« first day (1599 days earlier)      last day (3416 days later) » 

Huy
11:00 PM
@TedShifrin: I only know how linear algebra was taught in my case, and I don't really know whether you would think it was not enough integrated with analysis. so maybe an example where you personally integrate it or would integrate it more?
 
r9m
@Chris'ssis How will I see it ? :D
 
I created a course and textbook, @Huy, that does linear algebra and multivariable calculus/analysis interwoven. Most students in the US learn multivariable calculus with no linear algebra involved at all. There are a few books that have done this integrated treatment: Williamson/Crowell/Trotter, Hubbard/Hubbard ...
 
@r9m First I need to receive some feedback from some professors. However I'd make an exception for TedShifrin and send it (somehow) to him to see it.
 
Huy
@TedShifrin: I assume the textbook is not freely available online?
 
r9m
@Chris'ssis ah okay ! :)
 
11:02 PM
LOL, it's not supposed to be, @Huy, but Alec Teal knows how to download an illegal free copy.
 
Huy
ic
is the ToC available for free?
 
I wish people still used libraries :P
 
Huy
the library is closed at midnight, in Switzerland, unfortunately
 
@Huy I bet you can wait until tomorrow :)
 
LOL, well, it's not like you need to see it right this instant. I doubt that the book would be there, anyhow.
 
Huy
11:03 PM
it is closed on Sundays, @MikeMiller. :D
 
@TedShifrin 4/5 of the books in my backpack are from the library... but our library is pretty big
 
ROFL
Yeah, @Mike ... students these days don't use libraries enough — they expect everything for free on pdf download.
 
Huy
Linear algebra : a geometric approach
Theodore Shifrin; Malcolm R. Adams, Mathematiker, 1956-
2011
@TedShifrin
 
Can you explain to me how we get the sum at math.stackexchange.com/questions/1076052/… ??
 
No, @Huy, wrong book :P
I'll see if I can give you a table of contents.
 
Huy
11:04 PM
@TedShifrin: It is taken until 8th of Jan anyways
 
@TedShifrin Is there a way to send my proof to you?
 
Huy
Multivariable mathematics : linear algebra, multivariable calculus, and manifolds
@TedShifrin
 
Speaking of geometric approach in linear algebra: what is a geometric reason that Dimension of image of a skew symmetric map is even?
 
Yes, @Huy.
@Huy: I'll post a TOC for you here.
 
Well... what's, geometrically, a skew-symmetric map?
 
Huy
11:05 PM
@TedShifrin: That book is indeed available twice at my uni. :D
 
@MikeMiller A thing that maps every vector to something orthogonal to itself.
 
Here you go, @Huy.
 
Huy
ty, @TedShifrin
 
With apologies to the room.
 
@TedShifrin You could edit into [contents](url) format.
 
11:07 PM
So you get a bunch of two-dimensional invariant subspaces @Behaviour :)
@Behaviour: There is no url.
 
There is one now, because you uploaded: i.stack.imgur.com/J0JBL.png
 
Huy
@TedShifrin: Do you introduce the determinant in R^3 first as the triple product or do you go straight to R^n?
 
Thanks for the lesson, @Behaviour and @Mike.
 
You messed up the URL, though
 
first in $\Bbb R^2$ and $\Bbb R^3$; general case is 6 chapters later.
 
11:09 PM
Dropped a g at the end
 
Well, I can no longer edit it. GRR.
 
Huy
@TedShifrin: I'm planning to introduce it as the triple product to my high schoolers, too. Not sure what I will do about R^n yet.
 
Should I just delete it?
 
Can't do that either, @Ted.
 
Why not?
@Huy already has it, I presume.
 
11:10 PM
You can only edit in chat iff you can delete.
 
Huy
yes, I do
 
@Huy Table of contents of an excellent book by Ted Shifrin.
 
Oh crap.
NO, please do not.
Are you doing your nonsense from the other day, @Behaviour?
 
That's the first time I've ever seen you use an emoticon, @Behaviour.
And now you've removed the evidence.
 
I am trying to think about the hopf fibration
 
11:11 PM
LOL @Mike
 
I used them often in the Tavern, not so much here. Math is deadly serious.
 
and i think hopf messed up. there just can't be any such map.
 
