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12:00 AM
@MaryStar we know that the kerB is equal in size to A, but in general no consider the map B maps u to 0 iff u is in image of A else B maps to litter-ally anything except 0
 
So, we cannot say if B is 1-1 or onto, can we? @shaihorowitz
 
So we have $0\to X\xrightarrow AY\xrightarrow BZ$ is exact? @MaryStar
No, $B$ does not need to be 1-1 or onto, I don't believe
 
@MaryStar Not usually, in certain instances we can for instance if there exist only the 0 vector or the space your working in is the same size as ImA, The main point is B can be strictly larger than the image of A
 
Ah ok..
 
Suppose $A:\Bbb Z\to\Bbb Z,x\mapsto2x$ and $B:\Bbb Z\to\Bbb Z_4,x\mapsto\overline{2x}$, for example
where $\Bbb Z_4$ means $\Bbb Z/4\Bbb Z$
${\rm im}~A=\ker B=2\Bbb Z$ but $B$ is neither 1-1 nor onto
@MaryStar
 
12:11 AM
I wish that was rendered in the chat so i could follow... lol
 
@shaihorowitz On the sidebar there's a way to render LaTeX
 
@AkivaWeinberger Your AMAZING
 
Aw thanks
You got it working? $\tau\epsilon s\tau$
 
yep
nice example
@MaryStar Do you understand?
 
So it looks like I can't do that...
 
12:26 AM
it looked pretty confusing, im not used to dx being on the inside of sin, but rather sin(x)dx
 
yup, that's exactly what I find weird
 
now i can actually see it, i didn't know how to render latex before like 5 comments ago. try leaving the omegas in and take the dt to the outside. I'm not to comfortable with what a sin of a infinitesimal but i think it would mean the same thing?
 
I think not. D: . The geometric approach shows that it actually is the sine and cosine of infinitesimals...
BTW it should have the same formulas as in the vid. ($\omega$ is constant)
 
i'm going to be honest with you here
i didn't watch the vid i was thinking about linear algebra
 
12:35 AM
yeah can't do anything that involves volume right now.
 
I'd guess $\sin(dx)\approx dx$
 
that relation HAS to be $\vec{r} = r\cos(\omega t)*\hat{i} + r\sin(\omega t)*\hat{j}$
 
(I haven't seen the video either, but I know $\lim\limits_{dx\to0}\dfrac{\sin(dx)}{dx}=1\\$)
 
@AkivaWeinberger can you show this?
 
cos(dx)/1 as dx goes to 0 = 1
l'hopital's rule I had to google how to spell it
 
12:41 AM
lol
hmm...
 
i'm just going to call it the lhospital rule if thats ok with everyone
 
gotta think about that dt inside of sine/cosine
 
@Chinatsu-creepy-chan It's a famous one; maybe it looks unfamiliar because I wrote $dx$ instead of $x$, but it's the same thing
 
@AkivaWeinberger yup, I forgot I could use L'Hôpital
 
It's essentially $\sin'(0)=1$; use the definition of the derivative on the left-hand side
 
12:45 AM
1 hour ago, by Chinatsu-creepy-chan
and in my attempt I got this: $dr = r\cos(d\theta)*\hat{i} + r\sin(d\theta)*\hat{j}$
1 hour ago, by Chinatsu-creepy-chan
where $ d\theta = \omega \, dt $
 
@AkivaWeinberger I'm not sure i'm comfortable with that because of lack of quotient rule.
so $dr=rcos(omega)∗i^+rsin(w)∗j^dt$
 
$d\vec{r} = r\cos(\omega\,dt)\hat{i} + r\sin(\omega\,dt)\hat{j}$
 
i'm really bad at this latex thing
 
\$\omega\$ $\to$ $\omega$
\$\cos\$ $\to$ $\cos$
 
12:49 AM
ya'll know what i mean
 
\$\hat i\$ $\to$ $\hat i$
\$\hat\imath\$ $\to$ $\hat\imath$
 
in truth i have a cheat sheet whenever i'm writing actual papers
but i'm just at home relaxing
 
