of the numerator was greater than the denominators
>>10465457
My apologies the numerator is
18x^2 - 18x - 1 dX
not 18x^3 - 18x - 1 dX

[Anonymous No.10465720]

Is [math](-\infty, \infty) \rightarrow \mathbb R^+[/math] the same as [math](0, \infty) \rightarrow \mathbb R^+[/math] or am I misunderstanding the basic syntax?

[Anonymous No.10465731]

>>10465720
No, they are not the same, what do you understand by each of those expressions?

[Anonymous No.10465751]

>>10465731
I figured it was an interval over the set of positive reals, and because of that the negative part doesn't do anything. Does it instead mean that "this function takes values in the range [math](-\infty, \infty)[/math] and the result is in the set of positive reals," or something else?

[Anonymous No.10465763]

>>10465751
>Does it instead mean that "this function takes values in the range [math](-\infty, \infty)[/math] and the result is in the set of positive reals,"
Yes, you are describing functions, and they aren't the same because of different domains. What you were trying to describe is basically just an intersection, from what I understand.

[Anonymous No.10466215]

whats the fastest way to learn a language? arabic to be precise?

[Anonymous No.10466331]

>>10466215
be arab

[Anonymous No.10466336]

>>10466215
Isis

[Anonymous No.10466449]

Brainlet here. Does magnetic force or gravity have a "speed"? I mean, if you attach a magnet to an iron bar it will magnetize, if i had, let's say, a trillion km iron bar and attach the magnet at one end, will the other end magnetize istantly?
Same for gravity: is the effect istantaneous or there's a delay like with light (seeing the light of a dead star thing)?

[Anonymous No.10466590]

for a set {2,3,4,6,8,9,12,18}, I'm supposed to apply the divides relation and draw the hasse diagram, but 3 doesn't divide by 2, so how am I supposed to start this?

[Anonymous No.10466784]

I found what I wanted. A practical guide on how to read and make diagrams, documented software and so on.

You guys have no idea the relief I feel after literal days of going through a rabbit-hole and huge demoralization because I kept bumping into retarded useless books

http://gen.lib.rus.ec/book/index.php?md5=4C9486D7D9238AF5B49A0D4C60B38895

I can finally rest

[Anonymous No.10466810]

y my pp stiff

[Anonymous No.10466896]

What would I look up to study/practice for "fractional perfect squares"?
I mean things of the form 16t^2-4+(1/(4t^2))

[Anonymous No.10466988]

What upper division math course should i take if I’m interested in Signal Processing?
Functions of a complex variable?

[Anonymous No.10467540]

Are combustion and explosion types of oxydations? Or are they separate things? Are explosions a type of combustion?

[Anonymous No.10467601]

>>10465232
Yes, because you need an emergency cooling pool below the salt plug. You also need all the facilities to deal with fluorine.

[Anonymous No.10467610]

>>10467540
Explosions aren't one single thing. Any time you have a sharp gradient between high and low pressure zones, you have an explosion.

Combustion is a type of oxidation, and explosions are often, but not always, caused by oxidation. Popping a balloon is an explosion.

[Anonymous No.10467635]

>>10467610
Thanks a lot.

[Anonymous No.10467698]

Can someone help me out here? I'm doing this seminar where I have to solve like 30 problems, but many of them have wrong results, so I have no idea if I actually solved it or not.

I have to calculate the smallest speed the bowl can rotate without the object resting on its wall falling down.

friction coefficient is 0.05, ß is 15°, and radius is 0.5m.

It's supposed to be a fairly simple problem, but I keep getting different result from the professor.

The given result is 74,5 rpm. I keep getting 181.4 rpm, even after multiple tries.

Will post another pic showing I actually tried to solve this shit, so you niggas don't think I'm asking you to solve my homework.

[Anonymous No.10467707]

>>10467698

[Anonymous No.10467711]

>>10467707
Supposed to get

[Anonymous No.10467757]

>>10467707
Imagine being this fucking stupid.

[Anonymous No.10467760]

>>10467698
http://www.batesville.k12.in.us/physics/phynet/mechanics/circular%20motion/banked_with_friction.htm

[Anonymous No.10467781]

>>10467760
I've had a banked car problem and solved it correctly... not sure what I'm fucking up in this example?

[Anonymous No.10467786]

how do i prove [math](A + B)^T = A^T + B^T[/math] ?

[Anonymous No.10467813]

>>10467786
From the definitions of + and ^T

[Anonymous No.10467819]

>>10467813
sorry i suck at proofs, can you please spell it out for me?
this isnt for hw, just self study. my book proves (AB)^T = B^T A^T but omits discussing/proving linearity for transposition

[Anonymous No.10467836]

>>10467786
By not being retarded. Verbally, if you add them together and move the elements of the matrix, you can decompose the sums back into two matrices that are the same as the transposing the original terms.

