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Chris's sis
Chris's sis
12:06 AM
I sent the solution to them.
@robjohn I didn't see you around for some time.
I need some sleep (it's late - new energy needed for tomorrow, the book is waiting for me to finish it)
 
 
1 hour later…
Owatch
Owatch
1:29 AM
Exam went badly, for everyone.
FML
I'd say I should have put 7-8 days worth of preparation, not 3-4 like I did.
Eh, maybe Im just stupid.
 
Karim Mansour
Karim Mansour
2:05 AM
@Owatch just learn from your mistakes and don't repeat them
back
@SamuelYusim what course are you taking ?
dif geo?
 
Samuel Yusim
Samuel Yusim
yep
 
Karim Mansour
Karim Mansour
if I remember correctly you study in waterloo right?
 
Samuel Yusim
Samuel Yusim
yep
 
Karim Mansour
Karim Mansour
cool
 
dermetfan
dermetfan
Hey guys! Assuming I have two (2D) convex polygons A and B, overlapping each other, how do I know the minimum displacement only on the x-axis to move A so that it doesn't overlap B anymore? Thanks, I would really appreciate some hints!
 
anon
anon
2:17 AM
@dermetfan project them down to intervals on the x-axis
 
dermetfan
dermetfan
@anon Thanks. If I'm right that would give me a distance to move them so they don't overlap anymore, but not the minimum distance.
 
anon
anon
ah, you're right
derp
 
user147690
@SamuelYusim It's fully gray now
 
user147690
Hey @TedS
 
Ted Shifrin
Ted Shifrin
Hi @anon, @AlexC, @Karim, @Samuel ... Whew
 
dermetfan
dermetfan
2:24 AM
Here's an illustration of the problem: I'm searching for MIN, not SAT min :/ sketchtoy.com/65161070
 
user147690
@dermetfan That's a pretty cool little program
 
dermetfan
dermetfan
Yeah, really useful to explain stuff if text isn't enough
 
Ted Shifrin
Ted Shifrin
Hmm, did the ignore rampage expand to include me? :D
 
user147690
@TedShifrin I don't think so, I don't think you were mentioned haha
 
Ted Shifrin
Ted Shifrin
I meant by everyone here ...
 
Clarinetist
Clarinetist
2:32 AM
ONLY FOUR DAYS LEFT IN ACTUARIAL SCIENCE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 
user147690
@Clarinetist Woooooooooo
 
Ted Shifrin
Ted Shifrin
Hi @Clarinetist and @Stan
 
Clarinetist
Clarinetist
Hi @Ted
 
user147690
@Clarinetist What do you need linear algebra for? I think I recall you said you needed to relearn it
 
Clarinetist
Clarinetist
@AlexClark Reviewing for a part-time M.S. stats program
NO MORE INSURANCE GUIDELINES!
:)
 
user147690
2:34 AM
@Clarinetist Ahhh alright, that makes sense. Do you need/know measure theory?
 
Stan Shunpike
Stan Shunpike
@TedShifrin Hey Ted!
Wow, I'm kind of a lily green today lol
 
Ted Shifrin
Ted Shifrin
How are you set to keep transmogrifying?
 
user147690
@StanShunpike Did you change your email address?
 
Clarinetist
Clarinetist
@AlexClark I can't say that I've mastered it, but I do know, for example, what a $\sigma$-field is, what a measure is and how you use the idea to rigorously develop probability definitions. I would, though, like to take a graduate-level (math-based, as opposed to "for statistics") measure theory class sometime.
 
user147690
@TedShifrin I swear these people are making it up haha. The gravatar is based on your email address running through a code
 
Stan Shunpike
Stan Shunpike
2:36 AM
@TedShifrin I'm not, I am just an anomaly. I thought everyone did that at first, but I have realized it seems to be just me.
 
user147690
@TedShifrin The code is even open source...
 
