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6:14 PM
@BenjaLim: do you remember why you voted to close this question?
 
Too localized does not make sense to me?
 
@robjohn I gave what I consider a likely explanation on the meta thread.
 
@MichaelGreinecker I saw that. The voting to close a good question is a bit disturbing.
The question is now tagged properly, although there is still no work shown.
 
@robjohn I was tageed correctly by MH, not the OP.
 
@MichaelGreinecker Yes, but I am thinking of the value of the question, not of who has created it. Perhaps it should have been made CW.
 
6:29 PM
@robjohn I think the ideal way is to flaf this and a moderator threatening to suspend the user when he continues to violate the norms and rules of MSE. If you look at the lowest voted questions of the OP, many of his questions were closed for not entirely fitting reasons by many people.
 
@RaymondManzoni you here?
 
@Soham: yes. So what do you want to know?
 
Hi Raymond, what is @doraemonpaul's contention?
 
@Soham: I don't know what you mean by contention but the guy downvoted Joriki (because he didn't give the general solution) and myself (it's not the first time : the guy has an easy downvote pass... ;-))
@Soham: what do you want to know else ?
 
Well looks like that. But apart from that, there are a few question:
1. Can you explain me his solution? How did he get it? 2. From the conversation between you and Joricki I understand there had been some thing about explicit and implicit function going on. Can you explain it to me
 
6:38 PM
@MichaelGreinecker I see that some of the comments here are along the same lines you brought up.
 
@Soham: He looked at Eqworld
 
e.g he came up with a gen solution but I dont see any way how the way we are solving allows us to come up with that kind of a solution
yes, there is a link there, I opened it, but there is no proof or anything
 
@Soham: I explained it in my first comment to him (I got no answer)
@Soham: yes of course he has no proof just the solution 'from the book'
 
Yes, indeed. It looked perfectly fine with me your comment i.e, but joricki disagrees right?
 
@Soham: not really! Joriki was not used to general solution like the one you proposed (and that I corrected). I think that, at the end, we were both ok.
 
6:43 PM
hello people
 
@MarianoSuárez-Alvarez Hi, Mariano! Nice to talk to you after a long time.
 
hello Mariano
 
Dear friends: I have a question. I am learning to code. I learn some useful things. How do I stock pile them on my computer (I could choose to write but I am too lazy to write after trying things out on my computer. Looking forward to your suggestions....
 
hmm... one more last request... I think I understood what joricki explained to me about the characteristics curve and the dependent variable but can you explain it again to me, I would like to cross check my understanding
 
@Soham: you may write the general solution ($\phi(a,b)=C$) or something explicit like $z=f(a)b$ (he preferred the explicit version) but in lectures the general solution is often preferred (like in your formulation)
 
6:45 PM
@KannappanSampath You want something like a wiki probably.
Or a blog.
 
@Soham: about the characteristic curve :
 
@RaymondManzoni Can we really write it as $f(a)b$? What if it is f(a)e^b
 
I have a wordpress blog hosted on my laptop where I store all the small bits of information and snippets of code that I like.
 
@JayeshBadwaik How'd I do that? :-) (Forgive my ignorance...)
 
@Soham: that was in my first comment to dorae... $a=1/x-1/y$ and $b=xy/z$
 
6:47 PM
@KannappanSampath You use linux?
 
@RaymondManzoni yes. I actually agree with your comments and the way you presented.
 
@Soham: let's detail this: we found phi(1/x-1/y,xy/z)=C
 
@JayeshBadwaik OK. I'll get back to this problem once I have linux. I am in the process of make over. Should be done by next week.
 
@RaymondManzoni yes
 
@Soham: do you want me to continue with the characteristic equation in this case ?
or detail the phi -> explicit thing ?
(I notice that I am going in both directions so choose ! :-))
 
6:49 PM
@KannappanSampath Okay.
 
@JayeshBadwaik Wonderful. Thank you, Jay. :)
 
umm... no, not really, at least not right now. I was looking for an explaination of jorickis comment to me 22hrs ago, where he explained z=f(x,y)... can you check it three big paragraph type comments addressed to me
@Soham: It's easy to get confused about partial derivatives because our notation for them is so bad. Things would be much easier if we always marked which quantities are being considered as functions of which quantities, which quantities are being varied and which are being held fixed. In the present case, you're mixing up two different things.
 
@Soham: ok the characteristic equation :
you may see it written as
 
@KannappanSampath You are welcome. There are many many solutions, you might want to try them at least some and see what floats your boat. Anyway, ask me this question again after your linux is setup, then I can tell you all the options.
 
dx/x^2=dy/y^2=dz/((x+y)z
 
6:52 PM
@JayeshBadwaik Will do! Thanks for telling me.
 
