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12:01 AM
@Hippalectryon Do you mind having your name placed on the list of contributors to my App?
I only know your username, so perhaps you can tell if (if you wish) later.
 
12:34 AM
hi guys
 
12:50 AM
hey @TedShifrin
I was wondering when solving apostol how much details you think I should account for when proving something
is it good to include all the details
 
It's hard for me to answer that. If I'm grading homework, I will allow you to skip details once I'm satisfied you know how to provide them.
 
for example consider this question: Determine the accumulation point of the following sets and determine if it is closed or open. 1)(a,b] For example we can see that (a,b] a is an accumulation point and I can show that explicility by constructing the ball such that when you intersect with the set it will be empty set.
not empty I meant
yeah I see
 
Some students belabor obvious points and skip details that they really din't know how to do. Obviously, that's bad.
 
yeah
I guess I could do that for a question and skip in others once I make sure I know 100 % how to do all the details
 
Right, examples like that are pretty straightforward. Not so clear when you get to harder ones.
 
12:56 AM
yeah
is the accumulation points of the following set $X = {2^{-n} + 5^{-m} m =1,2,...}$ is all of $R^1$ right ?
 
evening, chat
 
hi @Semiclassical
 
@karim @ted hi
 
btw I am at point of learning euler angles in my mechanics class
neat stuff
 
ahh, euler angles. so wonderfully awkward :)
 
1:05 AM
and relating angular velocity between PA and a fixed axis
yeah :D
 
what i do find interesting about euler angles, in retrospect, is the representation theory aspects of it
 
Say whAt, @Karim?
Hi, @Semiclassic.
 
what is the set of all accumulation point of $1/2^n + 1/5^n$
sorry
$1/2^n + 1/5^m$
 
I got the question. You should draw some pictures.
 
1:17 AM
we can easily see that $1/2^n$ will be an accumulation point for the set for any n and same thing for $1/5^m$ since we keep shifting them.
 
Well, "since we keep shifting them" isn't exactly a precise justification. Any other accumulation points? @Karim
 
also there addition should be inside
 
huh?
 
I don't know that is the points that I currently see as accumulation point I haven't written a careful argument yet just out my intuition so far
@TedShifrin
 
1:32 AM
Well, you should be able to show in one line why $2^{-n}$ and $5^{-m}$ are all accumulation points. Any others?
 
Hello Math SErs
 
heya @Clarinet.
 
Haven't seen ya in a while.
 
Just started the new job today. I'm hoping it turns out well. Was out of town for the last week.
 
1:34 AM
Ah, well, congratulations :)
 
I think the friend I have who works 80 hrs/week is an outlier (bad management).
 
or maybe just an outliar ? :D
 
I don't think so @TedShifrin ?
I was thinking
 
Haha. :P Idk, I've talked to him at 2AM a few times and he tells me he's at work
 
Maybe he doesn't go to work until 8 PM.
@Karim: Have you drawn a picture of this set of points?
 
1:36 AM
no I haven't drawn them
I will now to see how it goes
I was just thinking about it intuitively that is how I got to see that $1/2^n$ and $1/5^m$ are accumulation points
 
Well, still, you should be able to give me a one-line proof for those. But I'm still waiting to be assured that there are no other accumulation points, or, if not, to know what the others are.
 
I'll be honest, I was pretty annoyed with the naivete of the new college grads here oohing and aahing over the buildings here... but just thinking about it now, I think I'm in a good situation. I'm just itching to work and hoping these two weeks of this company bragging about itself go by quickly.
 
LOL, maybe you can find one thing to ooh and aah over, @Clarinet :)
 
Haha. Well, let's see. Free Orville Redenbacher (sp?) popcorn, juice, tea, water, coffee (not a coffee drinker here) every day
 
1:40 AM
with all that, they'd better give you a free hour in a gym, too.
 
@TedShifrin You think they'd maybe have an on-site gym with their 380 or so acres of land, but they don't!
 
Tut tut ...
 
ok so
hm
 
This place is massive
I spent most of my day in a 11,000-seat auditorium
today
 
so to be an accumulation point we have to have for every Ball B(x,r) where x is accumulation point we must have $B(x,r) \cap S \neq \phi$
where S = {$1/2^n + 1/5^m$: n,m = 1,2,...}
so
 
1:42 AM
And that's MAYBE 1/4 of one of the 10 or so buildings they have here
 
hm
1 moment thinking
 
BTW, @Karim, you should write \emptyset, not \phi.
 
What do they do with 11,000 seats, @Clarinet?
 
1:44 AM
are also some irrational numbers accumulation points ?
 