Not sure if this works… \$\hat\jmath\$ $\to$ $\hat\jmath$?
Oh, cool
 
what about non conventional unit vectors?
$\hat\omegamath$
 
$dr=r\cos(\omega)\hat{i} + r \sin(\omega)\hat{j}\;dt$
 
12:52 AM
The "math" bit only gets rid of the dot on it
so it's not needed for omega
 
whats the code for an umlat
 
$\widehat{שי~הורוויץ}$
 
I think it's $n\hat{o}r\hat{m}a\hat{l}$
 
You're a unit vector
 
only one yud
 
12:54 AM
Fixed
\$\ddot a\$ $\to$ $\ddot a$ is an umlaut, I think
 
$\hat \ddot a\math$
 
$\hat{\ddot a}$
\$\hat{\ddot a}\$
 
yeah but the math gets rid of the dot.
i wanted to see an offsided single dot umlaut
 
…$a$ doesn't have a dot
\imath and \jmath are special codes
$\imath$ and $\jmath$
You can't just add "math" to everything
 
see i told you i'm bad at this latex thing
 
12:58 AM
how do i do that Latex thing again
 
$\LaTeX$
 
i can only fit so many languages and i have hebrew mathmatica and english stuck in my head no more room
 
oh
$\LaTeX$
 
Just Hebrew and English? Amateur :)
 
how many you got? i'm assuming arabic
tu hablas espano?
 
1:00 AM
Nah, Spanish
 
nailed it
 
Sí, hablo español
Sort of
I'm learning it
It's hard
 
E de português, vocês manjam? É bem mais pesado pros não latino-americanos.
 
harder then hebrew easier then english
 
1:01 AM
heh
 
nope only one country speaks that
 
Two
Well, more
but only two important ones
I'm not convinced Angola exists
 
Brazil and Portugal
@AkivaWeinberger LOL, I used to watch an Angolan novel
 
How do you "watch" a novel
 
how do you not watch a novel
 
1:03 AM
@Chinatsu-creepy-chan No idea what that means, by the way.
 
oh, I forgot novels have a different meaning in english
 
i thought thats the only way to digest it
 
Are you eating them too?!
Stop starring everything
They show up on the sideboard
I want the sideboard to be full of mathy stuff
or funny stuff
 
Well, I dunno
 
1:04 AM
too late
quick everyone say a bunch of funny or math stuff
 
Speaking of, there was a math problem you were working on…?
 
Ask me if I'm a tree. Are you a tree? No.
 
I'm watching a recorded lecture and I'm raising my hand and the guy in the video isn't calling on me :(
 
a bunch of funny or math stuff hahaha $\LaTeX$ $\int_{123123}^{123123123} 5$
 
(I should get back to that recorded lecture, actually)
 
1:06 AM
LOL
@AkivaWeinberger Oh, yeah, that one of the differential
I can't go further. Something's wrong;
31 mins ago, by Chinatsu-creepy-chan
that relation HAS to be $\vec{r} = r\cos(\omega t)*\hat{i} + r\sin(\omega t)*\hat{j}$
( $\vec{r}$ is the position vector and $r$ is the radius of the circular motion - constant. they're not the same)
 
\$\cdot\$ $\to$ $\cdot$ for the product, by the way
@Chinatsu-creepy-chan Yeah, makes sense, gives you a circle traced out at angular speed $\omega$ and radius $r$
Don't know if that's what you want
 
Yup, but I'm trying to find this from that differential
 
so would r⃗ =rsin(ωt)∗i^+rcos(ωt)∗j^ i'm not even going to try to render it
 
(I guess the actual speed would be $r\omega$)
 
@AkivaWeinberger scalar speed
 
1:11 AM
As opposed to the velocity vector?
 
what do you mean?
@shaihorowitz yes
24 mins ago, by Chinatsu-creepy-chan
$d\vec{r} = r\cos(\omega\,dt)\hat{i} + r\sin(\omega\,dt)\hat{j}$
 
and this r⃗ =rsin(ωt)∗i^+rcos(ωt)∗j^ is the integral of dr=rcos(omega)∗idt+rsin(w)∗jdt
 
almost what about r⃗ =rsin(ωt)∗i^-rcos(ωt)∗j^
 
it is actually $\int{r\cos(\omega\,dt)\hat{i} + r\sin(\omega\,dt)\hat{j}} = r\cos(\omega t)\hat{i} + r\sin(\omega t)\hat{j}$
starred? why
 
1:17 AM
its mathy and you found the right answer
 
Interesting notation that came up in that lecture: $\displaystyle\underbrace{V\otimes V\otimes\dotsb\otimes V}_{d~V\rm s}$ got written as $V^{\otimes d}$
 
interesting
makes sense i guess
 
@shaihorowitz nope, I mean that HAS to be the solution. I want a proof that I can do that
 
oh well its still mathy and its good to have in the sidebar as our goal
 
1:19 AM
It's like an exponent, but you have to specify exactly what type of "product" you're using 'cause $\otimes$ and $\times$ are different in the context
and $V^d$ would mean the thing with $\times$
 
I always get differential inside trig funcs in my physics proofs
 
you can also define it as addition and you'd get multiplication.
 