Perfetto
 
@Soham: or as : dx= x^2 dt, dy=y^2 dt, dz=(x+y)z dt
this is the parametrized version (explicit k in my comments to your previous thread)
 
ok
 
@Soham: here we have a curve (x,y,z) with a parameter t allowing evolution on the curve
 
To assist your discussion @Soham and @RaymondManzoni , gentlemen, please use chatJaX. It helps JaXify the math here just like the main.
 
6:55 PM
and not really related to your initial problem (he explained how it could be confusing to got from the initial system to this curve system)
 
yes, alright
and I understand here (x(t),y(t),z(t)) will give us the char curv
 
@KannappanSampath: perhaps that we will try this (are you ok Soham?)
 
@KannappanSampath yep, just dragging two links to bookmark toolbar is it?
 
@Soham True Dat. But why two?
 
start ChatJax and render MathJax
 
6:57 PM
@Soham Yes and enclosing the LaTeX in the delimiters $$ and similar.
 
alright.... I think we are good to go... @RaymondManzoni shall we resume?
check $f(x)$
 
@Soham Enough to use start ChatJaX I guess but it does not hurt to have it all! :-)
 
@Soham: let try it $\frac ab$
@KannappanSampath: thanks for the trick and glad to have you back !
 
okay, it works, so lets resume (thanks @KannappanSampath)
 
if just for chat
 
6:59 PM
@KannappanSampath Is it possible to study representation theory without much algebra?
 
@Soham: what do you want me to tell you more ?
 
so when I was treating xy as constant in xydz, it was wrong
precisely why? (though I have an idea but I would like to cross check it)
 
@Soham: yes $x, y, z$ had to be taken as function of a (hidden) parameter $t$ and were not independent
 
I see. okay thanks...
 
@JayeshBadwaik Well, you can pick up the rudiments by just knowing finite groups, but very strong foundation in linear algebra is desired. But, to do some nice things with characters, it is nice to have modules over group rings and algebras around, I guess. But, also, @Mariano must be in a better postion than I am to tell you what's required to be motivated enough to learn rep. theory.
 
7:02 PM
@RaymondManzoni one last thing, do you have an idea about cauchy's method of pde solution
 
you can use rep thepry as an entry point to algebra, in fact
 
@KannappanSampath Okay. My linear algebra is pretty strong I would guess.
 
you need to know what a vector space is, what a group is, and not much more really
 
@Soham: right now no but I could learn it if needed ! :-) (we all learn here, teaching is an excellent way to learn!)
 
give me a moment to pull an appropriate link
 
7:03 PM
well, that applies to rep thepry of groups; if you want to do representations of algebras, you need a little more, but starting with groups is an excellent idea
 
Lolz, we have a qual fighter. ;-)
 
@MarianoSuárez-Alvarez Okay. Are there any good introductions to it which start out in a similarly low on prerequisites way? I am already learning algebra and have finished groups and rings now and would like to have one more line of study to pursue.
@KannappanSampath Qual fighter?
 
Serre's book is great
 
the begining of Fulton and Harris' book on rep theory is also good
 
7:05 PM
@MarianoSuárez-Alvarez Seconded. I read rep. theory from there. Awesome just like his Course in Arithmetic. :)
 
@Soham : Cauchy problem I suppose (initial conditions?)
 
yep precisely
 
@MarianoSuárez-Alvarez Linear Representation of Finite Groups?
 
@Soham: what do you want me to learn transmit ?
 
7:08 PM
my question is if given a pde say $F(x,y,x,p,q)$ and a curve $C$, we try to represent $C$ parametrically and then try to find out the initial condn yes?|
then say $C := y=0,z=x^2$
 
Later. Bye folks.
 
Later.
@MarianoSuárez-Alvarez Thanks
 
so if we form a parameteric equation it is $[t,0,t^2] yes
 
Later. Bye.
 
7:51 PM
If $f(z)-z^3$ has precisely 3 roots in the unit disc $D$, does $f$ have precisely 3 roots in $D$?
 
@QualFighter not without some other conditions - for instance, $f$ could be a constant
 
Yes, i should say that $|f(z)-z^3|<1/3$ for $|z|=1$. My bad.
And $f$ is a polynomial
So i guess that condition should imply that $f$ is of degree $3$
Not exactly clear why
 
@QualFighter Have you tried using Rouche's theorem?
 
Yes. I can show that $f(z)-z^3$ has 3 zeros in the unit disc by using Rouche
oh, i got it
 
@QualFighter :)
 
7:55 PM
thanks
 
@QualFighter No problem - often just explaining the problem to someone else gives the impetus to see the solution
 
Yeah, youre right
I want to show that if $f$ is holomorphic on $\mathbb{C}$, but meromorphic on $\infty$, then $f$ is a polynomial. Given the fact that meromorphic functions on the Riemann sphere are rational, i.e. given by $g(x)/h(x)$, I want to show that $h$ is constant. Is it enough to say that if it were not constant then the roots of $h$ would be poles and therefore $f$ is not entire as supposed?
 