I want you to think hard and have a proof in mind before you ask me, @Karim.
 
@TedShifrin "Epic Systems Corp.’s enormous new auditorium — known as Deep Space — made its debut this week as more than 15,000 employees and customers gathered Monday for the Verona electronic health records company’s annual users’ group meeting, one of the area’s biggest tourism engines.

The Greater Madison Convention & Visitors Bureau estimates the economic impact of the annual gathering at $6.5 million, second only to the World Dairy Expo.
Deep Space, a five-story, underground auditorium, is believed to be the biggest in Wisconsin with 11,400 seats and room for a future 3,000-seat balco
 
Holy *** @Clarinet
 
@TedShifrin As I've told people sometimes, I think the CEO of this company has money to burn. Construction is being done to open 3 new buildings, and from what I learned today, construction and creation of new buildings has been done virtually constantly since 2010, at least.
She is - I think - the richest woman billionaire in the U.S.
 
1:46 AM
How many times a year do they plan to fill that auditorium? That's bigger than any sports arena I've been in.
 
@TedShifrin At least quarterly (all-employee meeting), and during the annual event mentioned above
 
All employees? How many is that?
 
@TedShifrin It's at least 8,500.
and growing
There were 760ish new hires today.
 
Wow. Maybe I should come out of retirement :P
 
But high turnover. Still, the place is growing.
 
1:50 AM
why the high turnover?
 
@Semiclassical Lots of fresh no-experience college graduates. Just google Epic Systems and you will find a slew of complaints. I've only been there for a day and haven't done any true work yet, so I don't have an opinion on the workload yet.
 
mmkay
 
@Semiclassical Perhaps I will find myself back in Minneapolis, idk. A lot of it will depend on how this job goes.
 
Well, @Clarinet, if they send you out to San Diego, come visit.
 
@TedShifrin Of course :)
 
1:53 AM
i wonder a lot about what i'll be doing post grad school
 
(I'll even give you a cooking lesson, @Clarinet ... for free. :D)
 
Lol
 
esp. since i really have no intention of staying in academia. the career outlook is just no good.
 
why
I thought post grad is actually safe
 
@Karim: You got distracted from your mission.
 
1:56 AM
0 is accumulation point 2 @TedShifrin
 
@Semiclassical Easy way to stay in academia and make $60k+: take some actuarial exams and apply for an actuarial professor position.
 
Aha. Any others?
 
no @TedShifrin
 
eh, no
i've no interest in actuarial science
 
OK, @Karim.
Nor I, @Semiclassic.
 
1:58 AM
@Semiclassical Can't blame you there, but it is an option. I'm surprised how many profs I met in my last few years asked if I could give them tips on studying for those
 
S` = {$1/2^n$} U {$1/5^m$} U {0}
@TedShifrin
correct ?
 
If I loved teaching, I would still pursue academia, even now, @Semiclassic. The job market was dismal when I finished my Ph.D.
Yes, @Karim.
 
lgood :D
 
@TedShifrin Yeah, my alma mater hasn't had merit raises since 2000, from what I've gathered
 
teaching is something i actually rather enjoyed, esp. when i got out of the intro physics grind
 
1:59 AM
Some succinct proof would be good, @Karim.
 
though i should really say TA-ing
 
I will write a careful proof now
 
Try to be short and to the point, but precise, @Karim.
 
the difference between TA-ing and lecturing is a big one, i suspect
 
1:59 AM
yeah
 
when you TA you get to play good cop bad cop :P
 
I got to do a few lectures on special topics. Loved it.
 
snerk, yep
the frustrating thing is that i actually like research in the sense of "learning things and applying them in interesting ways." and i love being part of research conversations, and lending my expertise/interest
 
Of course, often when I've taught a course using my own text, I would make snide comments about how the author really bungled the exposition and I was going to show them the right way in class. :)
 
@Semiclassical That's the part of academia I miss most of all.
I haven't seen that in industry much, tbh with you.
 
2:01 AM
Yes, @Semiclassic, I think it might be too early for you to give up altogether.
 