A simple example,
A = [a b; c d] B = [e f; g h].
[a b; c d] + [e f; g h] = [a+e b+f; c+g d+h]. Transpose to get [a+e c+g; b+f d+h] and then realize that this is equal to [a c; b d] + [e g; f h], which is the same as A' + B'.

It should intuitively follow that this procedure will be identical for matrices of arbitrary dimensions.

[Anonymous No.10467840]

>>10467836
maybe i should read How to Prove It
i can read a proof and follow along and even memorize them and they make total sense
but when i sit down to do it myself my mind is just blank

[Anonymous No.10467860]

>>10467840
What motivates you to sit down and do it?

[Anonymous No.10467864]

>>10467860
just trying to firm up my base of understanding and it feels like something i should be able to do

[Anonymous No.10467884]

are there any animals that suck dick or is that human only?

[Anonymous No.10467890]

>>10467864
Being able to do something and actually having a reason to do it are two different things. If you don't know what you're doing, you won't know how to do it. Your desire to understand comes from somewhere, and there you will find your deepest creativity.

[Anonymous No.10467899]

>>10467890
any advice for developing my proof abilities, other than simply spending more time at it?

[Anonymous No.10467906]

>>10467884
dolphins, bats, bonobos to name a few

[Anonymous No.10467907]

Is this equation right? I tried to work it out but the units don't end up being electron volts or joules and the answer works is something I know is not the ground state of hydrogen.

[Anonymous No.10467913]

>>10467899
Know why you want to do it.

[Anonymous No.10467915]

>>10467913
i already know the answer to that.

[Anonymous No.10467924]

>>10467840
Just do what I did for the sum of two nxm matrices instead of a 2x2. You'll have to have some ...'s in there, but it should be doable. A transpose operation just takes a_ij and puts it in a new matrix in the position ji, but you must understand that being distributive isn't exclusive to the transpose operation. If I flipped the matrix vertically (placing a_ij in position (i_max-i)j, this would also be true. Any index swapping operation that only depends on the dimensions of the matrix will be distributive.

If you want to intuitively get it, take two pieces of transparency and partition them into a grid that has nxm cells each. Use dots to represent the value in that cell. 1 dot = 1, 2 dots = 2, so on. Now, perform a transpose on each sheet individually. Do this by flipping it about the diagonal running from the top left to the bottom right of the sheet. Now add them by putting the sheets on top of one another, what do you see? Now, put the sheets on top of one another from the beginning and transpose them, what do you see? Why does this happen? If you understand this, the proof is identical except you have variables instead of dots, and flipping the sheet is replaced by mapping the indices of one matrix to another.

[Anonymous No.10467939]

How do I approach a simple harmonic oscillating system where the spring's mass is non-negligible? Specifically, how would I go about finding the kinetic energy of the spring?

[Anonymous No.10467942]

>>10467915
Self-knowledge is primal. I'm not talking about whatever answer you shoot off to anyone querying why you do what you do, I'm saying the answer you have for yourself. The motivation you're aware of. When you know that, you can control your focus toward that end. If you find that you can't control your focus like you expected to be able to, then you need to rethink why you're doing this. A lot of the time we end up putting ourselves in situations we never wanted to be in because other people wanted something, and we didn't have the fortitude to say, "No." Knowing what you want for yourself isn't easy, and might not come all that naturally.

[Anonymous No.10467949]

>>10467939
It may be obvious but I'll clarify that this is a mass-on-spring problem with one fixed end.

[Anonymous No.10467951]

>>10467939
kinetic energy of any rigid non rotating system is always 1/2 mv^2

[Anonymous No.10467962]

>>10467907
Never mind, found out e stands for the elementary charge, I thought it was the constant e lol.

[Anonymous No.10468045]

>>10467939
Replace (1/2)*m*v^2 with integral (1/2)*v^2 rho dx over the length of the spring (where rho is mass/length). v varies linearly from 0 at the fixed end to the velocity of the mass at the other end.

Similarly, the potential energy of the spring will be an integral along its length.

Model the non-light spring as a chain of spring-mass-spring-mass-... then convert the summation to an integral.

[Anonymous No.10468056]

>>10467951
I think that may understate the problem a bit. The linear density of the spring will change with time and the velocity of the spring is not a constant (boundary conditions tells you that v(0,t) for the spring is 0. You would expect something that oscillates, and the amplitude can be reasoned from an energy balance, but the rate at which it oscillates certainly depends on the mass of any weight and the mass of the spring, and I suspect that it may not be perfectly sinusoidal.

The system will be exchanging KE with PE in the process of oscillating. Intuitively, you know that because the potential is harmonic, your extrema x where KE = 0 and PE is maximized will be dependent on how much energy was present at the beginning. KE_max = PE_max = PE_0 + KE_0. KE_min = PE_min = 0. You can also reason that x_max should be 2(KE_0 + PE_0)/k due to conservation of energy.

