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/sci/ - Science & Math

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9263958 No.9263958 [Reply] [Original] [archived.moe]

the other thread >>9256335 is pretty much dead

in the definition of an ideal I of a ring R is there any difference in requiring that I is a subgroup of R under addition and requiring that I is a subring of R?

>> No.9263974

yes beacuse not all additive subgroups are subrings

by the subring test a subset is a subring if it is closed under multiplication, subtraction and contains the multiplicative identity


consider the ring Z and the subset 2Z which is closed under multiplication and subtraction but doesn't contain the mult. identity 1

>> No.9263978

How is the big crunch not the correct conclusion for the end of universe?

>> No.9264006

I'm just not understanding feynman's method of integrating bounded integrals of two functions. In the explanation, they appear to use a kernel, something of a 'b' thrown into an integral to equate it to a partial derivative within the integral. I just don't get how you choose WHERE to throw the 'b' in.
A very popular example is the integration of
\int_{0}^{\pi} [math]e^{$\cos{x}$}*{$\cos{$\sin{x}$}$}*dx[/math] into \int_{0}^{\pi} [math]e^{b*$\cos{x}$}*{$\cos{b*$\sin{x}$}$}*dx[/math]

>> No.9264010

also, not very good with LaTeX
[math]\int_{0}^{\pi} [math]e^{\cos{x}}*{\cos{\sin{x}}}*dx[/math][/math] into \int_{0}^{\pi} [math]e^{\cos{x}}*{\cos{\sin{x}}}*dx[/math][/math]

>> No.9264088

Where can I find people that will help me with my homework without making fun of me or telling me to fuck off?

>> No.9264097

I'm sure someone will do that in exchange for money

>> No.9264158

wtf? do you mean [eqn]
\int_0^\pi e^{\cos x}\cdot\cos\sin x\,dx[/eqn]
into [eqn]
\int_0^\pi e^{b\cos x}\cdot\cos (b\sin x)\,dx[/eqn]?
I can't answer the question, but please read the sticky and learn the formatting
basics so someone who might can understand it: start with a [ math] or [ eqn] tag and end with a [ /math] or [ eqn] tag, respectively (without the spaces obviously), don't use dollar $igns, place parentheses around non-trivial function arguments and use \cdot for a multiplication dot

>> No.9264161

How do I construct the green's function from this form?

[math]\mathcal{L}\{G(t,\tau;\vec{x},\vec{\xi})\} = \delta(t-\tau,\vec{x}-\vec{\xi})[/math]

Say for example L is the heat equation's operator

>> No.9264166

[math] \mathcal{L}\{G(t,\tau;\vec{x},\vec{\xi})\} = \delta(t-\tau,\vec{x}-\vec{\xi}) [/math]

>> No.9264189

>in the definition of an ideal I of a ring R is there any difference in requiring that I is a subgroup of R under addition and requiring that I is a subring of R?
Yes, An ideal is a subring with the additional property that any element OUTSIDE of the ideal multiplied by any element of the ideal is INSIDE the ideal.
That property is there so that the quotient can be made into a ring by defining this multiplication (a+I)(b+I):=ab+I.
For it to be well defined, it has to be independent of the representatives, and for this to happen you need the additional property.

>> No.9264190

fuck off

>> No.9264200
File: 20 KB, 631x261, aa7.png [View same] [iqdb] [saucenao] [google]

so the definitions in pic related arent equivalent?

>> No.9264255

The second definition is a bad one.

>> No.9264306

They are equivalent.
The first one at (ii) acounts that multiplication in I is closed (thus subring), and that for x outside I and y in I you have xy in I and yx in I (ideal subring).

The second one is a retarded definition. It's correct, but redundant.
Change textbook. This one seems bad.

>> No.9264310

>They are equivalent.
They're not. Since I is a subring in the second definition, it contains 1, and so R itself would be the only ideal because of (I2).

>> No.9264316

Did 0! = 1 first come from definition or from the Gamma Function? I'm assuming the former but heard someone imply it was the latter. Curious.

>> No.9264329

>The first one at (ii) acounts that multiplication in I is closed (thus subring)

>> No.9264355
File: 1.25 MB, 857x2352, hags_theorem.png [View same] [iqdb] [saucenao] [google]

First let us look at the symmetries of [math]\mathcal{L}[/math]. Suppose [math]T_\vec{a}[/math] and [math]T_\beta[/math] are representations of the space and time translation operators such that [math](T_\vec{a}f)(\vec{x},t) = f(\vec{x} - \vec{a},t)[/math] and [math](T_\beta f)(\vec{x},t) = f(\vec{x},t-\beta)[/math]. If [math][T_\vec{a},\mathcal{L}] = [T_\beta,\mathcal{L}] = 0[/math] then it follows that [math]G[/math] is also translationally invariant, and therefore [math]G(\vec{x},\vec{\xi},t,\tau) = G(\vec{x}-\vec{\xi},t-\tau)
[/math]. So you can WLOG solve the PDE [math]\mathcal{L}G(\vec{x},t) = \delta(\vec{x},t)[/math] to get the Green function, namely the Green function at the origin and [math]\tau=0[/math] determines the full Green function.
If the above is satisfied then you can perform a Fourier transformation. Given [math]G \in \mathcal{S}(\mathbb{R}^n)[/math] is a Riemann square-integrable distribution in space (i.e. [math]G\rightarrow 0[/math] as [math]\vec{x} \rightarrow \pm \infty[/math]), you can Fourier transform in the [math]\vec{x}[/math] coordinates and obtain an ODE in [math]t[/math] which you can solve depending on initial conditions, then inverse Fourier transform back into real space. If [math]G\in \mathcal{S}(\mathbb{M})[/math] is a square-integrable distribution in both the space and time coordinates then you can let [math]x = (t,\vec{x})[/math] and Fourier transform in [math]x[/math]. This gives you an algebraic equation that you can just inverse Fourier transform back directly.

>> No.9264371

Subrings don't necessarily have a unit. A ring might not necessarily have a unit. And even if the ring and the subring have units, they might not even be equal.

Are you retarded or what? I is a subset of R.

>> No.9264373

I meant "unity", not "unit".

>> No.9264375

>Are you retarded or what? I is a subset of R.
Not enough to guarantee being a subring.

>> No.9264376

>Subrings don't necessarily have a unit.
They do for any useful applications.

>> No.9264380

>A ring might not necessarily have a unit

Those are called rngs.

>> No.9264388

1) It is a subset of R.
2) It is a subgroup from the hypothesis.
2) Multiplication can be restricted there since I is closed under it.
3) Associative and distributive laws for * trivially follow since + and * on S are the same ones as on R, just restricted to S.

>> No.9264390

>if the ring and the subring have units, they might not even be equal.
Also wrong.

>> No.9264391
File: 70 KB, 645x729, 1508888817247.png [View same] [iqdb] [saucenao] [google]

>They do for any useful applications.

>> No.9264394

>1) It is a subset of R.
>2) It is a subgroup from the hypothesis.
>2) Multiplication can be restricted there since I is closed under it.
>3) Associative and distributive laws for * trivially follow since + and * on S are the same ones as on R, just restricted to S.
Still not a subring, existence of a multiplicative identity is not implied by any of these statements.


>> No.9264404

[math] \mathbb{Z} \times \mathbb{Z} [/math] has unity [math] (1,1) [/math] .
[math] \mathbb{Z} \times \{0\} \unlhd \mathbb{Z} \times \mathbb{Z} [/math] has unity [math] (1,0) [/math] .

>> No.9264408
File: 56 KB, 645x773, 1496829712394.jpg [View same] [iqdb] [saucenao] [google]


>> No.9264409

>everything turns out to be right
you're just a retard

>> No.9264413


Not a subring, doesn't contain the ring's multiplicative identity.

>> No.9264417

>you're just a retard
Nothing I claimed was wrong has turned out to be right.


