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00:00 - 13:0013:00 - 00:00

12:00 AM
@Shahar bump ?!
 
then 1/0 * 0 = 0?
 
@Nico bumped your question
Okay not always
ugh
why are you working with undefined functions anyhow?
They aren't even defined
 
it is in my book
 
Then the answer is no answer
it's undefined as well
 
@Shahar I don't understand what did you mean by bump here..
 
12:01 AM
@Graduate STAHP
 
@Nico I don't know
ANYWAY ENOUGH WITH UNDEFINED LET'S DO A RIDDLE
5 # 2 = 11; 2 # 4 = 14; 3 # 2 = 7; 4 # 5 = 30; What is 8 # 4.
This is important
 
two
 
why?
 
How did you get that?
 
12:10 AM
Hi @Mike @Karl @Pedro
 
@TedShifrin hi!
 
Hi @TedShifrin
 
Hi @Ted
@Pedro: What was that strange group you told me about today called again?
 
@Shahar i defined an operator $#: \Bbb Z \times \Bbb Z \rightarrow \Bbb Z$
 
S[something]berg
 
12:12 AM
heisenberg
 
not heisenberg
 
Heya @Fernando
 
@FernandoMartin Steinberg. =D
 
Thanks!
 
$\Bbb Z \times \Bbb Z \rightarrow \Bbb Z$?
What do you mean by that?
 
12:14 AM
a map from the cartesian product of the integers and themselves, to the integers
 
dang I hate this Fios Internet
@Mike I don't know what that means, what do I google?
 
@Shahar It means a map from pairs of integers to integers. $+$ is such a function.
$+(3,6)=9$ is usually written as $3+6=9$
 
Hi @robjohn
 
@TedShifrin how are things?
 
Great, thanks, and you?
 
12:23 AM
@TedShifrin slow. I have spent too long thinking about an example. I posted it, but I still think it is not as clear as it might be.
 
Example of whom?
 
But in this case, for example, 5 # 2 = 11. And # => $\Bbb Z \times \Bbb Z \rightarrow \Bbb Z$. Still not sure why.
 
it was effecively a joke
ignore it
 
oh you
so it's -5?
 
ignore that part too
 
12:26 AM
No that wasn't from you
that was from @KarlKronenfeld
5 # 2 = 11; 2 # 4 = 14; 3 # 2 = 7; 4 # 5 = 30; What is 8 # 4.
-5?
 
40 secs ago, by Mike
ignore that part too
 
okay
Wow I need to actually solve it
 
ignores everyone
 
"solve"
 
@TedShifrin Someone wanted to show a binomial equation, and wanted and inclusion-exclusion argument.
I gave two algebraic proofs and an inclusion-exclusion argument
 
12:29 AM
@Shahar Such problems provoke this kind of behavior. Esp. when it seems like the numbers are randomly chosen in the problem statement.
 
Ah ... Cool. Soon I need to start learning probability to teach it next year:)
 
They are not random
 
@TedShifrin what level of formalism?
 
@Shahar ok, what's the answer?
 
@TedShifrin teaching is a good way to learn something.
2
 
12:30 AM
Low ... Undergrad class with multivar calc as prereq
Oh, @robjohn, I'm too old not to know that :)
 
@KarlKronenfeld I don't know, that's why I'm asking
 
@robjohn @robjohn do you remember any sum involving harmonic number that yields $\displaystyle \frac{3\zeta(3)}{16}$? The idea is tha I have the feeling I met that result somewhere but I don't recollect where exactly.
 
@Shahar You seem to have a conviction the numbers were not chosen at random. I am asking for some evidence.
 
@TedShifrin sorry, it was just a comment :-)
 
I'm not disagreeing with you, @robjohn. :)
 
12:34 AM
@Chris'ssis I can look some things up, but I don't have anything off the top of my head
 
@robjohn OK. I got this result with some (multiple) integrals I study now ...
 
@KarlKronenfeld Because it was a problem presented in some TV show
 
Anyway, I have to leave for now ...
 
@Chris'ssis I will look when I get back from the park. I have someone who wants to go now :-)
 
And it was solved my people
It's apparently simple
 
12:36 AM
@robjohn OK, thanks!
 
@Shahar lol
 
PROBLEM AGAIN FOR ANYONE INTERESTED:
5 # 2 = 11; 2 # 4 = 14; 3 # 2 = 7; 4 # 5 = 30; What is 8 # 4.
 
it is an ill defined problem
i can give you any answer i want and it will be correct
 
@robjohn That result is yielded by $$ \int_0^1 \int_0^1 \frac{-x y \log(x y )}{1+(x y)^2} \ dx \ dy $$
 
@Mike Okay then here's a different question: what is the operation '#'
 
12:39 AM
That can still be pretty much anything I want
 
No, because then it won't satisfy the equations
 
sigh
 
sigh?
 
define it by cases...
e.g. mine was -5 everywhere but those specific points and whatever random numbers they chose at those points.
 
alright so let me define the problem again
IF # IS SOME MYSTERIOUS FUNCTION
AND 5 # 2 = 11, 2 # 4 = 14, 3 # 2 = 7, AND 4 # 5 = 30
WHAT IS THAT MYSTERIOUS FUNCTION~
a # b ?
 