Ted Shifrin
Ted Shifrin
Interesting @AlexC
 
Stan Shunpike
Stan Shunpike
Really? That's interesting. Yeah, mine shifts every day. Periodically it gets stuck on grey
I really enjoy it :D I hate static gravatars
 
Ted Shifrin
Ted Shifrin
@Stan is speshul.
 
user147690
Stan, the only input in the code is your email address, the code is static
 
Stan Shunpike
Stan Shunpike
2:38 AM
LOL or weird. But I prefer your version
 
Clarinetist
Clarinetist
So random question
Where can I find a book on matrix algebra which covers pseudoinverses?
 
Ted Shifrin
Ted Shifrin
Strang
 
Stan Shunpike
Stan Shunpike
Gilbert?
 
Ted Shifrin
Ted Shifrin
Lots of good applications
Yup
Not good for learning proofs, however.
 
user147690
@StanShunpike For example I got this one from playing around with random email addresses: lea.verou.me/demos/gravatar.php?email=blue123456%40gmail.com
 
user147690
2:40 AM
There is a demo with my fake email^
 
Clarinetist
Clarinetist
puts in wish list
 
Ted Shifrin
Ted Shifrin
Lin Alg & Applications, @Clarinetist
 
Clarinetist
Clarinetist
Yep I found it
 
Ted Shifrin
Ted Shifrin
He has so many books ...
 
Stan Shunpike
Stan Shunpike
@AlexClark wow, that's cool. How did you learn about this?
 
Ted Shifrin
Ted Shifrin
2:42 AM
I rather like his applied math book, too. I taught a year-long course based on it about 30 years ago.
 
Clarinetist
Clarinetist
So I haven't done anything at work for the last week. Definitely wouldn't do that in academia, but dang, the business world... when you put in your two weeks, your coworkers and manager alienate you. It's strange
 
Ted Shifrin
Ted Shifrin
No wonder you didn't finish your report, Alex :)
 
user147690
@TedShifrin Hahaha this was before the report, and heyyyy I did finish it
 
user147690
@StanShunpike More interestingly, if someone makes an account and adds an image to it, like of a cat
 
user147690
And they delete there account and you guess there email
 
user147690
2:44 AM
You get their cat
 
Clarinetist
Clarinetist
I have literally spent 8 hours a day for the last week waiting for Excel to take 3-4 hours to calculate cells and save.
and then calculate this next block of cells, etc.
rinse and repeat...
I should just flood my cubicle with measure theory formulas in my last day just for the heck of it.
 
user147690
Hey @paul
 
Stan Shunpike
Stan Shunpike
@AlexClark wow, that's crazy too lol
 
Paul Plummer
Paul Plummer
Hey
 
user147690
@PaulPlummer Got a current project?
 
Stan Shunpike
Stan Shunpike
2:47 AM
@TedShifrin so you wrote a book on calc and another on differential geometry. Why those two subjects? Just because you teach them?
 
user147690
@StanShunpike That would be a weird causation :P
 
Stan Shunpike
Stan Shunpike
@AlexClark lol
 
Ted Shifrin
Ted Shifrin
And Algebra and Linear Algebra.
 
Stan Shunpike
Stan Shunpike
That's awesome. I love all those subjects.
 
Clarinetist
Clarinetist
Actuarial Science text next :P (actually, in all seriousness, you would just need a master's to publish an actuarial text...)
 
user147690
2:51 AM
@TedShifrin I love your ratemyprofessor haha, almost perfect helpfulness and almost no easiness hahaha
 
jm324354
jm324354
@AlexClark I've been watching his lectures. Wish I could take one of his classes
 
Ted Shifrin
Ted Shifrin
Well, @AlexC, that's only a tiny number of students out of over a hundred classes. But i threw out all my 34 years of evals today.
 
user147690
@TedShifrin Whaaatttt??? That's so sad to throw out
 
user147690
@TedShifrin I guess you didn't have need for them anymore but still
 
user147690
@TedShifrin Did you keep any good ones. Do any have sentimental value from good students?
 