I remember I would spend many days and nights in the seminar room. Sure, it was hard work, but I loved it. Got to converse with a lot of the professors when they'd walk by.
 
well, @Clarinet, you hang around here a lot ... so you obviously like math.
Your $ usage sucks, @Karim :)
 
@TedShifrin Haha, very good statistical inference :P
 
yeah I know
let me fix it
 
2:03 AM
@Karim, \{ ... \} is how you do sets in math mode.
 
amusingly, i actually do enjoy grad school right now. (even if i'm still being a really stick-in-the-mud re: writing things out properly. the drawbacks of doing things a lot by intuition)
 
If anyone wants a $\LaTeX$ for dummies document, I created one for an Abstract Algebra I class years ago.
 
that would be good @Clarinetist
 
the stuff i'm doing is interesting and engaging
 
okay so we have $S = \{ 1/2^n + 1/5^m \} = \cup_{m = 1}^{m = \infty}\{1/2 + 5^{-m} ,1/4 + 5^{-m},...,1/2^n + 5^{-m},...\}$
good
 
2:06 AM
problem is, i'm enjoying it right now -precisely because- i'm not having to engage so much at the moment with the parts of it i find utterly anxiety-provoking. (and even without that i've already had a few weeks where i couldn't come into the office b/c my nerves were shot)
 
and from this we can expand it further and see that $S` = \{1/2^n\} U \{1/5^m\} U \{0\}$
 
Here you go @KarimMansour . Can't guarantee the document is free of typos (I haven't looked at it for years).
 
LOL ... no justification at all, @Karim.
 
though that's a -tad- besides the point, since in order to stay in academia at a serious research level i'd have to do a few post-docs before going for tenure
and to hell with that.
 
2:07 AM
@KarimMansour I don't explain everything, FYI. A lot of the exploring is left to you: I just give you the tools and give you explanations where I think necessary.
 
good thank you @Clarinetist
 
that's something i'm just not at all willing to explore
 
@Semiclassical Yeah, I've only heard horror stories when it comes to postdocs.
 
i'm also speaking as a theor. physics guy, and the academic job market in that realm isn't great.
 
yeah @TedShifrin I am thinking atm to make a clear proof that properly justifies it
is it supposed to be simple ?
because most of the proofs I can think of are in about many lines
to properly justify it
 
2:12 AM
You should justify why each of those points is and why there are no others. Yes, simple. I need to reboot. BRB.
 
this blog post is a good summary of why i find post-docs revolting: backreaction.blogspot.com/2015/06/…
 
@Semiclassical Yep, I read that. Huge discussion on Reddit about that
 
what about theortical physics like string theory @Semiclassical ?
 
that's not what i do myself, no
 
I mean is it safe to go there ?
 
2:14 AM
i'm more in the realm of mathematical physics + condensed matter theory. quantum stuff
 
I see
 
oh. no, i wouldn't say so.
 
Hi! Is there someone into combinatorics around here ?
 
depends on what kind of combinatorics. what do you have in mind?
 
@Semiclassical A closed form for the number of distinct unordered factorizations
9
Q: Distributing groups of objects into boxes

ilusoHow can I enumerate the number of ways of distributing distinct groups of identical objects (but various cardinality) into $k$ boxes such that at most one box is empty $(1)$ and no combination of objects is repeated between boxes ? The order of objects inside their box or the order of boxes do n...

 
2:19 AM
i've seen that before, given that my upvote for it is there
but it was beyond my capabilities
 
2:34 AM
@BalarkaSen what kind?
 
3:01 AM
hi
I was wondering if we have B(y,r) when we represent the ball as ||x - y|| < r do we consider x in our set ?
for example if our universe is $R^1$ and we consider S = (a,b) that is set of open ball in $R^1$
for example I am proving that open interval in $R^1$ is open set I want to include all the details in the proof I decided too solve stuff fully in details instead of fooling myself I know it.
so
let y $\in$ (a,b) consider B(y,r) such $r = \frac{y + b}{2}$ we can show that indeed ||x - y|| < r < b so it is less than b I can show it,but how do we know that it is bigger than a ? in order to show that it must be subset of (a,b) ?
that is how can I show for every x $\in$ B(y,r) a < ||x - y|| ?
because we could have some points ||x - y|| that is bigger than a
 
3:21 AM
@KarimMansour of course we do.
$\forall r>0\;.\; ||x-x||<r$, so, by definition . . .
@KarimMansour what's the definition of an open set?
 
all of the points are interior point
so a point is interior point if it is in our set
 
okay. that's a weird def.
anyway.
 
but how do we know it is bigger than a?
 
what are open balls in $\Bbb R$?
 
so in $R^1$ we have all points such that |x - a| < r
ohh oke
I got it
 
3:28 AM
no. open balls in $\Bbb R$ are just open intervals.
 
now construct an open interval $(a-\epsilon,a+\epsilon)$ contained in $(x,y)$ around every point $a$ in your open interval $(x,y)$. (how will you do this?)
if you can, then $(x,y)$ is automatically an open set. qed.
 