>> No.9264421

>hurr I'm right even when I'm wrong


>> No.9264422

Your personal blog is not a legitimate source.


>> No.9264424

Unless you finally point out something I claimed incorrectly (which you can't), there is no "next".

>> No.9264426

I bet you are the same retard who spams Wildberger memes.

>> No.9264430

>I bet you are the same retard who spams Wildberger memes.
You lost that bet.

Plus that doesn't even make any sense, you're the one using unconventional naming and just generally being confused about mathematical standards.

>> No.9264454

>unconventional naming
It's not unconventional at all. It's what most texts use.
If you define a ring to have unity, then you'd get shit like "the kernel of a homomorphism is not necessarily a subring" which is plain fucking retarded.
It's just bad terminology. There is no reason to restrict the definition.

>> No.9264457

>It's not unconventional at all.

>It's what most texts use.

>[blah blah] which is plain fucking retarded.
How so?

>> No.9264458
File: 14 KB, 200x226, e09.png [View same] [iqdb] [saucenao] [google]

whatever you say, friend

>> No.9264462

Feel free to attempt to lend credence to any of your inane statements.

>> No.9264465

>lend credence
You seem very smart, since you are using such words.
I concede.

>> No.9264467

>You seem very smart
I'm not, just smarter than you.

>> No.9264469


>> No.9264478

Meh, there are some relatively natural examples of rings that don't have units (for example L^1 with convolution)

>> No.9264484

>natural examples of rings that don't have units (for example L^1 with convolution)
That isn't a ring, it's a rng.

>> No.9264503

Can someone tell me why this regular expression is failing to accept?

regex: [0-9]{5}
input: 12345

>> No.9264593

Has no one ever heard of tutoring before? Or is /sci/ too socially retarded that the aspect of getting help in person deters them?

>> No.9264616

The latter, and that you usually have to pay for tutors.

>> No.9264665

Why does gas cause feelings of depression and anxiety? It's a pretty immediate effect in most people but I can't find out why.

>> No.9264703

Thanks anon.

>> No.9264722

Because it looks like space itself is expanding at a rate so fast that the effects of gravity will be to weak and slow to pull all the mass back together. It's looking like a big rip or heat death.

>> No.9264723

Not exactly a science question but more of a person question.

How do I find purpose in life when I'm an atheist?

>> No.9264724

Your uni probably has tutors and shit yo.

>> No.9264730

As a fellow athiest I ran into this as well. Your purpose is whatever you want it to be. You just need to focus on doing whatever you focus on well, and being happy.

>> No.9264775

What if I focused on becoming a serial killer and started murdering people at random and did it because I wanted to? People like you make atheists look retarded. Really smart right there.

>> No.9264815

>make atheists look retarded
It's not hard.

>> No.9264825

Pic is shopped?

>> No.9264829

>Taking something to the most extreme, unlikely conclusion because you didn't like my answer
Ok buddy. Just be sad and depressed then.
>What is my purpose
To kill yourself

>> No.9264835

>tfw i get legitimately blindingly enraged when I get stuck on a problem for too long

>> No.9264839

Why isn't the earth perfectly flat?

Shouldn't the north pole sag down to make it flat? Like with tectonic plates

>> No.9264840
File: 51 KB, 200x200, 1501018980644.png [View same] [iqdb] [saucenao] [google]


>> No.9264883

>Shouldn't the north pole sag down to make it flat?
Why would it? Gravity pulls toward the center of the earth.

>> No.9264888

Is EE really as bad as its famed to be? I find the topic incredibly fascinating but I question whether I'm intelligent enough to make it. I was thinking of going to college this next semester, but I'm worried about being overwhelmed. I have a very poor math education and a lot of catching up to do.

Does anyone have any textbooks or resources you'd recommend so I can get an idea of what I'm in for?

>> No.9264894

Wait.... so big head ed is not a meme?

>> No.9264903


So gravity pulling the sides is why it's pushed up to make the dome on top?

Like a carpet?

>> No.9264908
File: 24 KB, 400x382, 1500484867942.jpg [View same] [iqdb] [saucenao] [google]

No. I attended one of his conferences on paracompactification of the moduli space of connections for [math]N = 2[/math] superconformalsymmetric string theory and his head was so big that I wasn't able to take down any notes at all.

>> No.9264910

bumping this. using C# btw

>> No.9264958



Can someone quickly derive this formula in this video at 26:05 where he goes from the halves to the 2 minus the exponentials? I know that he's trying to get the real parts of the exponential, and to do so he has to add another exponential of opposite sign. I don't understand why both exponential terms are negative (one must be rotating one way, and the other in the opposite direction)..

Besides that, how does he get from the halves to the next part? It's basic integration, I get it, but based on the rules I know so far I can't get it.

>> No.9265021

How come sometimes you have to pee really bad, but when you finally do there's a lot less than you expected?

>> No.9265025

On Thursday I'm going to take the Mercedes 4Matic exam, what should I expect? Have any of you taken it before?

>> No.9265026

Fucking autocorrect, I mean the AMATYC exam

>> No.9265110

How do i calculate the volume of a unit cell with a two atomic basis ?

>> No.9265246
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Reposting since I posted in the dead thread.
I'm supposed to prove [math]\int \int \int_{E}f(x,y)dxdy[/math] exists and calculate its value. What I thought I'd do was calculate the integral for the [math]x^2+y^2\leq z^2+1[/math] side and substract the integral for the [math]2z^2\leq x^2+y^2[/math] side, but since I get [math]\sqrt{x^2+y^2-1}[/math] I'm stuck.
Does [math]\int \int \int_{E}f(x,y)dxdy[/math] actually exist and if so, how should I solve?

>> No.9265422

Alright, hoping some cunt will help me.

Don't know much about chemistry but am tackling a predictive problem which involves finding the amount of aromatic compounds found in diesel fuels.

Why is this useful to be predicting this? In the context of diesel fuels of course.

I've done a bit of research and aromatic compounds are apparently especially stable; so maybe you want less of them in your diesel fuels because less aromaticity means less stability; more reactivity - therefore a more energetic combustion?

Am I close? Completely wrong? Does it have no real useful effect on diesel fuels and I'm just predicting the aromaticity for the sake of it?

>> No.9265451

How do I prove that [math]( f \circ g \circ f)[/math] bijective is equivalent to [math]f[/math] bijective?
Would [math]g[/math] then also have to be bijective, or can it be anything?

>> No.9265453

>this level of reddit spacing

>> No.9265461

I thought it would be a bit more readable this way; feel free to copy it all and remove the line breaks though

>> No.9265481 [DELETED] 

Pretty sure g being injective would be enough.

>> No.9265483 [DELETED] 

sorry, I meant surjective

>> No.9265487

Are MIT calc lectures good enough for a first course in calculus?
Should I complement it with Stewart calculus textbook?

>> No.9265514

Let [math]E\subset \mathbb{R}^n[/math]. Prove that for every [math]\epsilon >0[/math] we can find a succession of closed [math]R_{k}\subset \mathbb{R}^n[/math] such that [math]E\subset \bigcup_{1}^{\infty}R_{k}, \sum_{1}^{\infty}R_{k}<\epsilon[/math] iff for every [math]\epsilon >0[/math] we can find a succession of open [math]A_{k}\subset \mathbb{R}^n[/math] such that [math]E\subset \bigcup_{1}^{\infty}A_{k}, \sum_{1}^{\infty}v(A_{k})<\epsilon[/math].

If we have an open [math]A_{k}[/math] succession like that we only need to close its terms to find the closed [math]R_{k}[/math] succession, but can I prove the converse?

>> No.9265519

take g = 0 for example, then f(g(f(x)) = f(0) for all x, which isn't bijective unless f is only defined on one element

>> No.9265533

No lecture is ever better than a textbook.