Ted Shifrin
Ted Shifrin
2:54 AM
Much sadder getting rid of all the books and notes.
 
Clarinetist
Clarinetist
@TedShifrin Oh, I bet
 
user147690
@TedShifrin What books and notes? Why did you get rid of them?
 
Clarinetist
Clarinetist
@TedShifrin By the way, if I ever decide to get into academia... question, should I keep these TA evals from a Calc. I class I TAd for about 2 years ago?
 
Ted Shifrin
Ted Shifrin
Lots of sentimental stuff, including over an hour at my retirement thing Friday. Two former students basically broke down in tears after 5 minutes ...
 
Clarinetist
Clarinetist
Dang
 
Ted Shifrin
Ted Shifrin
2:56 AM
Scan em or a compiled version, @Clarinetist.
 
Clarinetist
Clarinetist
Thanks
 
user147690
Man it makes me sad just thinking about it haha, I dunno I don't do well with big changes and throwing out things
 
Ted Shifrin
Ted Shifrin
I probably gave away more than 400 books.
 
user147690
Wow!
 
Ted Shifrin
Ted Shifrin
Don't accumulate too much, Alex.
 
user147690
2:59 AM
I can't wait until I start TA'ing(as Americans seem to call it), I can actually start buying my textbooks then
 
user147690
@TedShifrin Yes I know, I have to counter hoard by throwing out things that I keep :\, it hurts every time
 
Karim Mansour
Karim Mansour
Hi @TedShifrin
 
Ted Shifrin
Ted Shifrin
But in the modern era you can scan stuff ...
 
Karim Mansour
Karim Mansour
alex how come you don't use your old account anymore
Hi @AlexClark btw
 
user147690
Hey @Karim . I wanted to disassociate from it since the challenge was a failure
 
Ted Shifrin
Ted Shifrin
3:00 AM
I said hi ages ago, Karim. :)
 
Karim Mansour
Karim Mansour
yeah I am just back
:D
 
user147690
The challenge had bad direction and a bad premise, and really it was just to motivate me when I did have no direction
 
Karim Mansour
Karim Mansour
oh I see
 
user147690
Yes, it is unfortunate, but now I know that projects shouldn't be planned for longer than 6 months unless it is really indepth and well planned haha
 
user147690
I'll probably plan my next few projects for 3 months or less until I get consistent
 
Paul Plummer
Paul Plummer
3:03 AM
@AlexClark Sort of, right now both of them are on a temporary hiatus. One of them was the project that I have told you and BalarkaSen, on small cancellation theory and some game stuff related to that post I did, and the other is a paper (maybe...) that I am working on with a friend.
 
user147690
@PaulPlummer Oh that's cool, the friend never comes here?
 
Clarinetist
Clarinetist
SO
I'm bored
 
Paul Plummer
Paul Plummer
Not that I know of, doesn't really do much on stack exchange @AlexClark
 
Clarinetist
Clarinetist
Anyone want a crash course in actuarial math (more interesting than the job itself, I promise)?
 
user147690
@Clarinetist No thanks haha, I am doing some ring theory
 
Karim Mansour
Karim Mansour
3:04 AM
I am doing physics
:d
solving mechanics assignment
 
Clarinetist
Clarinetist
I gotta get a new hobby. Haha. 'Been too used to my time being eaten by actuarial exams
 
user147690
@Clarinetist Find something you enjoy in math, or get an instrument or lift some weights :P
 
Clarinetist
Clarinetist
Hmm
Maybe I should give Tao's Analysis a better look...
 
Karim Mansour
Karim Mansour
haha
 
user147690
@Clarinetist I find all of these things make me feel way better
 
Clarinetist
Clarinetist
3:07 AM
Sad to say I'm out of shape, but I have managed to start exercising daily for a few days now :P
 
Paul Plummer
Paul Plummer
How about you @AlexClark, any projects? Have you decided on that tropical geometry thing?
 