We're all quite deadly.
 
@TedShifrin What nonsense?
 
11:11 PM
You know quite well, @Behaviour :P
 
@Behaviour He's referring to when you complimented the one user on their use of the site.
 
The "saying nice to everyone at once" @Behaviour
 
Can't remember which.
 
@MikeMiller I want to know about the hopf map.
 
@MikeMiller "users/current"
 
11:12 PM
@Huy: I'm rather surprised that your library has two copies. However, I know that the text has been used for courses in Britain and elsewhere in Europe.
 
Well, that was a one-off joke
 
Huy
@TedShifrin: How do you motivate the dot product, and how do you define it? as a tool to measure angles?
 
Hey. You ignoring me, @Mike?
 
Huy
@TedShifrin: Our library is very, very large.
 
You should appreciate that, seriously, @Huy.
 
Huy
11:13 PM
@TedShifrin: I do. I use it on a regular basis.
@TedShifrin: E.g. I got some books on Game theory. :P
 
I start with two perpendicular vectors in $\Bbb R^2$, and use similar triangles to deduce that $x_1x_2+y_1y_2=0$. Thence motivating the dot product in general.
LOL, sorry about sticking you with game theory, but I think you'll love it ...
I'll take your course :P
 
@Ted We have your abstract algebra book and "Geometry and topology: manifolds, varieties, and knots"
 
snif I guess you are.
 
@DanielFischer I wrote a program: http://pastebin.com/TJ9Niwj9
but it doesn't work correcly.. Have I done something wrong?
 
The latter is a research monograph (McCrory and I edited it), @Mike.
 
11:14 PM
That's why I didn't call it yours :)
 
@Mike
 
@evinda In what way doesn't it work correctly?
 
duly noted, @Mike
 
Huy
@TedShifrin: I will start showing my high schoolers how a system of linear eqs can be written with matrices and vectors and then the scalar product (which they don't know yet) is just the product of two vectors. then I was going to prove that this has the property of being related to the angle between the two vectors. do you think that is pedagogically bad?
 
Eh. I guess I should stop coming at chat altogether if everyone has decided to ignore me.
 
11:16 PM
while ((i<m)&&(B[i]<0)){
       i=position+1;
}
 
I get this:
Give dimension:
9
Give y:
11

It just terminates but it should print the values of A[0],A[2]... :/ @DanielFischer
 
@evinda The above is wrong.
 
I usually start with geometry and save linear equations, @Huy, but that's my bias.
 
@BalarkaSen Only Ted right?
 
Mike too, it seems.
 
Huy
11:17 PM
I'm not a fan of geometry, and most of my teacher colleagues are, so I'm always having trouble preparing new subjects :D
 
@JasperLoy are you there?
 
@evinda I don't know what you want to do there, but that doesn't make much sense.
 
@BalarkaSen Well, it's just 2 of them. There's still me.
@Chris'ssis I am always here for you.
 
You need to change your attitude @BalarkaSen
 
@JasperLoy I wanna send you something and then, if you want, tell a few words here but the way what I sent you looked like.
(let me prepare it)
 
11:19 PM
What I say is nowhere near offensive @skullpatrol, compared to the rest of the users here. If I say "<some branch of math> is BS" why should it deserve an ignore?
 
@Chris'ssis Sure, you can always email me. Hopefully tell me your name too. I really hope to know.
 
@Chris'ssis you missed r9m
 
@DanielFischer Oh yes, it should be like that:


position=0;
while ((i<m)&&(B[i]<0)){
i=i+1;
}
position=i;


right? With these commans I find the first positive or zero element...
 
@skullpatrol There is time for that too. :-)
 
It's really silly. I'll try coming less in this chat from now on. I feel I am not welcome.
 
11:20 PM
@BalarkaSen It should not, but people can choose to ignore you or not. It's alright. They are not your close friends or family.
 
He left, @Jasper.
 
@Chris'ssis did you see the room?
 
@BalarkaSen Well, I certainly welcome you in this chat.
 
@Studentmath: It's past your bedtime!
 
@Ted It's saturday!
Oh. It's like your sunday.
 
11:21 PM
@BalarkaSen Come on! That's not true! You annoys me sometimes terribly, but I wouldn't agree that you need to leave the chatroom. :-)
 
@DanielFischer But again I get the same result...
 