>> No.9265543

how do I get rid of ADD, I can't focus longer than 10min at a time studying something

I did not used to be like this

>> No.9265707
File: 1.22 MB, 540x304, Question.gif [View same] [iqdb] [saucenao] [google]

What is that dual-way arrow thing in mechanics, I always see it when I'm working with restitution and collisions but never know what it actually is. You know the <->, what is it called and what does it do?

>> No.9265709

but that is true. That's why most people study ideals as modules. This is by far the approach which is generalized the most (sheaf of ideals, etc.). Things get nasty when you are interested in rings with unity and start considering homs which don't preserve them (e.g. direct limit of rings with unity won't even have to have unity).

>> No.9265827

>A separator N is minimal if N\{i} is not a (k, x)-separator
What does N\{i} means in mathspeak? N is a subset.

>> No.9265828


be warned that throughout wikipedia, the incorrect definition of a ring is used (although to its credit it does specify that there is one other (the correct) definition of rings, which it does not use).

>> No.9265858

Alright sci
Help me with this exam problem
"Find the volume by rotating the region bounded by [math]y = cos x[/math] and [math] y = x [/math] around the x-axis."

No calculators, no shit.
How can I solve this?

>> No.9265899

N excluding i. The subset of N containing all elements of N but i.

>> No.9265915

>No lecture is ever better than a textbook.
Which college for brainlets do you go to?

>> No.9265963

In probability, if a question asks something like:
"What is the probability of x happening *at least once*?"
does this include it happening 0 times?

So for instance A = a man his a target at least once.
P(0 hits) = 0.2963)
P(1 hit) = 0.4444
Would P(A) = 0.2963 + 0.4444?

>> No.9265966

>In probability, if a question asks something like:
>"What is the probability of x happening *at least once*?"
>does this include it happening 0 times?
No, that would be "at most once" (<=1)

At least once is (>=1)

>> No.9265971

At most once is what I meant
So 0.2963 + 0.4444 is at most once right?

>> No.9265973

>So 0.2963 + 0.4444 is at most once right?

>> No.9265978

Was just offered a job In Oklahoma $65k base pay once I graduate this coming December. Ill have to leave all my friends and family though. Is the money worth it.

>> No.9265983

how many golf balls to equal the mass of the sun in kilograms?

>> No.9265987

1.989e30 kg/0.04593 kg

>> No.9265997

All universities are filled with brainlets (the only difference is their parents' money) and professors have to deliver to them.

>> No.9265999

>All universities are filled with brainlets (the only difference is their parents' money) and professors have to deliver to them.
Which college for brainlets do you go to?

>> No.9266010

Imagine believing this.

>> No.9266013

Depends on your field of work and how good of a candidate you are; knowing nothing else about you I would take it.
65k in a low-CoL area is pretty good entry-level for the majority of fields and only the top handful of students in each field can really afford to be picky about starting jobs.

Relocating after college is almost the norm anymore.

>> No.9266027

I really like the MIT lectures
but it does not have a lot of exercises and problems

>> No.9266044

Is the following true: If [math]a_n\to a[/math] as [math]n\to\infty[/math] and [math]\forall n(a_n\in X)[/math], then [math]a\in X[/math]?

[math]a_n=1/n\,;\ X=(0,\infty)[/math] seems like counter example, but i dont know if i'm misunderstanding something

>> No.9266045

>an=1/n; X=(0,∞) seems like counter example
You are correct.

>> No.9266049

Dumb probability question:
P(A) = 1/3\
P(B) = 2/3\

{BBB, BBA, ABB} = (\frac{2}{3} ^3) + ((\frac{2}{3} ^2) * \frac{1}{3}) + ((\frac{2}{3} ^2) * \frac{1}{3}) = 0.59332
That's what I got. Is that correct?

>> No.9266051

I'm shit at latex
{BBB, BBA, ABB} = ...= 0.59323

>> No.9266133

Appreciate it anon

>> No.9266147

This is true if and only if X (metric space) is closed.
For general topological spaces "<=" holds, but not necessarily "=>".

>> No.9266149

See also here:

>> No.9266160

is there anywhere i can ask brainlet-level questions and get a response quickly?
the majority of the questions i have are simple yes/no answers but it's always hit or miss here it seems.
an irc for it would be perfect.

>> No.9266218

How do you solve a boundary value problem using Green's Function when y(0) = 1 and y'(0) = 0?
When I set up my two integrals, what should they be equal to? 0 < t < x and then x < t < 0 i'm pretty sure is wrong.

>> No.9266252

Here's my stupid question:

The inner Earth is hot because of pressure, right? But how does that not violate the laws of thermodynamics? It just seems like it'll keep creating heat forever without having another energy to turn into it.

>> No.9266305
File: 41 KB, 483x473, 1506616234119.jpg [View same] [iqdb] [saucenao] [google]

I have just begun my study of physics at university level. My professor was not aware Scotland slowed down a photon beam.


She said to the class that nothing moved faster than the speed of light and that it's speed was constant. My social anxiety made me hold my tongue, but I later emailed the article to her to show her that is wrong. I realize that classic physics and quantum physics are very different fields, but this woman has a masters and was unaware of the fact. She later told us that Newton's equation for gravity was also wrong and offered Einstein's which is based on light being constant. My question for anyone who has pursued physics is to what extent am I going to be learning things during my studies of physics which are fundamentally wrong? What are those things?

>>TL;DR What basic physical principles or equations taught early on in college are wrong??

>> No.9266307

You literally just said classic and quantum are two different fields. Do you even know what the two are? Start there.

>> No.9266331

Can you prove it?

>> No.9266337

just expand (n-1)(n+1) brainlet

>> No.9266356


>> No.9266358

I get the factoring I’m just asking why one less than a number squared is equal to the product of one more than and one less than that number

>> No.9266359

(on non-compact spaces)

>> No.9266366

just expand the product of one more than and one less than that number brainlet

>> No.9266373

Actually in the trivial ring [math] \{0\} [/math], zero is both the mutiplicative unit and the additive unit. (it's a shit ring to begin with but that doesn't stop it from having this property, it's the only ring that can have this property).

>> No.9266376


>> No.9266378

>Actually in the trivial ring
You are trivial.

>> No.9266381

Feeling repetitive? Maybe you can use words to convince me that this is so.

>> No.9266383

You are being a cunt. There are plenty of text that (espec older) that don't define rings as having multiplicative units. Thats why most texts that deal with rings says things like "in this text we will by a ring mean a ring with a multiplicative unit, unless otherwise specified".

>> No.9266400

where would be a good place to learn about image recognition, for practical purposes? I'm primarily interested in simple geometric shapes and colors. The most computer science I know is Java, so when I tried to read wikipedia it was too much new information to get anything useful out of

>> No.9266413

Make a n+1 by by n-1 square grid with dots. (e.g. 5 from left to right, 3 from top to bottom).
Remove the first row (n+1 dots) and adjoin it vertically next to the first column (n-1 dots).
Now you have a n by n grid with 1 dot sticking out.
Therefore (n-1)(n+1)=n^2+1.

>> No.9266418

>no induction

>> No.9266419

so explain black holes and infinite mass. wouldn't that mean infinite gravity?

>> No.9266449

Not bad. Good job.

>> No.9266451

I am not a physicist so I won't ask about explaination. From pop science it seems many worlds is more popular amongst physicists than the Copenhagen interpretation. My question for you all is: is that an accurate picture to paint?

It just seems more complicated without explaining anything additional.

>> No.9266455

I got a question for all yall smart motherfuckers.. Need only the smartest neebas on this board to answer

Is it possible that a two dimensional being(s) exist? if yes, could they probably get addicted to drugs?

>> No.9266463

This question lacks depth

>> No.9266466


i said smartest people on the board, answer

>> No.9266470

How do I find the best possible item given multiple factors and varied importance of said factors?