I don't know what the dynamics will be, but I would suspect that it ends up being a nasty PDE that requires some additional tricks to solve or may even require a numerical solution. I can say that rho(t) should be pretty easy to work out by considering the exact geometric construction of the system. v(t) need to come from a differential equation, my initial thought is to solve the simple oscillator problem for the KE(t) of an infinitesimal slice dx (with mass rho(x)*dx) and integrate across x to get the time dependence of the total KE of the system.

[Anonymous No.10468064]

>>10468056
perhaps this is what you're looking for?
https://en.wikipedia.org/wiki/Effective_mass_(spring%E2%80%93mass_system)#General_case

[Anonymous No.10468080]

>>10468064
non-dimensionalizing op

[Anonymous No.10469206]

>>10446589
How do I into learning linear algebra in 3 days?
What resources would you recomend?

[Anonymous No.10469540]

why does repeating "folding" on 2 lines like in pic related infinetly not produce a diagonal line?
if the width and height are 1, the length of infinite folded is 2 while the diagonal is root 2

[Anonymous No.10469556]

>>10469540

[Anonymous No.10469681]

>>10447737
Sorry in advance; I don't post on this board often, so I don't know the notation to create math equations very well.
I think it's normal fraction multiplication/simplification, like:
[math]\frac{a}{b}\cdot/frac{c}{a}=\frac{c}{b}[/math]

[Anonymous No.10469686]

>>10469681
Shit. Correction attempt:
[math]\frac{a}{b} \cdot \frac{c}{a} = \frac{c}{b}[/math]

[Anonymous No.10469706]

>>10469540
Disclaimer: Take what I say with a grain of salt.
I believe that since you start with 2 lines each of length 1, and you are only moving line segments around that maintains the total lengh of all line segments, the total length of 2 is preserved. So even as the length of each individual line segment approahes infinity, the "net length" remains constant. So, even though the length between both endpoints is root 2, at an infinitely small scale there are those zigzag patterns that make it 2 lines packed very close together, instead of an actual straight line.
Someone please correct me if I am mistaken.

[Anonymous No.10471367]

You have a cake shaped as a circle. You cut it into thirds. What happened to that .0000000001?

[Anonymous No.10471512]

>>10463827
Bump. Please help me

[Anonymous No.10471565]

I'm an undergrad with long hair. I'm looking into finding a research lab to get into. Do professors care if a guy has long hair (Biochemistry)? Would I be better off cutting it?

[Anonymous No.10471995]

i'm looking to understand the relationship between singular value decomposition and eigenvectors... i know that this is one such way of demonstrating the relationship. can someone elaborate on other ways to understand it?

[Anonymous No.10472004]

>>10471995
Also, what fundamentally makes a matrix diagonalizable? I know that you can only diagonalize a matrix that has linearly independent eigenvectors but is there a matrix with linearly independent columns that *doesnt* have linearly independent eigenvectors and therefore which isn't diagonalizable? And if so, what makes it not have linearly independent eigenvectors?

sorry if brainlet questions...

[Anonymous No.10472137]

>>10472004
> is there a matrix with linearly independent columns that *doesnt* have linearly independent eigenvectors and therefore which isn't diagonalizable?
Shear matrices (i.e. an identity matrix with one non-diagonal element changed to a non-zero value) have a single repeated eigenvalue and single repeated eigenvector. Rotation matrices only have one real eigenvalue and so aren't diagonalisable over the reals.

[Anonymous No.10472161]

If I want to get smarter, should I stop posting questions here and just go to my professor’s office hours?

[Anonymous No.10472165]

hi /sci/ i have my analysis 1 exam in about a month. i understand the definitions and theorms better every day and it is coming together better in my mind. but i cannot wrap my head around proofs. i can follow some of them but proofing something on my own is nearly impossible. what do? help very appreciated.

[Anonymous No.10472174]

>>10466988
Bump

[Anonymous No.10472537]

I'm a big fucking dumbass, and I swear this isn't homework. This applies to a problem in my actual life.

There's three segments connected by hinges spanning a gap. A weight rests on the middle segment. How do I calculate the force on the hinges? When I look up moment arms and shit there's always just one point of rotation.

[Anonymous No.10472543]

>>10472537

Like, can I pretend that the middle segment is fixed, and half the force of W is being applied to each segment where they contact the edge of the gap?

[Anonymous No.10472569]

>>10472537
>>10472543

[Anonymous No.10472648]

>>10472537
Initially, you can assume symmetry (presumably it's meant to be symmetric). But that's unstable. As soon as it starts to become asymmetric, the resultant forces will tend to make it more asymmetric.

The contact forces depend upon the mass and moment of inertia of each of the segments. If they were light, the whole thing would fold up instantly and W will just fall under gravity.

As for solving it: the linear velocity of a hinge can be calculated as v[h]=v+r*ω where v is the linear velocity of some fixed point P within the segment, ω is the segment's angular velocity, and r is the distance between P and the hinge's axis. Applying that calculation to the segments on both sides yields the same result, so you have v1+r1*ω1=v2+r2*ω2. Differentiating changes linear and angular velocities to accelerations.

[Anonymous No.10473054]

I am stuck on (d) how does one solve this?