I need to know how to integrate that
 
i thing my favorite thing to define it as is ^ @AkivaWeinberger to get hyperexonetials we have from this + to * to ^ to up arrow to onwards
 
1:21 AM
the mind that alters alters all
I always thought this was the quote
 
@ForeverMozart Say what?
 
but actually it is "for the eye altering, alters all"
 
I have never heard of either of those. What's it mean?
 
@AkivaWeinberger oh its just something I think about a lot
because sometimes your past mathematical experience greatly affects how you work on new problems
 
because sometimes your past x experience greatly affects how you work on new problems
tautology
 
1:25 AM
yes but I think it can be very specific
 
DAMN. I GOT THE GEOMETRY WRONG.
 
Yeah. A lot of the time, stuff is less a product of "genius" than "I've seen similar stuff before so I know what to do here"
so you draw on past work a lot
 
like if you spent 2 years working with a particular technique, what are you going to do when confronted with a new problem? you will try to apply that technique even if it cannot possibly work
yes it can be useful, but it can also lead you astray
 
i dont think its so easily to separate the causes and effects to how we get learn
 
"When all you've got is a hammer, everything looks like a nail" or something like that @ForeverMozart
 
1:26 AM
which is I think what the quote is about
@AkivaWeinberger yes that's basically the same thing
 
that i'd agree with
"When all you've got is a hammer, everything looks like a nail"
 
Proof I wanted. So I was not wrong at all.
 
but sometimes the inspiration particle of insight on math problems comes from random non math places.
 
That hammer-nail quote would probably be why I'm watching a video about Hopf algebras. No idea how they're used (and only a vague idea of what they are), but it's good to have another tool under my belt
Well, no, the reason I started watching it was that I was bored :P
and I felt cohomology was too hard
 
none of that is in my toolbelt
I took a lot of topology, but never algebraic
 
1:31 AM
Homology was really hard, but eventually it started to click
Cohomology is really hard, but… .
 
I really don't want to write my dissertation. working on new problems would be much more fun
 
find a point with ration distancces from the corners of a right triangle with legs 1 and 1
^ not on the triangle
 
its a fun hard but solvable problem
finding a point on the inside of the triangle is conjectured impossible
 
a rational point is a point in the plane with both coordinates rational?
 
1:38 AM
sorry i meant rational distances
 
Rational distances to each of the three vertices?
 
so a point with rational distances from all three corners?
 
"Conjectured impossible"? So an open problem?
 
that should not be impossible
 
1:39 AM
see rational distance problem for related papers
infinite points on outside of triangle are found and paremetrized
 
how good are you at physics?
 
lol
i'd not rate myself
 
@shaihorowitz i guess its not that easy
my idea is to work with rational circles around the three points
 
@ForeverMozart i never said it was easy, i said it was hard. and yeah but solving the three Diophantine equations generated by that method is nontrivial.
 
1:50 AM
dammit. I still don't know what to do.
 
@Chinatsu-creepy-chan I ended up posting on the physics stack exchange instead
 
@shaihorowitz what the heck LOL
 
@Chinatsu-creepy-chan I have been pondering it for so long
What no upvote? just kidding
why is Rarely if ever expressible as a ratio of integers. in the chat description
 
@shaihorowitz well I proved where the point can NOT be :)
there is no point on the diagonal line through the right angle corner that has rational distance from all three
now I just have infinitely many other lines to consider
 
well your one step closer
 
2:04 AM
yeah I tried the easiest thing and it doesnt work
 
@ForeverMozart mathworld.wolfram.com/RationalDistanceProblem.html For when you want the answer. If you find a different answer however it may be your dissertation
 
does a solution always exist along a particular line?
is that known?
 