I see
yeah the way I did it is that I made sure it doesn't touch the left part b
but it could touch a
so I need to construct the open interval as you said
okay you know a way to do it is the following
 
it shouldn't touch either.
 
yeah exactly
 
3:31 AM
because if it touches $a$, it goes outside the set.
 
so?
one way is this: let $\epsilon < \min(|x-a|,|y-a|)$. done.
 
I see
 
then it touches neither, and you're done.
 
3:33 AM
one piece of advice: draw pictures.
it helps a great deal.
(tm) @Balarka, 2015. all rights reserved. :P
okay I gtg
 
yeah I am just solving questions in apostol at first I was like yes I can do this and just skip writing details but yeah that is bad because details make me think if I did it correctly or not
cya
 
r9m
@DanielFischer sama you there?
 
3:59 AM
Can't $B_3 \notin \mathscr{B}$?
It might just be a union of a bunch of basis sets, as the text says, but not one itself.
oops, wrong font.
oh, wait. ignore all this. i'm stupid.
 
 
3 hours later…
r9m
6:45 AM
@AlexanderGruber (^_^)/ hello! Haven't seen you in a while ..
 
@r9m Hi there. Yeah, I have been away. Been grad schoolin'.
How's it going round here?
 
@AlexanderGruber Hi. Long time indeed.
 
:) I haven't been to chat for some time! Mostly I mod and dip, but not tonight.
 
r9m
@AlexanderGruber :-)
@AlexanderGruber after taking up mod duties @DanielFischer has also become rarer on chat ..
 
What is a good place to obtain graphs of functions to add to answers'
?
 
6:52 AM
@r9m There is a bottomless list of stuff to get into. My site participation has gone down a lot too.
@dREaM wolfram alpha?
 
we can use those graphs?
 
@dREaM You can save them and add them to answers.
 
@AlexanderGruber So what sort of math have you been up to?
 
@TobiasKildetoft applied algebraic topology most recently.
 
@AlexanderGruber applied to what?
 
6:56 AM
data
it is getting to be a "thing" now. Gunnar Carleson has some articles
 
interesting
 
long story short, you get some data, you assume it's collected from some topological space or another, you try to figure out what the space is
people are doing stuff like trying to detect cancer with that. Finding holes in lungs.
 
@AlexanderGruber neat
 
yeah. :) How bout you? Still representin'?
 
@AlexanderGruber yeah, representing all sorts of things
put a paper on the arXiv with my mentor a few weeks ago
now I am learning about how representation theory can be used to study modular and automorphic forms (and generally the Langlands program), since I am planning to apply for a stipend for a project with a guy working on those topics
also still working on turning my dissertation into some papers
I am quite happy with how that arXiv paper turned out. The theorems are all "classical" (meaning the questions they answer could certainly have been asked 30 years ago). But the methods used are very much applications of theory developed in the past 5 years
 
7:07 AM
@TobiasKildetoft well that's very cool!
 
@AlexanderGruber and now that I looked at the references to see that I was correct about the number of years I found a really weird error. In the middle of one of the titles it says "Conjecture 2' is true"
 
@TobiasKildetoft Haha, oh my. A message from the past.
 
@AlexanderGruber Well, Conjecture 2' is from the paper, so maybe it is telling us that we are correct
 
8:12 AM
@Tobias, I was telling my mother about applied AT yesterday. It's a cool thing.
If you have, say, a 500-dimensional point cloud, you can turn it into a simplicial complex and use homology (?) to find, say, "holes" in the cloud where there's no data.
that may tell you that, for example, it's going to be stupid to invest in, say, neon-coloured dentures, because you have a "hole" in your customer data where the target audience for that would have been.
 
@Chris'ssistheartist Isn't there a repository of his work online ?
 
@SohamChowdhury But homology can only tell you something about the number of holes, not the placement (and same for topology in general)
 
8:34 AM
Well, I wouldn't know. But I suppose there must be ways of finding out interesting features of one's data.
 
@SohamChowdhury I suppose the idea is to then take subsets of the data and see if those subsets contain the holes
 
Yeah, perhaps.
Tell me, what does one do during a postdoc?
 
@SohamChowdhury research and teach (my position is formulated as "max 20% teaching")
 
Table[Limit[
Exp[MangoldtLambda[n]] DirichletL[n, 1, s] -
Exp[MangoldtLambda[n]]*Zeta[s] + Zeta[s], s -> 1], {n, 1, 42}]
 
what do you teach, @Tobias? and so the position is at a university?
 
8:40 AM
(technically, I am not a postdoc due to some strange technicalities. According to my contract, I am a researcher on a time-limited contract)
@SohamChowdhury Yes, at a university. I have not actually taught during my postdoc so far, but in the fall I will be teaching exercise sessions in linear and abstract algebra
 
What kinds of applications does representation theory have to physics and chemistry, @Tobias?
(Artin says in the preface to his Algebra, "I figured if the chemists could teach it, why not we?" :P)
 
9:01 AM
@SohamChowdhury hmm where did you read about that?
 