Let's say I'm grading apples by Redness, Sweetness and Size. The scales are arbitrary (Redness 0-10, Sweetness -200 - 200, Size 1-100), and each factor is weighted differently (Sweetness is 30% more important than Size, which is 50% more important than Redness).
I want to give each apple a final score that correctly describes this relationship, so that I can mathematically pinpoint which apple is closest to perfect.

How do?

>> No.9266494

you could reduce everything to a common variable then optimize it

>> No.9266498
File: 985 KB, 1034x1989, babaa_scattering.png [View same] [iqdb] [saucenao] [google]

Something like [math]\overleftrightarrow{\partial}[/math]? This means
\hat\psi \overleftrightarrow \psi = \hat\psi \partial \psi + (\partial \hat\psi)\psi

>> No.9266509

Meant [math]\hat\psi \overleftrightarrow{\partial}\psi[/math] on the left.

>> No.9266510

I'm not sure how to go about doing that, and I'm going to need it to be tweakable. Preferably something I can do algorithmically, because I'm not 100% decided on what the weights of the variables are going to be, and I'll need to see how things shake out as I tweak things.

I feel like simply reducing the variables is an over-simplification that won't properly express the data, but I could be wrong.

>> No.9266522

Been working on this for a little while. Starting to feel like I'm at the end of my rope...I was able to reduce it to

[eqn]1/(2*\sqrt{3}*\pi)\int_{-\infty}^{+\infty}\int_{-\infty}^{+\infty} e^{-1/3(x^2 -xy + y^2 -2y +1)}dxdy = 1/2 \int_{-\infty}^{+\infty}e^{-1/3(x(x-u)}dx[/eqn]

where [eqn] u = y-1[/eqn]
But I'm wondering now whether I'm even on the right track

>> No.9266524
File: 40 KB, 813x250, Screenshot_41.png [View same] [iqdb] [saucenao] [google]


>> No.9266527 [DELETED] 

Sorry, this should read
[eqn]1/(2\sqrt{3}\pi)\int_{-\infty}^{+\infty}\int_{-\infty}^{+\infty} xe^{-1/3(x^2 -xy + y^2 -2y +1)}dxdy = 1/2 \int_{-\infty}^{+\infty}e^{-1/3(x(x-u)}dx[/eqn]

where [eqn] u = y-1[/eqn]

>> No.9266532

Should actually read
[eqn]1/(2\sqrt{3}\pi)\int_{-\infty}^{+\infty}\int_{-\infty}^{+\infty} e^{-1/3(x^2 -xy + y^2 -2y +1)}dxdy = 1/2 \int_{-\infty}^{+\infty} x e^{-1/3(x(x-u)}dx[/eqn]

where [eqn] u = y-1[/eqn]

>> No.9266533

Why is there a u in the right hand side but no du?

>> No.9266537

I integrated out the integral with respect to y - 1 = u

>> No.9266548

>I integrated out the integral with respect to y - 1 = u
Why is there a u in the right hand side if you already integrated with respect to u?

>> No.9266571 [DELETED] 

Because I rearranged the equation with a term of the form
[eqn] \int_{-\infty}^{+\infty}\int_{-\infty}^{+\infty} \frac{1}{2\sqrt{3}\pi }e^{-\frac{1}{3}x(x-u) + u^2} dxdu [/eqn]

>> No.9266575

I rearranged it to look like this:
[eqn] \int_{-\infty}^{+\infty}\int_{-\infty}^{+\infty} \frac{1}{2\sqrt{3}\pi }e^{-\frac{1}{3}(x(x-u) + u^2)} dxdu [/eqn]

>> No.9266588

yes, exactly what you wrote... how does the b go there?

>> No.9266603

s\pw %$t\vpw pw\}pw (~{\{p\rwtt |~p$x s\pw
*tw\wt$ }t\pw$\ypw p\rwx} %{~\rwx} rw&~
spw\}t$\%$p pw\}pw (~{\{p\rwtt qx\$~\sxw
r{p\vx\pxw s+tw (~{\{p\rwtt vpw *tw\wt$
p\rwx} ytwp }t\pw$\ypw spw\}t$\%$p z{t$w
%wp}\+xt (~{\{p\rwtt vpw s\pw p\rwx p\rwx}
z{x++xt s\pw %{~\rwx} rw&~ }p$w\s~xt\%$~
p\zwp }~\sp\xw vpw *tw\wt$ sxqtw %$t\vpw
p\zwp pw\{~$+ p\rwx p\rwx} qp\v~$wx
spw\}t$\%$p pw\ypw qt\{p\$p}p sxqtw pw\ypw
%$t\}x{{ |p\t s\pw pw\ypw vpw (~{\{p\rwtt qt
s+tw |~p$x }p$w\s~xt\%$~ %zx} p\rwx}
pw\}pw spw\}t$\%$p pw\ypw p\ztw\sx\v{x}x
%zx} p\ztw\sx\v{x}x (~{\{p\rwtt

Need help with this cypher because I'm a brainlet. Any help?

>> No.9266604

>s\pw %$t\vpw pw\}pw (~{\{p\rwtt |~p$x s\pw
>*tw\wt$ }t\pw$\ypw p\rwx} %{~\rwx} rw&~
>spw\}t$\%$p pw\}pw (~{\{p\rwtt qx\$~\sxw
>r{p\vx\pxw s+tw (~{\{p\rwtt vpw *tw\wt$
>p\rwx} ytwp }t\pw$\ypw spw\}t$\%$p z{t$w
>%wp}\+xt (~{\{p\rwtt vpw s\pw p\rwx p\rwx}
>z{x++xt s\pw %{~\rwx} rw&~ }p$w\s~xt\%$~
>p\zwp }~\sp\xw vpw *tw\wt$ sxqtw %$t\vpw
>p\zwp pw\{~$+ p\rwx p\rwx} qp\v~$wx
>spw\}t$\%$p pw\ypw qt\{p\$p}p sxqtw pw\ypw
>%$t\}x{{ |p\t s\pw pw\ypw vpw (~{\{p\rwtt qt
>s+tw |~p$x }p$w\s~xt\%$~ %zx} p\rwx}
>pw\}pw spw\}t$\%$p pw\ypw p\ztw\sx\v{x}x
>%zx} p\ztw\sx\v{x}x (~{\{p\rwtt
That's not a cypher, it's just jibberish.

>> No.9266608

I wouldn't be so sure.

Also, the hint included is Ouroboros

>> No.9266609

>I wouldn't be so sure.
I am.

>> No.9266613

I'll take your word for it.

>> No.9266633

Can somone give me the homotopy?

>> No.9266638
File: 2.69 MB, 4224x3136, IMAG0120.jpg [View same] [iqdb] [saucenao] [google]

Forgot pic.

>> No.9266642
File: 212 KB, 645x960, test (6).jpg [View same] [iqdb] [saucenao] [google]

Sorry only got holonomy here.

>> No.9266678

Does [math]x\cdot|x|=x^2[/math]?

>> No.9266680

nope. sps x = -1

>> No.9266690


why does it shatter like this? after being shot so many times, eventually it shatters like glass.

first it bends, then it shatters. it's like a cross between metal and glass. Is it better for body armor to be crystalline or amorphous and which one is this?

>> No.9266692

That's a deformation retract of a doubly punctured disc and deformation retracts don't affect the homotopy.
[math]\pi_1(D \setminus \{x_1,x_2\}) = \pi_1(S^1 \wedge S^1) \cong \mathbb{Z} \otimes \mathbb{Z}[/math]

>> No.9266696

Do you mean Z+Z ?

>> No.9266698

I´m actually in intro to complex analysis and I don't have a single clue about algebraic topology, but I have an exercise In which I need to construct a homotopy bewteen the bigger circle and the smaller one. I just have in the bag the definition of it.

>> No.9266700

Has anyone taken the GMAT? How difficult is the math?

Should I go back and review holistically (I haven't done anything related to higher math in around a decade) or should I study specifically for the test?