12:45 AM
Define mysterious.
That's literally the only difference between this problem and the one you started with.
 
It's some operation
or set of operations
done to a and b in a#b
 
Oh, ok. So @Mike and I solved it. What do we win?
 
nothing because you didn't give me the function
at least the right one^^
 
Ok, I got it.
 
How do you know it's not right?
 
12:47 AM
a # b = -12a^3+123a^2-394a+406
 
Nice interpolation.
 
So 8 # 4 = -1018.
 
I was close
 
BECAUSE I GAVE YOU OTHER VALUES
This wouldn't work for 5 # 2 = 11
it won't equal 11
 
The thing I just gave you?
Yes it does.
 
12:49 AM
Who are you talking to @Shahar?
 
No it doesn't
 
No, it really does.
Check.
 
That's a regression thing though
 
So?
I gave you a function that does what you told me it does. Why is it wrong?
 
hm
let me check it
I find it hard to believe
that 8 # 4 would be -1018
lol
 
12:51 AM
so?
the point is that I can make 8 # 4 be whatever I want it to be and satisfy what you're asking
 
Yes but
IDK
 
lol
 
lol
 
ah the joy of learning how shitty these riddles are
 
This is the answer I'm going to give tomorrow
better be right
 
12:53 AM
it's right
if your teacher says it's wrong, tell them to plug it in
 
lol
It will probably be wrong
What do you get for regression with y against the value?
 
It's right, unless your teacher gave you more conditions on #.
 
No, nothing else
 
It's one of many correct answers.
 
@Shahar You can't since 2 appears twice in that coordinate
(with different results)
 
12:56 AM
Oh that's right
 
@KarlKronenfeld Karl.
 
@PedroTamaroff yo
 
Don't answer him @Karl
 
@KarlKronenfeld How trivial is it that $\mathfrak a+\mathfrak b=A\implies \mathfrak a\mathfrak b=\mathfrak a\cap\mathfrak b$? @Mike
 
@PedroTamaroff Well, it's elementary
 
12:59 AM
I said don't answer him :(
 
ah, thought you were talking about that shahar guy
 
it's for noobs
"that shahar guy"
 
we mean the other shahar guy
 
Do any of you have Fios wifi?
 
no
 
1:02 AM
It's so bad
Like
if I stood with an antenna in my hand
my Wifi would be so much better
 
See @Mike
 
@PedroTamaroff Elementary $\neq$ trivial
 
Elementary + unecessary = trivial * square root of math
 
@KarlKronenfeld Kaaaaaaaaaaaaaaaaaaaaarl.
 
@PedroTamaroff Peeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee‌​eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee‌​eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee‌​eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee‌​eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee‌​eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeedro
 
1:11 AM
That should be your avatar.
Nuff said,.
 
My avatar is the best
quick what's the charge of a proton
 
-(charge of electron)
 
number wise
 
@Shahar Some $\varepsilon$.
 
1.602 x 10^what
omg
 
1:14 AM
Small thing.
 
you guys
 
Not important.
 
1.602 x 1-^-19?
10*
 
Google it.
 
1:14 AM
coulombs
 
k
 
I like my avatar
 
mine is better @Mike
 
what is a period of a circle
 
wrong
 
1:17 AM
@Shahar Male or female?
 
is that 2*pi*r/v?
 
Because if it is male, it has none.
 
Huh?
 
@PedroTamaroff lel
 
1:17 AM
that put a smile on my face but no
period like T
 
@KarlKronenfeld Bogart?
 
What's humph?
 
$v=\frac{2 \pi r}{T}$
Right?
 
I should write my essay
 
1:19 AM
@PedroTamaroff lmgtfy
 
Hey guys--I'm not sure if this is the right place to ask, but I have a graph theory question I am having an impossible time finding an answer to. Does anyone know graph theory well? And please forgive me if this is the wrong place to ask.
 
@ricardio I have some knowledge.
 
magnetic field of the earth?
 
@Mike do you know anything about graphs of convex polyhedra?
 
nope
I mean, I know Euler's formula
but that doesn't require convexity
wait yes it does
 
1:22 AM
I know Euler's formula too omg we're like brothers
 
Ah well. I am trying to show that the graph of any convex polyhedron is 3-connected. I am pretty decent at graph theory but I have almost no feel for how a convex polyhedron behaves and I am just not sure how to proceed
 
yikes
 
wait, what's your definition of graph of polyhedron?
@Mike Related to a question by your friend, The YOLO Lifehacker.
 