Karim Mansour
Karim Mansour
I run and do math and physics and some programming in C for fun :D
 
Clarinetist
Clarinetist
Hmm, I really should learn C++ too
TOO MUCH STUFF!
:P
 
user147690
@PaulPlummer I will definitely do it, but I don't know too much about it, I really need to look into it over the next few days. It will start with Eric and around 2 other people(not including me) on the 8th of June. With communication between all of us 3-4 times a week I believe
 
Karim Mansour
Karim Mansour
i learned coding when I was young like 12 I learned C,C++,x86 assembly and html :D
@Clarinetist
 
Stan Shunpike
Stan Shunpike
3:08 AM
@TedShifrin 400 books?!?
 
Clarinetist
Clarinetist
LUCKY! @KarimMansour
 
Paul Plummer
Paul Plummer
@AlexClark Cool, did you have other mathematical plans or do you think it will take most of your time
 
user147690
@KarimMansour I can't code which makes me sad, but I know I am not motivated enough to actually learn it. I.e. I wish I could do it, but I don't care enough to fix it
 
Karim Mansour
Karim Mansour
yeah but wished I also learned math when I was young too that would have been nice :D
 
user147690
@PaulPlummer Well I need to get a good understanding of the first few chapters of Armstrong and Lee's topological manifolds for algebraic topology next sem. That should eat up most of my time
 
Karim Mansour
Karim Mansour
3:09 AM
I think if you learn abstract math you can easily learn how to come @AlexClark it has same flavour
 
user147690
@KarimMansour Yeah I know, it doesn't seem like it would be hard to do, but it would take up a heap of time. Much like learning a language(which I also want to do, but without necessity it is hard to make yourself do it)
 
Paul Plummer
Paul Plummer
Is it planned that most of the stuff will be done during the meating, or you are expected to be doing stuff outside. Because that will basically make it an everyday thing, of something that is probably totally new to you, not sure how much time you will have for other things. Is this suppose to be like research or just learn tropical geometry? @AlexClark
 
user147690
@PaulPlummer Research, but with no prerequisites - Yes full time thing pretty much, but it is happening mostly outside of semester(i.e. here in between sem 1 and sem 2) so I will have the time to spare
 
user147690
@PaulPlummer Apparently it is a new field that has low hanging fruits - and it is accessable to undergraduates, which is why CRP chose it
 
Karim Mansour
Karim Mansour
tropical geometry
sounds so funny
 
Paul Plummer
Paul Plummer
3:16 AM
I guess, I sort of think you may be underestimating the time commitment though... @AlexClark
 
user147690
@KarimMansour Hahaha it sounds to nice
 
user147690
@PaulPlummer Nah I get it, but it has a finishing date, so it won't last forever
 
user147690
@PaulPlummer My ex-girlfriend(who I still live with) will be going into uni to do her testing for her thesis the entire holidays, so I will have massive amounts of time to do study
 
user147690
@PaulPlummer You changed your gravatar? I liked the old one
 
Karim Mansour
Karim Mansour
wtf
you live with your ex gf?
 
user147690
3:20 AM
@KarimMansour My very recently ex-gf yes
 
Paul Plummer
Paul Plummer
@AlexClark No I updated my email
 
Karim Mansour
Karim Mansour
oh
 
user147690
@PaulPlummer That's what I meant haha
 
user147690
@KarimMansour 20 days ago
 
Karim Mansour
Karim Mansour
oh I see makes sense
 
Paul Plummer
Paul Plummer
3:21 AM
This one is not bad, I guess the cool thing is that it I can try bunch of email accounts, now that I have my own domain name and see what I like.
 