>> No.9266701
File: 212 KB, 341x444, ran_srs.png [View same] [iqdb] [saucenao] [google]

No. I meant the free group upon by 2 elements.
>actually construct the homotopy
Do people actually still do this?

>> No.9266714

Ok but you wrote the tensor product, which isn't right.

>> No.9266720

I suppose it's just a non trivial constructión in this case. My problem is that the just uses the convex sum of the curves but it gives a weird parametrization of the unit circle so it has some weight in the parameter. Basically he first finds a [math]k, \vert \frac{1}{2}+ke^{is}\vert^2=1[/math] which gives [math]k=\frac{\sqrt{cos^2s+3}-coss}{2}[/math] But this only works for [math]s\in [0,\pi/2][/math]. Then I'm asked to construct the parametrization for [math]s\in [\pi/2,\pi] [/math] Which I belive needs to have a similar weight, but in [math] \gamma(s)=1[/math] which overshoots as I belive the points directly above the inner curve needs to go at the same rate as the normal parametrization of each component of that inner curve as in the section [math][o,\pi/2][/math] the book gives your typical circle parametrization.I'm at a loss.

>> No.9266742
File: 2 KB, 288x216, paint.png [View same] [iqdb] [saucenao] [google]

Oh wait I fucked up. That's not correct
Take from the row/column with the n-1 dots. Adjoin to the column/row of the n+1 dots.
If you add a new dot then you get a n by n grid.

>> No.9266767


>> No.9266770

Why do radiography courses take 3+ years? I know colleges like to drag shit out for money but it seems excessive.

>> No.9266781

The reason for this being ZxZ is because you have two holes you can loop around. It's that simple. If you take any loop then you can deform it to any other loop that goes around the two different holes the same number of times.

>> No.9266788


it can be derived from the original definition of the factorial

f(x+1)=f(x)(x+1) given f(1)=1


god i need to learn Latex

you can also define it from the Gamma Function tho, Id guess that someone found it from the recursive definition before someone even found the Gamma function

>> No.9266791

If x=-1 that equality doesn't hold.

>> No.9266802


its impossible for 2 dimensional beings to exists in our universe

>> No.9266817

how come everyone can see the moon at night? how fast does the moon orbit the earth? does it orbit the earth at an opposite direction to earths rotation? if there is a slar eclipse then what happens with the side of the earth where its currently night time, is the moon visible?
Imean it has to orbit in an opposite direction or a completely different speed otherwise the moon would be onlky visible at some places, what happens t the poles? is the moon always visible there? is it never visible there? none of this makes sense to me how does the moon really work?

>> No.9266819


learning latex is easy and fun to do! I recommend it.

t. brainlet who can't even code but is competent in tex

>> No.9266823

come to think of it how the fuck is mercury visible at all

>> No.9266824

It takes 27 days for the moon to rotate around the Earth once (sidereal month).
The moon orbits in the same direction as the Earth rotates. The moon is not visible from the night side of the Earth during a solar eclipse. I think the axial tilt (and the orbit of the moon) makes it so the moon does not rise at certain times of the year at the poles.

>> No.9266826

certain times of the year Mercury is visible for a short period of time just before the sun comes up (in the northern hemisphere, maybe in the southern too)
It's like only half an hour or something

>> No.9266828

you didnt answer the most important question

>> No.9266829

Which one?

>> No.9266831

how come the moon is always visible at night anywhere but the poles unless there is a solar eclipse
isit just a coinsidence because it has the perfect speed to always be at the oposite end to the sun?
that doesnt make sense either, if it rotates then there should always bee solar eclipses because it must constantly cross paths with the sun

>> No.9266833


The term of art is /prograde orbit/, as opposed to retrograde.

>> No.9266834

* there hould be at least one solar eclipse every 27days

>> No.9266841

The orbit of the moon is tilted relative to the ecliptic (the earth-sun orbit) so a total solar eclipse is only possible twice a year and because of the eccentricity of the Moon's orbit a real total solar eclipse happens even less often (iirc)

>> No.9266843

I know for PhD applications that research experience and letters of recommendation are the most important, with GPA and GRE score being slightly less important, but how is it for MS applications? I've heard research isn't required, but does it significantly help to have research experience over other applicants? Or is it actually just grade based and some teacher saying "yeah he was a good student sure"

>> No.9266845

ok but hear me out
in order to see the moon at night the moon must be at the opposite side of the planet to the side thats iluminated by the sun at all times
otherwise there would be a lot of moonless nights

>> No.9266846

All graduate programs I've seen need at least two letters or recommendation and a certain average, that's the bare minimum

>> No.9266849

There are moonless nights, it's called the new moon phase

>> No.9266852

i feel stupid for never notticing this

>> No.9266856

Don't I'm puzzling over it a bit too, it seems like there would be more moonless nights than just one a month

>> No.9266864

also how is it always the same cycle? we dont use a moon based calendar

>> No.9266872

what are you asking? And we kind of do use a moon based calendar, a sydonic month (like 31 days) is how long it takes for the moon to show the same phase and is longer than a sidereal (star) month (27 days). The months just have different lengths so they can add up to 365 (plus some) days a year (I think).

>> No.9266874

the sydonic months are probably totally out of phase with the calendar months now but not in ancient times

>> No.9266875

it makes sense if its a moon based calendar, otherwise we could get two moonless nights some years in october because its 31 days long and it takes 27 days to orbit the earth

>> No.9266881

I'm not actually sure if it's possible to show two of the same phases in one month but it seems like something that happens like once every 200 years or something

>> No.9267053

Since there were many more than three variables in my data set, and at least two of them were somewhat subjective, the solution turned out to be a modified version of Analytic Hierarchy Process. I wrote a quick program to calculate the weighted and unweighted averages of various variable pairs, and then the pairs against one another, and then had it iterate through a few thousand times while scaling the subjective variables back and forth across reasonable bounds.
A clear pattern of best options emerged from the data points I shotgunned against the wall, and subsequent testing backs up the results.

I still wish I knew a clean and quick way to do this as it's not exactly something I could do on the back of a napkin - but when it doubt, brute force it out.

>> No.9267202

Pls halp

>> No.9267212

Ops I forgot to say that x >= 0

>> No.9267215

This is one of the best threads on the internet. It has greatly helped me in the past. It's not much of a reward, but I want to thank all you faggots ITT and in past threads that help us brainlets.

>> No.9267229

In which position would I have to deal with more egotistical fuckwit coworkers, doctor or rad tech?

>> No.9267266

How would you find out of two events are independent of each other using just the content of their sets?
I.e. not by using their probabilities

>> No.9267275

Use cylindrical coordinates (considering the x-axis as the z-axis; z_o is the first positive solution of z = cos(z)) [eqn] V = \int \limits_{\theta = 0}^{2 \pi} \int \limits_{z = 0}^{z_o} \int \limits_{\rho = z}^{\cos z} \rho \,d \rho \,dz \,d \theta [/eqn] Not sure if it's correct but you'll get something similar anyway.

>> No.9267378

I'm sorry but I don't understand your solution
I don't know how to do 3 integrals at the same time too
I know basic integral (trig substitution, u substitution, etc)

>> No.9267388

it's just a fancy way of writing the washer method, he didn't solve what the hell x = cosx is which is really the true kicker to the problem, best I can do is approximate it as sqrt(3)-1, and after briefly looking around online , that seems to be the best you're going to get

>> No.9267437
File: 37 KB, 500x495, 1499723660864.jpg [View same] [iqdb] [saucenao] [google]

I am 1/4 way through my masters.
I am getting scared it is ending too soon.
One way of stalling is to do an honors for my undergraduate.
It would give me an addition dissertation+4 more elective units from my specialization.
It would take an extra year of my time (good/neutral)
and cost my $6000 (kind of bad).

Should I do it, I don't think I wan to go into the real world yet.