@KarlKronenfeld vertices of the polyhedron + edges
 
@Mike in space?
 
1:26 AM
I don't know what you mean
 
Is the graph in space?
 
@Mike @KarlKronenfeld This is how I did it. Let $A$ be commutative, and $\mathfrak a+\mathfrak b=A$. Say $a'+b'=1$, and $x\in \mathfrak a\cap\mathfrak b$, $x=a+b$. Then note $a,b\in\mathfrak a\cap\mathfrak b$, and thus $x=1\cdot a+1\cdot b=a'a+b'a+a'b+b'b$ is in the product ideal.
 
a graph is a set of vertices and a set of pairs of vertices (edges)
 
@Mike fml
 
top lel
 
1:27 AM
@Mike A graph is a symmetric relation on a set.
 
correct but ultimately unhelpful and needlessly obfuscating
 
@Mike Just saying.
 
@PedroTamaroff Not sure why you write $x=a+b$.
 
@KarlKronenfeld Oh.
Right.
 
Just multiply $x$ by $1$ in the first place.
 
1:29 AM
=D
 
I don't understand
wait nvm
$\frac{d}{d(-14)}e^{-{14}}=e^{-14}$ omg that's fantastic
so $\frac{d}{d}e=e$
and 1+1 is also not equal to $e$
and if you divide by 2 you don't get $e$
so you take an integral
star this it's pretty cool: github.com/papers-we-love/papers-we-love
Alright I'm going to go
I have to take the square root of 01
-1*
bye
 
What is the name of the $tan(x/2)$ substitution trick in doing integrals?
 
@ThomasAndrews Weieretrass!
Also maybe stereographical...?
 
Ah, yes. I finally found the Wikipedia article.
 
1:59 AM
Hello
Nobody ever even reads my questions :(
 
I do!
 
:)
You and me must be the 2 views I've gotten then ;)
 
@PedroTamaroff:
One can have Smith normal forms over PIDs after all
I just looked it up
 
isn't that their natural domain?
 
@FernandoMartin Source?
 
2:08 AM
@Chris'ssis I have a lot of results that deal with $\zeta(3)$ such as this one, which says that $$\sum_{n=1}^\infty\frac{H_n}{n^2}=2\zeta(3)$$ I have not found any with that particular rational coefficient yet.
 
@PedroTamaroff It's used for the structure theorem of finitely generated modules over a PID.
Just like it is for fgag
 
@Pedro: Wikipedia
 
@Mike But the proof for FGAG needs that $\Bbb Z$ is Euclidean.
@FernandoMartin Let me see.
 
Wikipedia's a great source
 
I think the explanation of the algorithm is pretty bad.
 
2:15 AM
Why?
 
It kinda hard to follow.
 
yah
@PedroTamaroff It's just row and column operations.
 
@Mike Yeah, I know.
That thing makes it overly complicated.
 
2:27 AM
Holy shit. Soldier killed in Crimea.
@Mike @FernandoMartin
 
That sucks
Can't say I'm surprised though
 
2:39 AM
Wow, didn't know they had a conflict going on
Can we predict what will happen next using math? :)
 
no
 
Killed how, I'd ask.
 
@ThomasAndrews A tank fired.
@Mike Would it be correct to say a "concrete" category is a category with a faithful functor into $\bf Set$, @FernandoMartin
 
that's... the definition?
 
2:50 AM
@Mike Hungerford gives a more verbose definition.
 
Is this before he introduces functors?
 
@Mike Yeah.
 
Then that's the best way to describe it
@FernandoMartin I don't like the nLab.
 
I don't like it because it makes me feel like an idiot
But it's a great website
 
2:53 AM
It needlessly obfuscates topics in categorical language
That don't actually give better ways of thinking about them
IMO
 
<3 Hungerford.
 
Why is it called nLab?
@JessyCat Aw.
 
I have not made any progress on this essay.
Eff it.
 
@Mike Try making some progress on an esse.
 
Blues Brothers just went off. Best movie EVER! After Escape From New York.
 
2:56 AM
@Mike: It's certainly not the right place to learn about stuff
but it's cool to read about stuff you already know
which is about 0.01% of the articles
 
@PedroTamaroff An esé?
 
Not an ese! Eric Cartman made that mistake once.
Or at least the guys he hired to write his essay did.
 
@JessyCat Exactly my thought.
You're real name is Jessica?
 
Didn't we have this convo yesterday? Or was that with somebody else?
 
@JessyCat Naught me.
 