user147690
@PaulPlummer I don't even have this attached to my email address haha
 
user147690
I have it as Blue123456@gmail.com
 
Paul Plummer
Paul Plummer
Oh did you just make it
Oh just put someones email in there
 
user147690
 
Paul Plummer
Paul Plummer
How about this one
 
user147690
3:23 AM
You can try any there(mine is in there
 
user147690
One suspicion I have is that MSE renders them case sensitive and that website doesn't(which is weird since emails are not case sensitive)
 
user147690
But I can't render any of my old email addresses correctly(from old accounts)
 
user147690
I'll brb
 
Paul Plummer
Paul Plummer
Huh, it seems like you could figure out someone email from the picture, that does not seem secure (given that they say email is private )
 
user147690
@PaulPlummer Yes you could
 
Paul Plummer
Paul Plummer
3:29 AM
Although maybe it is suppose to be like a hash, hard to figure out where it came from
 
user147690
@PaulPlummer It would be very very hard though yep, but it is entirely possible
 
user147690
@PaulPlummer It's equivalent to a known plaintext-ciphertext attack
 
Paul Plummer
Paul Plummer
I guess one could get a database popular emails, put them in and collect the pictures then start comparing
 
user147690
Well with that you can literally try any plaintext and see the corresponding output and with sufficient cryptanalysis you could work out how it works(but worse still the code is opensource)
 
user147690
@PaulPlummer Ahhh you are right it is hashed, so only some of the information is used, so nvm
 
user147690
3:48 AM
@PaulPlummer Are you working on adding commenting on your website?
 
user147690
@PaulP Why do they constantly say $x$ in the ring, or $y$ is an element of the ring now, is there some problem with saying $x\in R$, $y\in R$ now?
 
Paul Plummer
Paul Plummer
4:05 AM
@AlexClark Did you want to comment on the site? That gravatar thing does not seem to be accurate
@AlexClark Who is they? And there is no difference
Some people do different styles, like some books never use $\in$ and some almost always use it
I have tried like 4 different emails that have cool gravatars and I get shown something else on stackexchange, maybe they modified the code or something
Is there a particular commenting system you wanted? I was thinking I would try to set up something so that comments get emailed to me, and the I would approve and it would update, or just use already made systems, like google comments or disqus, but not sure if comments are really needed
And why would you want comments? It seems like for the most part math blogs do not get many comments, and half the time it seems like correction, so email seems good enough for that
 
user147690
@PaulPlummer I think people won't give you corrections if they have to go to that much effort. I don't have any particular reason to believe this, but it just seems like very little effort to drop a comment
 
user147690
Also take Mike's blog for example, he got a comment very soon after posting, and it added plenty of information
 
user147690
 
Paul Plummer
Paul Plummer
From someone he knows...
and could just talk to
 
user147690
Oh how do you know that? Is Hard arithmetic someone he has talked about?
 
Remember me
Remember me
4:13 AM
Hello@PaulPlummer@alexC
 
user147690
@PaulPlummer Are you so sure? Their blog rolls aren't mutual?
 
Paul Plummer
Paul Plummer
I thought it was from the other Alex @AlexClark
 
Remember me
Remember me
@alexC when is your birthday? It was in may i just cant remeber the date
 
user147690
@Rememberme It was 7 days ago
 
Remember me
Remember me
Sorry i forgot
Happy belated birthday @AlexC
 
user147690
4:15 AM
@Rememberme Haha that's alright, I can legally drink in America now(although Aus is 18)
 
user147690
@PaulPlummer What other alex? The one on here with the animal picture? If you click the commenters name it goes to hard arithmetic.com and that website doesn't have mike in the blog roll
 
Remember me
Remember me
 
Paul Plummer
Paul Plummer
Oh the other other alex, which I thought I saw here once
Alex Youcis
 
user147690
@PaulPlummer AlexWertheim?
 
user147690
 
user147690
4:17 AM
Last seen 165 days ago
 
user147690
He is at berkley
 
user147690
So different uni's so it still counts as an example
 
Paul Plummer
Paul Plummer
Okay, maybe I will find a good commenting system
 
user147690
@Paul I like your current picture. I'll brb
 
Paul Plummer
Paul Plummer
It was suppose to be something way cooler....
but the gravatar thing misinformed me
 
Mike Miller
Mike Miller
4:19 AM
Yes, I could just talk to Alex. But it's reasonable to comment on someone's blog so that others get something out of the conversation.
 