>> No.9267477

suppose [math]f : E \rightarrow F [/math] and [math]g : F \rightarrow E [/math], if [math] (f \circ g \circ f)[/math] is a bijection, is [math]f[/math] a bijection? How does one prove this?

Is this a coincidence or were you sitting in the same lecture hall as I was, scratching your head when the prof said this was trivial...?
At least ask the question right, you clucker.

>> No.9267528

Let's prove an equivalent proposition: if f is not a bijection, then fogof is not a bijection.
If f is not injective, then for distinct x,y in E you have f(x)=f(y), which means gof(x)=gof(y) and fogof(x)=fogof(y), so fogof is not injective and therefore not bijective
If f is not surjective, then there are elements in the codomain which are not in the image of f, so fogof is not surjective and therefore not bijective.

>> No.9267532

If their intersection is the null set.

>> No.9267561

It's not.
One is a subset of the other. (A {a,b,c}, B{a.b.c.d})
Does that mean they are dependent on one another?

>> No.9267564

Real life is 10x better than school.

>> No.9267592

Do quantum mechanics imply the universe is not deterministic?
As I have understood it, with my bias, that "non-determinism" is only relevant or true when it comes to our attempts to measure/observe events.
But many people seem to say that there really is "non-determinism". That truly random events and non-causal outcomes happen in reality.

What's the truth about this? Is the universe really "random"?

>> No.9267600

I guess the question is wrong then.
Thank you, anon

>> No.9267610

If event A is a subset of event B then event B happening implies event A happens so they are dependent (but only one way)

>> No.9267612

If their intersection is empty, then they are dependent as fuck. One event happening excludes the other.

>> No.9267616

>One event happening excludes the other.
that's what independent means iirc
am I wrong?

>> No.9267625

Yes of course they are.
Generally, two events A and B are dependent if and only if one gives information about the other.
i.e. P(A happening given B happening) is not equal to P(A happening) or equivallently P(B given A) is not equal to P(B).

>> No.9267626

>am I wrong?
yeah, see >>9267625

>> No.9267772

Did a simple Baye's problem for a question, but the third part is basically doing it backwards.
In short:
P(A) = 1/3
P(B) = 2/3
P(C|A) = 1/10
P(C|B) = 1/5
P(C) = (totality) = 0.1666

But the third part has said P(C) is revised to 1/8.
How would P(A) and P(B) be revised to account for this, assuming P(A) must have the "smallest proportion" out of A and B?
I'm guessing that means P(A) must be the smallest possible amount.

>> No.9268170
File: 37 KB, 604x116, p7.png [View same] [iqdb] [saucenao] [google]

Can anyone help me with this proof. I know with the hints it should be easy. It is a stupid question thread after all.

So my plan was to assume the worst possible case.
A stack of n pancakes in which none of them can be glued together.

Does anyone have any resources that might be helpful for the pancake problem or pancake numbers?

>> No.9268260

do axiomatic systems exist in which a finite number of theorems can be derived?

>> No.9268267

The point of what he said is that there is no purpose to life. Make one your own, but it isn't going to matter.

>> No.9268291

sure, but only in a very abstract sense.

You can think of any rewrite system as an "axiomatic system", and think of any "derivable expression" as a "theorem". In that sense, you could make an "axiomatic system" which just has a start symbol S which rewrites as any number of things in a finite list, and that gives an example.

In practice though, no. Even if your logic just has conjunction, if you can prove phi, you can prove phi & phi, phi & phi & phi, etc. though maybe you are really interested in something weaker, like "finite number of theorems, mod being provably equivalent". Then again, yes, just take any classical propositional logic with only finitely many propositions.

>> No.9268365

Black holes don't have infinite mass.

>> No.9268475

Ok /sqt/ I'm fucking stupid at Linear Algebra
I don't understand Vector Spaces and all of this shit
Please help. Do you guys knows a good book/lectures/whatever to help me?
I tried MIT lectures but I don't understood them

>> No.9268483

>I tried MIT lectures but I don't understood them
That's because they are shit.
Try Axler's book. It's really well-written.

>> No.9268641

You guess. That's it. You need it to dominate the original function to actually interchange limits but that's usually not a problem.

>> No.9268698

They're all wrong since we don't have a set of postulates that predicts all physical phenomena yet. Also nothing moves faster than light in a vacuum. Light slows down in air because it can no longer move in a straight line. It bounces around so it "travels" slower through it.

>> No.9268720

I recently read something interesting that ties into this so I'm sharing it.

Imagine the food chain before humans asserted themselves into the top of it.

The lion hunts down and eats 80% (I'm pulling the number out of my ass) of the meat.
Vultures eat the remaing 19%.
How can humans survive if other predators have clear advantages? A lion can run behind and kill with its teeth, the vulture can pick up left meat from the ground and get away without much trouble. The human? The human does not have sharp teeth or wings, but he uses tools to break into the left bones of animals, which contain inside bone marrow, a food source that is not exploited by other predators.

After humans started to use their intelect instead of instincs to be better predators they asserted themselves into the top of the food chain.

That is your purpose. As a human your purpose in life is to use tools in order to break into bones of animals. Or at least was until we, not only asserted ourselves into the top, but also made sure to get a limitless amount of food that is easily accesible, effectively eliminating our purpose in life. Now because we are the animal on top, and the one who does not worry as others of survival, your purpose in life is whatever challenge/goal you set yourself. Anon, remember that the greatest gift in life is the chance to make a difference, no matter how small or big impact you think it will have, it is a great gift. Have that in your heart and when you are given the magnificent gift do not shy away from it.

>> No.9268737

Some time ago an anon here was posting some art related to topology. For example, one of them was a hand covered with holes. It was titled cohomology or something like that. Does anyone have a link to those pictures?

>> No.9268743
File: 1.52 MB, 1907x2906, 9r0oMNl.jpg [View same] [iqdb] [saucenao] [google]


Fomenko's "A space with nontrivial local homology" [1967]

>> No.9268746

Holy shit that was fast. Thanks a lot!

>> No.9268760
File: 95 KB, 852x591, ada.png [View same] [iqdb] [saucenao] [google]

Can anybody help me understand the proof of 1)? Why does this prove that the pre image of Q is finite?

Alternatively, can anybody link me a good proof for the Riemann-Hurwitz Genus-Degree formula?

>> No.9268802


Maybe f mapping infinitely many points into point means it is constant?

Or: The last statement says that the infinite subsequence {P_n_i} which are all distinct converges to P. Then for P_a \neq P_b \neq P, we have P \in Neighborhood(P_a) and P \in Neighborhood(P_b). But these are Riemann surfaces which must be Hausdorff, so distinct points must have disjoint neighborhoods. This is a contradiction.

>> No.9268815

Say I have two rows of data, one with the success rates of certain tests and the other with the number of attempts, how would I measure the quality of the results in a way that lets me identify the test that worked "best"? For example
>Test 1: 50% success rate, 250 attempts
>Test 2: 60% success rate, 100 attempts
>Test 3: 55% success rate, 500 attempts
Test 2 has the highest success rate, but fewest attempts, so the results may be less meaningful than those of Test 3.

>> No.9268844
File: 103 KB, 720x478, dardy as boa.jpg [View same] [iqdb] [saucenao] [google]

Are sample proportions and binomial distributions essentially the same thing? How do they differ?

>> No.9268858

What's a good book to learn complex analysis? I'm a physics student not a math student so I don't know shit about topology

>> No.9268934

What was the name of that bacteria that was supposed to have a different element in its DNA?
(I know the experiment was done wrong)

>> No.9268945


>> No.9268969

Find a natural predator for moths and stick it inside your ass, once it's done pull it out.

>> No.9269001

What if f isn't injective? What can you say about fgf? What if f isn't surjective?

>> No.9269030

Is there some operator like modulo, but there aren't any zeros outputted?