@SohamChowdhury The one application I am familiar with (and only barely) is that the vibration of a molecule is given by the solutions to a set of differential equations, which form a vector space. The (finite) group of symmetries of the molecule acts on these solutions, giving a representation of that group.
 
9:25 AM
@iwriteonbananas don't remember. probably reddit.
 
@SohamChowdhury There is a chapter about it in the book by James and Liebeck
 
@Hippalectryon Yeah, but I don't think he attended such stuff.
@Hippalectryon I prepared a new question to my book.
 
@Chris'ssistheartist just a little tip: use "worked with" or "solved" or "attempted" instead of "attended". :)
 
9:34 AM
@SohamChowdhury Attempted doesn't have the meaning of trying?
 
then "worked on" is best.
"attended" sounds weird.
 
@SohamChowdhury OK
 
@SohamChowdhury ;)
 
how many pages is your book now?
 
9:35 AM
@SohamChowdhury At least 500-600.
 
well . . . wow.
 
There is some work on it. :-)
 
good luck with it. and don't do the "this is obvious" thing too much ;)
 
@SohamChowdhury Thanks. :-)
 
@Chris'ssistheartist Happy Potter, but in maths :P
 
9:37 AM
@Hippalectryon loolllllllllll :-)))
 
A bit :P looks a bit awful to do though (unless you have a clever trick)
 
It's not exactly what I want, but I work on that.
Done. It was too easy.
BUT, I might add it to the very easy section.
The whole story gets reduced to calculating $$\sum _{k=0}^{\infty } (-1)^k \frac{2 k+1}{2 k^2+2 k+1}$$
I'm glad Mathematica offers latex function and I save a lot of time.
 
10:01 AM
Hello!!! :)
 
Hi :)
How are you @evinda?
 
Fine, thanks. You? @skillpatrol
 
Fine, thank you @evinda
 
$$\frac{1}{2} \pi \text{sech}\left(\frac{\pi }{2}\right)$$
 
10:27 AM
No free paper in this house anymore.
(that's amazing)
 
Hi @Hippalectryon :)
 
hi :D how's your day ?
 
@Hippalectryon I don't do anything special. What's with you?
 
Nothing special either
 
10:34 AM
What kind of music do you like to listen? @Hippalectryon
 
@evinda "movie-like" music, epic scores, ...
 
For example? @Hippalectryon
 
@evinda youtube.com/watch?v=wFJRAMzrtkc (@Chris'ssistheartist look it up too :P)
@evinda And some music from Animes also
 
@Hippalectryon niceeeeeeeee ....
 
I agree.........
@Hippalectryon Do you like this?

https://www.youtube.com/watch?v=Aoc9SrvkZHs
 
10:43 AM
@evinda They're ok, but I try to avoid lyric I understand since I usually find them very dull
Hence why I usually listen instrumental music and/or with foreint (not english/french) lyrics
 
@Hippalectryon That one was very good. It represents me. ;)
 
@Chris'ssistheartist I should make a Playlist for you some day :P
 
@Hippalectryon yyyyeaaaaaahhhhhhh!!!! :D
 
@Hippalectryon A ok... I also like this french song: https://www.youtube.com/watch?v=K5KAc5CoCuk

Do you like this greek song? https://www.youtube.com/watch?v=fsGzFSqeV98
 
@evinda Once again it's Ok, but not what I would spontaneously listen to.
 
10:50 AM
@Hippalectryon Ok...
 
@Chris'ssistheartist Btw do you also like this kind ? youtube.com/watch?v=gtmdnB95Uxc I do, but it's quite different
 
@Hippalectryon I like it too. :-)
 
ok :D
 
10:57 AM
Hi @SohamChowdhury
Do you like it?
 
hello, @evinda.
why don't they use the beautiful small Greek letters?
@evinda oh, very much. :)
 
@SohamChowdhury :)
 
remember the Lopez-Chemirani-Petrakis video I sent you?
 
Once again it's Ok, but not what I would spontaneously listen to. @Hippalectryon As do I :D
 
@SohamChowdhury Yes
 
10:58 AM
@evinda ew it's only recorded on one side, feels weird
 
I have no idea how this is a topology.
 
@Hippalectryon What do you mean?
 
the intersection of $(a,\infty)$ and $(b,\infty)$ isn't another such interval. scratches head
 
@evinda I only get the music on my right ear. One channel is empty.
 

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