It exist on a closed curve
For the triangle that is .from the unit square its known that it cant exist on the diagonals or the side of the square. its also known that if there exist a point there exist 8 points due to symmetries and if a point exist its a rational point in the traditional sense. little else is known
 
Can someone explain to me what Euler's formula used for? Or is it just a random relationship between e^ix and trig functions (complete newb here only took lower division math)
 
used everywhere in complex analysis
very useful
also e^ipi = -1 is my favorite proof that pi is trance-dental a very hard property to prove.
you can use it to answer such question as what is i^i for example
 
2:13 AM
Like what can i write about it if i don't know complex analysis other can it's used in complex analysis? Any dumbed down version of what I could put that everyone would understand?
 
$z = \rho e^{\theta i}$ for all complex z
 
Because all I see is a relationship and nothing more. And it means nothing to me
 
did someone get anything from that differential?
any relation... anything that makes it right
 
i=cos(x)+isin(x) at x= pi/2 +2pik for k in integers. i = e^(ipi/2+2pik), i^i = e^-(pi/2+2pi*k)
please excuse my lack of latex
 
hmmm...
what if we do
 
2:17 AM
hence it answers the question what does it mean to raise something to an imaginary power
as doing so will rotate you in the imaginary plane as given by the relationship
 
$\cos(\omega dt) = \frac{d(\cos \omega t)}{dt}$
 
so i^i rotates to reals
@Chinatsu-creepy-chan Can you do that?
@notorious Did i answer your question at all?
 
Kind of. I'm still reading about it more and trying to make sense of what you wrote
So is it talking about the imaginary plane?
 
yes and no
 
complex numbers are fun and useful, even at geometry
 
2:23 AM
Can you watch a youtube video?
 
because i is in the equation in the first place its imaginary but its results are applicable in the real plane whenever one gets real values
and no unfortunetly i dont have access to volume
maybe its better stated as all real numbers are complex numbers. but not all complex are reals. so it has applications in the reals but its not limited to implications in either field
 
Can you say it like this? Every imaginary number can be writing in terms of real numbers? Idk if that makes sense
 
complex numbers are almost vectors
 
^complexes are almost vectors. and sort of complex numbers are an extension of real numbers over the reals as a field meaning that all complex numbers are of the form a+bi for a,b in reals. that being said all real numbers are complex numbers along the line b=0
 
2:30 AM
don't have 7 minutes, but skimmed it. part right part wrong
for instance (-1)^.5 is well defined and thats part of the reason it can join in
some things are not well defined like 5/0 cant join in, 0^0 cant join in, its a special case
have you taken calculus?
 
yes
Can I just say it shows the relationship between real numbers and complex numbers?
 
check out the similarities i=i i^2=-1 i^3=-i i^4=1 i^5=i, now im going to denote taking the derivative by ^* because i'm lazy
sin(x)=sin(x), sin(x)^*=cos(x), sin(x)^**=-sin(x),sin(x)^***=-cos(x),sin^****=sin(x)
its better to say it shows the relationships between complex numbers and waves.
and that the relationship is truly fundamental to i.
 
that's really weird
 
and really cool
 
yeah i guess.
 
2:42 AM
you may not be ready for this mind blowing so sit down
4^(.5) = 2,-2 in the same way (-1)^.5=i,-i. This is why a complex numbers always come in pairs, and you can do what i did above replacing (i with -i) or replace (cos(x) with sin(x)) any combinations of these will show the same pattern due to the fundamental relationship between them
i.e. if a polynomial has a root a+bi then it must also have a root a-bi
 
You can think of it this way:
$1.000001^n\approx 1+.000001n$
 
Let me butt in for a sec. Here's why the connection to cos/sin works: e^{ix} = cos(x) + i*sin(x). Differentiate both sides n times, you get i^n * e^{ix} on the left. Equate real and imaginary parts on the right, and you'll see that the alternating pattern of derivatives of cos and sin comes right from the pattern of the powers of i. Although it's more fun to think of this stuff in geometric terms...
 
For example, 1.000001^5 = 1.000005000010…
 
Please do i don't always explain things the best.
 
So we have $1.000001^5\approx 1.000005$
So, what should $1.000001^i$ be (approximately)?
 
2:50 AM
How do you take a derivative of i? I don't think I ever learned that in calculus
 
A good choice would be $1.000001^i\approx 1+.000001i$, and this turns out to be correct
 
is it just treated as a constant? (sorry stupid question)
 
yeah its a constant
no stupid questions.
no that is not a challenge but a statement of openness
 
So, what I wrote is essentially equivalent to $e^{i\theta}=\cos\theta+i\sin\theta$
because…
 
Exactly. Conveniently, most of the rules you learned for differentiating real functions still apply for differentiating complex functions. Just treat a complex constant (like $i$ or $3i + 4$) as a constant.
 