Rather than (with 1 to 6, m = 6)
0 1 2 3 4 5 0 1 2 3 4 5 0 1
You get
1 2 3 4 5 1 2 3 4 5 1 2 3 4

>> No.9269084

modulo + 1

>> No.9269088

Yeah I literally just spotted this, fuck me I really am making this a stupid question thread

>> No.9269093
File: 2 KB, 297x297, shitnignog.png [View same] [iqdb] [saucenao] [google]

so i know that if there is a base, an sn1 can occur, and i will get a racemate

my question, is an e2 also possible here?

>> No.9269165
File: 9 KB, 816x1056, what.jpg [View same] [iqdb] [saucenao] [google]

what is the length y, which propositions did you use?

>> No.9269174

If you use the right base and reaction conditions, sure
shit like this is always heavily dependent on the base and reaction conditions used (solvent, temperatur etc)

>> No.9269177

thats what i was thinking, thanks babe

>> No.9269179

also remember that the preferred conformation of this molecule already has hydrogens in the axial positions
you have the right geometry aligned already, the problem might just be br- being too good of a leaving group but that should be solveable with the right conditions

>> No.9269264

the light went trough a special mask you shithead

>> No.9269276

>sample proportions

>> No.9269306

If I have a Set S and this set is empty but I make a Statement about S saying all elements are bigger than 5 is my statement true or false?

I could say I cant find an element in S for which that is not the case, hence it's true but I also cant find an element for which that is the case, hence the statement is also false.

>> No.9269311

>If I have a Set S and this set is empty but I make a Statement about S saying all elements are bigger than 5 is my statement true or false?

>> No.9269312

nevermind I got it myself. The elements for which my statement is true are irrelevant it's about the elements for which it's false

>> No.9269316

Can an Atom of (for example) Carbon which atomic number is 6, have less than 6 neutrons?

>> No.9269323

thank you very much

>> No.9269386

Quesstion about solving this differential equation.
(D+1)x + (D-2)y = 5/2
2x + (D-1)y = -2
First thing I did was multiply the first equation by -2, then the bottom by (D+1) to cancel out the x.
My question is what the fuck is -2(D+1) ?
Like what is -2D supposed to be?

>> No.9269393

Maybe I didn't study enough math but I'd like to ask wtf is "D+1"? Like, is it "D" as in derivate? Why didnt you put in capital? Usually it's dx + dy = some other shit, but "D+1" is new to me. I did calculus 1 and 2 (still suck at both and didn't pass either exam)

>> No.9269398

(D+a)x probably means x'+ax

>> No.9269413

It's supposed to be some sort of notation.
When you distribute (D+1)x it's Dx +1x, meaning x' + x

>> No.9269422

I understand that, but what I still don't know what -2(D+1) is.

>> No.9269497


>> No.9269502

[math]\color{orange}{\mathfrak{Here's\ a\ stupid\ question}}[/math]
[math]\color{orange}{\mathfrak{Why\ is\ his\ head\ so\ big?}}[/math]

>> No.9269524

How can you not?

>> No.9269531

That is because a "calculus" course doesn't usually treat a derivative as a linear operator.

>> No.9269549

>That is because a "calculus" course doesn't usually treat a derivative as a linear operator.
Which college for brainlets do you go to?

>> No.9269570

I didn't take calculus at college.

>> No.9269577
File: 32 KB, 620x516, UUbar.png [View same] [iqdb] [saucenao] [google]

this is probably what he was going for on the top there

>> No.9269590

no. he drew exactly what he wanted. it's a graph with 3 edges and 2 vertices, a contraction of the 2-torus drawn below

>> No.9269600
File: 445 KB, 400x463, EmperorOfManyEmpires.png [View same] [iqdb] [saucenao] [google]

he drew what he wanted, but what he drew doesn't represent the interaction he's seeking to describe

>> No.9269634
File: 11 KB, 297x109, magic.png [View same] [iqdb] [saucenao] [google]

Can anyone see why/how we go from having 2*p*cos(theta) to suddenly having two cosine arguments 3*p*cosine theta - p * cosine theta ?

>> No.9269636

> Can anyone see why/how we go from having 2*p*cos(theta) to suddenly having two cosine arguments 3*p*cosine theta - p * cosine theta ?

>> No.9269638

lmao I get it

massive brainlet here

>> No.9269681

Hello /sqt/
Are the Multivariable Calculus lectures at MIT OCW good enough?
I tried to learn with Stewart book but it is pretty bad (but have good problems)

>> No.9269693

Question about this boundary problem i'm trying to solve.
y= c_1x^3 + c_2x^3
y(1) = 1 y'(3) = 1
I found that c_1 = 1 - c_2 when y(1) = 1
I substitute c_1 into y and get y= x^3 - c_2x^3 + c_2x^2
What is my first y_1 supposed to be? I'm going to be using that, and then a y_2 from the other value and put it into green's function, but I feel like there's an error here.

>> No.9269709

yes, they're good.

>> No.9269735

I need to make a java program that has two methods in a class. One method adds 1 to a string's binary and the other method subtracts 1 from a strings binary.
For example, 1011 becomes 1100 when +1 and 1010 when -1.

The thing is, we're not allowed to convert anything to integer or use any built in classes other than String.

We've not went over anything about binary or binary type problems in class, so I'm not sure where to start here.

I found out how to add and subtract binaries on paper. But not being able to convert to anything has me stumped as to what to do.

Not looking for the answer, just some help to get started.

>> No.9269736

thanks buddy

>> No.9269755
File: 8 KB, 244x206, 1469466916876.jpg [View same] [iqdb] [saucenao] [google]


what does all the shit about a smallest positive number existing have to do with [math]\langle b\rangle\subseteq U[/math]?

>> No.9269769

[math](0.1 * x) + (0.2 * y) = 0.125[/math]
How would I find what x and y are?
x needs to be the smallest proportion possible.

>> No.9269773

>what does all the shit about a smallest positive number existing have to do with ⟨b⟩⊆U⟨b⟩⊆U?
Nothing. But it is required to prove the reverse inclusion, which you would know if you read the next few lines of the proof

>> No.9269781

thanks. i thought that but was unsure.
would it make a difference if that stuff was written after the first part then?

>> No.9269787

Not really

>> No.9269791

What I would do under those restrictions for the +1 function would be read the String in reverse order until I find a zero, then save the position where the zero is on an int. That way I have a side of the string which doesn't need to be modified and another side on which I replace the zero for a 1 and all the 1s for 0s.
The -1 function is about the same, keep reading zeros until you find a 1.

>> No.9269814
File: 1.48 MB, 1600x1195, ZfqmFfN.jpg [View same] [iqdb] [saucenao] [google]

help out a biologie bro

heres my thread


>> No.9269861

With bayesian spam classifiers, are the features things about the email itself? Or features relating to something else?
I've got a question about using naive bayes to discuss a Facebook "interesting post classifier" (i.e. a post is either interesting or not interesting to a user).

What would examples of the features be in this case? The words in the post? Or would it also relate to that person's things like their page likes etc?

>> No.9269898

Although I heavily dislike Khan Academy, they have a video series on Multivariable calculus where half of it (differentiation part) is made by 3Blue1Brown which is God-tier.

>> No.9270023
File: 3.59 MB, 690x388, green_fire_shorter.gif [View same] [iqdb] [saucenao] [google]

Was halfassing some experimentation the last couple of days in prep for Halloween to set up with some green fire for my decorations and kept running into an issue.

Stuff I had on hand:
>sodium-tetroborate (borax)
>boric acid

Mixed the methanol with the borax and was getting a orange/red flame from that, where when I did the methanol and boric acid mix I was getting the green flames I desired.

With the borax mix am I just running into an issue with sodium contamination and it was overpowering the boron and I need to be using much less borax in my solution?

Also I attempted to use sterno cans at one point and had no success with the boric acid or borax, did they change their formulation?