LOL, oh :) Are you observant, @Studentmath?
 
Did I come in the middle of a drama?
 
I think people need to take this chat more seriously in some ways, and less seriously in others.
 
No, @Studentmath. But I seem to be causing a lot of tension by ignoring people.
 
11:22 PM
@Ted not really - only on Yom Kipur. I don't believe, but I respect the tradition and people that believe :P
 
Not an unfair comment, @Jasper.
Me too, @Studentmath.
 
I set up a room for you @Chris'ssis and r9m
 
@skullpatrol Why? :-)
 
@skullpatrol There are no private rooms on SE.
 
@JasperLoy True.
 
11:23 PM
@evinda Your array is uninitialised.
 
So I think we should all not set up more rooms and clutter the internet with these rooms.
 
To do real math @Chris'ssis
2
 
Huy
@TedShifrin: I think I will like Game theory too, I don't blame you for it at all. I really needed enough participants for the class to form, because it increases my salary for next term by 50% and otherwise I would have to be on budget
 
@skullpatrol Thanks, I appreciate you consider real math what r9m and I do. :-)
 
We're teaching it in the spring, too, @Huy. Our most popular undergraduate offering.
I think my colleague is using an on-line text he found.
 
11:24 PM
I really wanted to take it, but wouldn't have the chance.
 
Huy
@TedShifrin: there is a lecture at my uni in spring about it too. I think I will study the book of the lecturer about Game theory, use it to prepare my course and then take the exam at uni for free
 
@Studentmath: I am furious with myself that I didn't take probability as an undergrad ... or teach it 25 years ago.
 
Huy
wasn't it compulsory? o_O
 
Cool idea, @Huy, if you really learn it :)
No way compulsory.
 
Huy
@TedShifrin: I have to really learn it. I want to be a good teacher, and I can only be if I really understand what I'm teaching.
 
11:27 PM
Absitively, @Huy. I bungled a few things in the probability course, but for the most part, I knew what I was doing :P
 
@Chris'ssis So what secret do you wish to tell me? I am waiting...
 
@JasperLoy 2 min
 
I had a long talk with Ethan over email just now. We shared some secrets.
 
@Ted I guess I will be furious with myself about many courses that I didn't take :P But at least I have probability
Speaking of which, did you encounter any interesting questions since the test?
 
BTW, @Huy, it wasn't in the book, but I ended my course this fall with a discussion of Fourier series (an extension of orthogonal projections, just working in $C^0[-\pi,\pi]$ with the $L^2$ inner product) and applications. One was Chris'ssis's obsession. The other was the Isoperimetric Inequality in differential geometry :P
LOL, no, @Studentmath, the test was interesting enough. I'm done :P
 
Huy
11:28 PM
ic
maybe, if I have some free time anytime soon, I'll have a look at the book
 
Ha at free time
 
Maybe I should send dear Lee an email asking about the progress of his book. =)
 
Huy
I really hope I can get to eigenvalues fast enough with my students. I'd hate to teach them so much about linear algebra and have to skip cool applications just due to time issues ._.
 
Haha - you do have one more semester before retiring, don't you?
 
@JasperLoy can you give me your e-mail one more time ?
 
11:30 PM
no, @Jasper, don't be a pain in the a**.
 
@Chris'ssis Yes, it is jasperloy at outlook dot com. Please tell me your name too so that I can add it to my contacts.
 
I agree, @Huy. Eigenvalues, eigenvectors and applications should come as early as possible.
 
Huy
@TedShifrin: But they are soooo sloooow :(
 
@TedShifrin I think you should just say ass instead of a**.
 
LOL @Jasper
I didn't want you to be insulted :D
 
11:31 PM
It's Lee's ass, not mine, lol.
 
Well, I don't want him to be insulted, either.
 
You should be considerate of the asses of others.
4
 
In general
 
I think Lee should try not to retire for another ten years or so. I really hope I can get him to be my advisor.
 
Anyhow, I'm off to bed - g'night!
 
11:33 PM
One never knows. Some mathematicians don't retire until 90. Others of us decide not to press on.
 
Later pal
 
@JasperLoy Look at what I sent you (check your email). There you also see why I said I might put the proof to the Basel problem in one line.
 