2:52 AM
$1.000001^{1000000}\approx e$, because of $e=\lim(1+1/n)^n$ (plug in $n=$ a million).
So, raising what I wrote to the millionth power, on the left, we get $e^i$
 
They are numbers, that are constant.
 
(approximately)
 
there just not real numbers
 
and on the right, through some trickery and de Moivre, we get $\cos1+i\sin1$
and this is pretty much Euler's formula
(It's cause $1+.000001i\approx\cos(.000001)+i\sin(.000001)$, and then de Moivre)
@notorious Did you get all that?
 
in truth i never truly understood complex numbers until first semester abstract algebra. This class will show you more of the fundamentals about the complex field and its behavior. and answer just what are these field things anyway
 
2:56 AM
And raising $e^i=\cos1+i\sin1$ to the $\theta$th power gives us Euler's formula exactly
again 'cause of de Moivre
 
Tristan Needham's text, Visual Complex Analysis, is really nice for building intuition too.
 
3:08 AM
\hat {יעקב}
still cant do it
i'm bad at latex and was joking with akiva earlier who put my name under a hat as you can see on the right
$\hat {יעקב}$
Yes!
 
\widehat does a wide hat
Who's Yaakov? @shaihorowitz
 
is divisibility only defined for integers? that is, is $5$ divisible by $2.5$ for example?
 
divisibility depends on which number system you're working with. In R or Q, yes 2.5 divides 5, but in Z one cannot speak of 2.5.
algebraic number theorists would work with other number systems in between Z and the ring of all algebraic integers.
 
what about that question
 
3:22 AM
what do you think?
 
i think it means integers
oh sorry right
 
@YakovShklarov Oh, sorry! I was gone for a while, and when I came back I only looked at the last comment
 
if it were Q, anything nonzero would divide anything else, making the problem trivial: every positive integer y would be a solution
 
but i think it would be an interesting extension of this problem to allow $y$ to not be an integer
 
Well, for rationals or even reals, it still makes sense to define "a is divisible by b" as "a/b is an integer"
rather than the uninteresting "a/b is a rational (or real if we're working with R)"
 
3:26 AM
but still, the answer to the question i posted would be the same even if $y$ was not an integer?
 
I don't know what the answer to that question is even without allowing $y$ to be any real
 
@AkivaWeinberger You mean to the question I posted?
 
The image thing? Yeah
 
$y = k[a_0,a_0+a_1,\ldots,a_0+a_n]+a_0$
 
What's that bracket mean? Least common multiple?
 
3:29 AM
see
if it were Q, anything nonzero would divide anything else, making the problem trivial: every positive number y would be a solution
@user19405892 @anon
 
You quoted that word-for-word
 
not in the mood for analysis :(
lol first full week here top 0.64% this week
hey @YakovShklarov where are you located?
in israel or in the states?
i'm state bound right now but my heart is in the jacob blaustien institute for dessert research in the negev
 
3:48 AM
Well I hope you can get your heart back soon
That seems important
 
they wont pay for shipping and i cant afford it on a mathematicians salary
 
Pretend you have a conference and try to get the dep't to pay for it?
Do you know where they're keeping it?
 
no but i know feynmans safe cracking method so how hard can it be
 
yeah you're fine
 
and i dont have enough senority they'd never send me
 
3:51 AM
^.O oh are you not a grad student?
 
not right now but i'm not permanetly not. I.e. i don't have my Ph.D but i'm an all but dissertation. so they allow me to be an assistant with worse pay and double the work.
still that dissertation though
 
>.> academia tho amirite
 
i don't think any one likes it besides frat boys.
 
wait, so does that mean you like expired your time as a student? How are you ABD but not a student?
You don't have to answer that if you don't want.
 
I'm just not currently enrolled in any classes or anything so i don't consider myself a student.
 
3:54 AM
Oh, I see.
 
being a student is a label that i would rate higher than teacher so i reserve its use
 
@shaihorowitz I'm in Vancouver, Canada. I did live in Israel for a few years when I was a little kid though.
 
hey mr combinatorics @EricStucky how would i go about proving that in the long term f(x) = (3x+1)/2 if x odd x/2 if even, repeat until x=1. How would one go about proving that in the long term both steps are equally likely
 

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