Paul Plummer
Paul Plummer
True
So what would your comment have been the post? @AlexClark
 
user147690
@PaulPlummer Oh nothing yet haha, but when I am reading posts I usually do check the comments. They often complement the post
 
Brady Sullivan
Brady Sullivan
Hey guys, I'm looking at this answer, math.stackexchange.com/questions/225942/… and am wondering how to show |ab| is not always finite only knowing |a| and |b| are finite (ie. not knowing if G is abelian)
 
Paul Plummer
Paul Plummer
You would give an example
 
Brady Sullivan
Brady Sullivan
I can't think of one though, do you know of one?
 
Paul Plummer
Paul Plummer
4:30 AM
I know of a few :)
Do you know anything about presentations of groups (like $\langla a, b \mid a^2,b^2 \rangle$)
 
Brady Sullivan
Brady Sullivan
I'm not sure what you mean.
 
Paul Plummer
Paul Plummer
I think the classic example come from matrices though
 
Brady Sullivan
Brady Sullivan
If I could see that latex actually rendered I probably would understand.
:P
 
user147690
@BradySullivan Go to the star board and click the latex in chat thing
 
user147690
E.g. go here for latex in chat: math.ucla.edu/~robjohn/math/mathjax.html
 
Brady Sullivan
Brady Sullivan
4:35 AM
@AlexClark gracias.
 
user147690
A zero-divisor in some commutative ring is $x\in R$ such that $ax=0$ for some $a\in R$. So then multiplying a zero-divisor by any other element in $R$ should still be a zero divisor, i.e. $rax=r\cdot0$ means in a commutative ring $arx=0$ so $rx$ is still a zero divisor for any $r\in R$
 
user147690
@PaulP Does that sound right?
 
Brady Sullivan
Brady Sullivan
@PaulPlummer could you expand on the matrix example?
 
Paul Plummer
Paul Plummer
Sounds right @AlexClark
 
user147690
@PaulPlummer Sweet, I am getting the hang of this
 
Paul Plummer
Paul Plummer
4:40 AM
Try calculating $\begin{pmatrix} 0 & -1 \\ 1 & 0 \end{pmatrix}$ and $\begin{pmatrix} 0 & 1 \\ -1 & -1 \end{pmatrix}$
and the product
@BradySullivan
 
user147690
@PaulPlummer An element of a commutative ring is nilpotent iff it is a zero divisor, correct?
 
Mike Miller
Mike Miller
$\Bbb Z/6\Bbb Z$
 
user147690
Wait of course
 
user147690
Is that to me @MikeM?
 
Mike Miller
Mike Miller
yes
there are no nilpotents in that ring
 
user147690
4:51 AM
@MikeMiller How is that a counter example sorry?
 
Paul Plummer
Paul Plummer
Because none of the elements are nilpotent, but there are zero divisors
 
user147690
Oh crap
 
user147690
So nilpotent implies zero divisor ok
 
user147690
(But zero divisor doesn't imply nilpotent)
 
user147690
That is correct atleast right?
 
Mike Miller
Mike Miller
4:53 AM
yes
 
user147690
Since $x^m =0$ implies $ax=0$ when $a=x^{m-1}$
 
user147690
Good
 
user147690
@MikeMiller So zero-divisors form an ideal in a commutative ring
 
Paul Plummer
Paul Plummer
@BradySullivan Another example is to consider the functions $r,s:\mathbb R \to \mathbb R$, $r:x \mapsto -x$ and $s: x \mapsto 2-x$ (which can both be seen as reflections of the real line), then you calculate (rs)^n, which you can show is not the identity since you can just plug in points
(this is actually called the infinite dihedral group and is isomorphic to $\langle a,b \mid a^2, b^2 \rangle$ )
 
Mike Miller
Mike Miller
no they don't. nilpotents do
 
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