2:59 AM
It's not Jessica. I chose this name b/c of the Cheshire Cat from Alice in Wonderland.
 
@JessyCat So which is it?
 
Some people call it the Chessy Cat, and Jessy sounds like Chessy.
@Pedro, that's my little secret ;)
Nighty night!
 
Her name's Andrea.
 
 
1 hour later…
4:23 AM
@PedroTamaroff Bah, I answered something and then so did three other people.
 
 
4 hours later…
8:41 AM
So quiet in here. This afternoon, there were a lot of people in here.
 
9:14 AM
@robjohn are you here?
 
r9m
9:24 AM
@Hawk hello ..
 
@r9m hello
 
r9m
@Hawk you have any queries ?
 
@r9m meaning?
 
r9m
@Hawk anything you wanna ask ?
 
@r9m ask whom?do you mean yourself or robjohn?
 
r9m
9:29 AM
@Hawk i'm bored ...
 
@r9m Oh, I can give you a problem
 
r9m
@Hawk sure
 
@r9m $x,y \in \mathbb{R^+}$ such that $x+y=2$. Prove the inequality, $x^3y^3(x^3+y^3)\le 2$
 
r9m
@Hawk I think I have seen this before .. some olympiad question right ?
I'm not sure though ..
@Hawk $x^3y^3(x^3+y^3) = 2(xy)^3(4-3xy) \le 2(\frac{3xy + 4-3xy}{4})^4 =2$
 
@r9m I do not know about any olympiad I got it in a book.
 
9:40 AM
Are you still bored?
 
@r9m another problem
 
r9m
@skullpatrol ya man .. I got my Game Theory assignments back today ... a straight B .. simply because my proof was long and inelegant :(
@Hawk sure
 
@r9m among 7 real numbers $a_1,a_2,\ldots,a_7$, there exist two, such that $0\le \dfrac{a_i-a_j}{1+a_ia_j}\le \dfrac{1}{\sqrt 3}$
 
r9m
@Hawk PHP ..
 
@r9m If a rectangular board can be filled up by $1\times m$ and $n \times 1$ strips, then prove that this could be done with only one of the type only.
 
9:46 AM
Greetings
@robjohn Do you see a nice way to evaluate $$\sum_{k=0}^{\infty} \frac{(-1)^k}{(1+2k)^3}$$?
 
@Chris'ssis Yes, of course...
 
@robjohn without complex analysis?
 
@r9m working on the problem??
 
@Chris'ssis See this answer. I don't promise an absence of CA.
 
r9m
@Hawk yep .. on it :) Thank you
 
9:50 AM
@Chris'ssis It's $\dfrac{\pi^3}{32}$
 
@r9m Most welcome, I can give you more of it if you wish...
 
@robjohn Yeah.
@robjohn Very nice your answer there.
 
r9m
@Chris'ssis Hello ..
 
@r9m Hi
 
r9m
@Chris'ssis a few days ago you showed a really interesting series .. $\sum \sin(\pi\sqrt{n^2+1})$ .. does it converge to anything interesting ? I mean is the point of convergence known ?
 
10:00 AM
@r9m Yeah, that converges.
 
r9m
@Chris'ssis can we find a closed form for the series ?
 
@r9m see above. A closed form? I don't know ....
 
r9m
@Chris'ssis thats really nice ... I took the second approach :) .. but I was asking if we know the number it converges to
 
@r9m I don't know to answer this.
@robjohn I also have a brilliant way to prove that result.
@r9m Do you have a closed form for that? I'd be glad to see such a thing.
brb
 
r9m
10:20 AM
@Chris'ssis neither do I ..
 
10:47 AM
Guys, what's a simple notation to generate a matrix with a pattern?
(I dislike the fact that the above is the general form of a matrix)
 
@Nick $a_{ij} = f(i,j)$?
 
@Mike: ... that was what I had in mind but my programmers mentality, man. It's really bugging me out. Don't I have to first declare the matrix before I say that? Can't I do both at once.?
Something like $$A = \text{Matrix}(a_{ij} = f(i,j)) $$
 
Isn't the expression $a_{ij}=f(i,j)$ redundant if the matrix $(a_{ij})$ hasn't been defined yet?
 
@Karl: Obviously, but do you happen to know of a notation like the one I want?
 
@Nick My idea was to point out that I don't see why you want that notation..
 
11:00 AM
@Karl: Why anyone would want a notation. For convenience.
 
@Nick Any examples in mind?
 
@Karl: Nothing serious.
 
Oh, I get your point... All three of them.
 
I'm just not convinced it is more convenient in this case.
 
 
2 hours later…
12:39 PM
@robjohn I want to show you a proof that contains that result, but I bit later. I 'm working on it right now and answer a lot of phone calls (unfortunately).
 
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