Night, @Studentmath :)
 
Huy
I have one thing I actually still didn't really decide. Do you think talking about the rank of a matrix is necessary for high schoolers? Another teacher thought I should skip it to get to eigenvalues faster, but I feel like it can also show quickly whether a system of lineqs has no, one or infinitely many solutions (and what dimension the solution space has)
 
@TedShifrin Should it be easy to see that an integrable almost complex structure is induced by a complex manifold?
 
11:34 PM
Rank is easy, @Huy, in terms of echelon form. Worrying about rigorous linear independence and bases and the four fundamental subspaces slows you down more. But I definitely want dot product and orthogonality as important ... which many linear algebra books postpone 'til the very bitter end.
Sure, @Mike. That's why integrability means :P
 
Huy
I do the dot product right after I talk about matrix inverse
 
I do dot product first week, @Huy :P
 
Huy
I had to do "what are vectors" during the first weeks
 
I want meaning to all the matrix stuff.
Weeks? Surely not.
 
Huy
and what are lines, and planes, and how are they represented using vectors
 
11:36 PM
The definition I know is just 'locally complex'... d'oh, nevermind
 
Huy
and they are struggling with it a lot
because, geometry.
 
Right, but geometry comes in there. What is a normal vector to a plane?
 
Huy
of course it comes in
but that's why it's taking so long
 
LOL, ok.
I'm going to cook/eat dinner. Y'all have fun.
 
Bye.
 
Huy
11:37 PM
have a nice dinner, @TedShifrin
 
@JasperLoy did you receive my e-mail?
 
@Chris'ssis Yes.
 
@JasperLoy OK
 
Can anyone advise me as to how to write this: $[ p^*_n =\binom{\text{number of partitions of }n}{\text{into an even number of parts}}-\binom{\text{number of partitions of }n}{\text{into an odd number of parts}}. ]$ as a power series representation?
 
@Chris'ssis OK, I replied, nothing much though.
 
11:41 PM
OK, I appreciate!
I'm out for now.
 
@DanielFischer I initialized the array and I got this:

Give dimension:
9
Give y:
11
Give a value for the 0 position of the array
-55
Give a value for the 1 position of the array
-13
Give a value for the 2 position of the array
-5
Give a value for the 3 position of the array
-1
Give a value for the 4 position of the array
0
Give a value for the 5 position of the array
43
Give a value for the 6 position of the array
52
Give a value for the 7 position of the array
85
Give a value for the 8 position of the array
 
I suspect there is a deeper meaning behind this:

Which is greater, $9*12$ or $10*11$? What about $100*103$ vs $101*102$?

well consider $a, b, c, d, a<b<c<d$ and all consecutive integers. then $a(a+3) = a^2+3a$ whereas $(a+1)(a+2) = a^2 + 3a + 2$, so clearly b*c is greater. **BUT ONLY BY A VALUE OF 2**.
Always by a value of 2! isn't that beautiful?
 
@DonLarynx There is a much easier solution.
 
@Jasper go on...
 
@DonLarynx Sorry, saw wrongly, lol.
@DonLarynx But the meaning is clear if you look at the algebra, no more, no less.
@DonLarynx One can also compare (x-1/2)(x+1/2) and (x-3/2)(x+3/2). Yes, that's what I sort of thought of.
 
11:56 PM
In fact this could be generalized to nonconsecutive integers, just take the first integer to be $a$, and then use $b, c, d$ in terms of $a$. e.g. $302*405 ?? 350*375$ means that you get $(a)(a+103) ?? (a+48)(a+73)$ to get $a^2 + 103a ?? a^2 + 121a + 3504$, clearly the second product is greater by $18a + 3504$. Interesting.
 
@DonLarynx It is interesting but nonetheless trivial.
2
 
I will go to bed in 2 hours.
 
@evinda We should. You have a bug in your code. One on line 39, another is that you don't watch out for ... The other one is what gets you the wrong result here. There may be more bugs, haven't looked at everything. Time for a debugging session. The good old-fashioned printf-debugging is fairly easy and tells you what's wrong. Additionally, put spaces around your operators, that makes the code much more readable. And generally, you shouldn't expect sorted input, so you should sort your array
 

« first day (1599 days earlier)      last day (3416 days later) »