Gif is from last night using a.... I think 6 oz of methanol to 1 oz of boric acid powder mixture (think it was an ounce I was kinda doing this freehand and trying not to blow my eyebrows off)

>> No.9270062

I want to learn topology. The highest lvl in math I got to was polar coordinates in calc 2. what/where do i go from there to topology?

>> No.9270071

why do you want to learn about topology if you have no experience in real mathematics?

If you're convinced: i'd suggest reading something about logic, then modern algebra, then advanced calculus, then analysis, then topology

>> No.9270084

analysis is basically calculus made rigorous by using some topology. just grab a real analysis book

>I want to learn A
>I'd suggest learning B, C, D, and then A

>> No.9270088

of course it's totally posible

>> No.9270090

are you confused?

>> No.9270096

Learn some basic analysis on R, then some basic analysis on abstract metric spaces, then general topology, then topology.

>> No.9270109
File: 5 KB, 379x257, PHY_error_analysis1.gif [View same] [iqdb] [saucenao] [google]

physics freshman here.
If I'm measuring something with a metre stick say to the nearest 1mm, is the error 0.5mm or 1mm? Say I get 169mm, is that 169 + or - 0.5mm, or 169 + or - 1mm?
Or say I'm reading off an oscillator the requency and it gives 52.1Hz, is that with an error of 0.1Hz or 0.05Hz?

>> No.9270114

measurement error would be 1mm, as that's the lowest level of precision available to you.
you could find a statistical error in length by using a number of different rulers and making the same measurement

>> No.9270120

thanks anon

>> No.9270123

How the FUCK do I do this

>A weather channel has the local forecast on the hour and at 10, 25, 30, 45, and 55 minutes past. Suppose you wake up in the middle of the night and turn on the TV. Let X be the time you have to wait until the beginning of the next local forecast, measured in minutes. Find the density function of X.

I can see the relative probabilities of 5, 10, and 15 minute waits but I'm stuck

>> No.9270156

Damn, my brain doesn't want to understand how multiplaying two sequences works.
For instance, I want to multiply the sequences:

( a n ·x n +a n−1 ·x n−1 +...+a 1 ·x+a 0 ) * ( b n ·x n +b n−1 ·x n−1 +...+b 1 ·x+b 0 )

How do I write the product of this?

>> No.9270159

one element at a time.
first element of the first sequence in multiplied by the entire second sequence. then the second element of the first sequence. then the third.

>> No.9270169

I see, I'll try my best. Thanks by the way.

>> No.9270179

How do I find a Riemann sum using a TI-84? I store [math]f(x)=sin(3x)[/math] as [math]Y_1[/math], then I bring up the summation function, but I have no clue how to put in [math]x_k^*[/math], and I especially have to idea what to change when I want to find the RRS instead of the LRS.

>> No.9270189

In my example, I'm trying to find the LRS, RRS, and MRS on the interval [0,[math]\pi/2[/math]]. Not asking for answers, I just want to know how to find it.

>> No.9270198

Can someone explain very simply what a group homomorphism is?

>> No.9270199

the definition is as clear as it gets, bud.

>> No.9270210

it has to do with gays
it has to do with forms

has to do with gay forms

>> No.9270221

I thought it was the engineers who were gay, not the mathematicians.

>> No.9270234

Arbitrary functions are terribly behaved, so we just consider ones that play nicely with the structure of groups. It lets you transfer statements about one group to another, basically.

>> No.9270268

Perhaps it depends on your professor etc. as I have seen varying answers but I can say with certainty that I was taught that the uncertainties would be [math] \pm 0.5mm, \pm 0.05Hz [/math] respectively.

>> No.9270292

It's just how you multiply polynomials
[math] c_0 + c_1 x+ \cdots + c_{n+m}x^{n+m} [/math] , where [math] c_k = \sum\limits_{i,j:i+j=k} a_i b_j = \sum\limits_{i=0}^{k} a_i b_{k-i} [/math]

>> No.9270302

If you perform the operation of G1 on two elements of G1 and then send the result to G2 via f, it is the same as sending the two elements to G2 via f and performing the operation of G2 on their images.

>> No.9270307

Hey /sci/. I'm losing my mind here. There was some way of transforming a fraction with a sum in the denominator into a sum of multiple functions with a single variable in the denominator. I cannot remember the name of this technique for the life of me.

[math]\frac{1}{a+b} = \frac{A}{a} + \frac{B}{b}[/math]

It looks something like that. Please give me a name for this thing so I can google it and learn more.

>> No.9270318


>> No.9270325

A function from domain G to a codomain G' where f(ab)=f(a)f(b)
(a,b are in G)

>> No.9270337

What does the word "explanation" mean to you?

>> No.9270372

why is my chem professor such a spaz when it comes to VSEPR models ?

>> No.9270388

How can I find the volume of a figure such as x^2+y^2=5z^2 from z=0 to 3 using integrals?
I could find it by using the formula V=pi*r*h, but I want to know how to do it using integrals.
I think it would be something like [math]\int_{0}^{3}\int_{-\sqrt{5z^2}}^{\sqrt{5z^2}}\int_{-\sqrt{5z^2-y^2}}^{\sqrt{5z^2-y^2}}dxdydz[/math], how wrong am I?

>> No.9270435

So I was reading a book about control and got to the PID. But I don't understand the I, how is the integral of the error supposed to cancel the noise, if that's what it is doing?

>> No.9270444

so minor update on this, I realized after re-reading the sterno cans they were Sterno "green" made with Ethyl alchohol not methanol....

>> No.9270462

Oh thank God thank you, that's exactly it.

>> No.9270511

think of a function as a translation. not all translations are good. what's good?

multiplying in A, then translating into B is the same as translating operands into B, then multiplying there

>> No.9270566

someone explain to me the subgroup classification of SO(3). And while u are at it, also explain me the symmetries of the polyhedrons.

>> No.9270661

Is it okay to approach a professor (never had a class with) with interest in undergrad research opportunities at this time?(about half way+ through semester) Or is it best to wait until the beginning of a semester?

>> No.9270667

Just go dude. It's pretty much the professor's duty to help on such stuff.

>> No.9271073

If anything, it would be harder to do it at the beginning of a semester. Just go chat with them about what they're interested in.

>> No.9271106
File: 5 KB, 331x225, integral.png [View same] [iqdb] [saucenao] [google]

How did Wolfram get the partial fractions?

I did the steps but I got [math]\frac{x+1}{(x^2+1)^2}[/math] instead of [math]/frac {x}{(x^2+1)^2}[/math]

>> No.9271108

Oh I fucked up with latex
[math]\frac {x}{(x^2+1)^2}[/math]

>> No.9271279

Is a function sum(s), which takes a string of Natural numbers and outputs the sum of the given numbers, such that sum((1,2,3))=6 for example, surjective?

It quite obviously is but how do i structure a proper proof for this?

>> No.9271292

>It quite obviously is but how do i structure a proper proof for this?
therefore surjective

>> No.9271331

i just realized how brainlet i really am

>> No.9271405

That sounds like masochism to me. It's much simpler to change it into cylindrical coordinates. So let [math] x = r \cdot cos(\theta) [/math], [math] y = r \cdot sin(\theta) [/math] and [math] z = z [/math]. The jacobian is just [math] r [/math], so the volume element is [math] dV = r\space dr d\theta dz [/math]. Now the equation is [math] 5 z^2 = r^2 \rightarrow r = \sqrt{5}\space z[/math], a cone. The limits of integration become
[eqn] \int_z \int_\theta \int_r r dr d\theta dz = \int_{z =0}^{z =3} \int_{\theta =0}^{\theta =2\pi} \int_{r=0}^{r=z\sqrt{5}}rdrd\theta dz = 2\pi \int_0^3 \frac{5z^2}{2}dz = 45\pi [/eqn]

>> No.9271412

Don't answer those autists, no one cares except those mentally challenged individuals. Nothing we can do about them sadly as autism is incurable.

>> No.9271453

Hey (((faggots))) , new thread

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