@QualFighter I think that would do it ...
 
thanks, i needed a sanity check
been up way too long, too much coffee :=)
 
@QualFighter we all get that problem - its been a very long time since I did complex analysis, but I believe your argument is fine
 
8:08 PM
Hmm.
 
@JonasTeuwen Hmm ?
 
I apparently said that.
 
@JonasTeuwen do you take issue with my argument?
 
I didn't read it.
 
ok...
 
8:23 PM
Spiritus Immundus.
 
Unclean spirit?
Some unwanted sediments in your rat juice?
 
Hah.
El Diablo.
 
@QualFighter one might worry that the fact you're using about meromorphic functions on the Riemann sphere might use the theorem you're trying to show.
 
@robjohn Then the theorem is certainly correct! 8-).
 
hi @robjohn. yeah, but i can prove the theorem about the Riemann sphere
piece of pie :)
 
8:32 PM
@QualFighter if you can do that without circularity, then you're good to go.
 
there would be a finite number of poles, and by considering the sum of the principle parts of the pole, you can show using Liouville that subtracting this sum from your function results in the constant function
 
Which Scotch will I feed to the Serpent?
 
Serpent?
 
White Horse Blended Scotch Whisky
 
It has to go through my esophagus, you know. So it has to be enjoyable too!
 
8:43 PM
You call your neck a serpent?
 
@QualFighter $\frac1{\sin(z)}$ has an infinite set of poles.
 
that's not meromorphic on the Riemann sphere, it has an essential singularity at infty, no?
 
@QualFighter that's correct :-)
 
there can be only finitely many isolated singularities on compact sets
 
sound of pen scribbling down the information
 
8:46 PM
@skullpatrol he's still talking about Spiritus Immundus
 
@robjohn Indeed, the deep dark inner serpent ;-)
 
jonas are you demon haunted?
 
Yeah.
 
I hate \frak fonts, I can almost never tell one character from the other.
@skullpatrol why do you want to get yourself beaten up? ;-)
Ahh, look, the spammed secretive problem solver is here.
@WillHunting Hola amigos.
 
9:02 PM
Does anyone know that related (to this) site which is for research mathematicians?
 
Yeah, there's a website based on stackexchange software which is dedicated to research mathematicians. I want to give it to my adviser, who might like it.
 
Are you talking about MathOverflow?
 
@henning maybe. i'll go check it out.
 
But it is full of...
 
9:11 PM
@Jonas ...?? (research mathematicians?)
@henning that's the site (TY).
 
@Jeff A very special kind.
 
socially awkward math nerds?
 
No.
Worse!
Algebraists of all shapes and forms.
 
algabraists! my God, man! :D
 
Yeah, I know. Scary eh?
 
9:21 PM
@JonasTeuwen but I am trying to convert myself from an analyst to an algebraist (of sorts)
 
@OldJohn That might be the right way.
 
but I only care about algebra appropriate to number theory ...
2
... unfortunately, that seems to be most of it :((((
2
 
@OldJohn Analytical number theory...? 8-).
 
@JonasTeuwen yeah - but I am most interested in Algebraic Number Theory - I must be dumb :((
 
@OldJohn Perhaps just a period of insanity?
 
9:28 PM
@JonasTeuwen then I can return to normality at some point
 
@OldJohn Yes.
 
hhh
Q4. Is it possible that degenerate Basis -solution has a basis that is unique. True or False? (about simplex -method)
Q1. Basis -matrix is not invertible if the matrix corresponds to a degerate basis -solution. T or F?
-
MY ANSWERS
Q1. False. Degecrazy means that there are more than $m-n$ negative basis -solutions where $m$ is the amount of constraints and $n$ is the amount of variables.
Q4. True. Degecrazy is not the same as the weak duality where the difference between primal and dual is not 0.

<--- I messed up here, could someone check them? (they are not fully correct)
 
Anyone lose rep to a deletion today?
 
@robjohn definitely not
 
9:41 PM
@robjohn I only lost 10 today, but this is the third or fourth time this week...
 
@anon but that is like reducing everest by a centimetre :)
 
@anon okay... I've heard of one other loss today (it missed me this time)
 
@JonasTeuwen What's so scary about algabraists?
 
they are the evil cousins of the noble algebraists.
 
@Jeff they do evil things ... like Galois cohomology ... don't go near anyone who does that
 
9:44 PM
@Jeff They secretly eat babies.
 
@anon and that's bad becaaauuse....??
 
@anon rofl
 
@old aaah. now i get it! :D
 
I happen to have a very nice pdf on cohomology. It baited me with the first section on profinite groups.
 
@jonas well, now that is actually bad :D
 
9:45 PM
Still don't know what cohomology is...
 
@Jeff That would be funnier without any ping.
2
 
@anon it's a general term for a sequence of abelian groups defined from a co-chain complex (duh!) :D
 
@anon me neither - I remember doing some homology many years ago - in Fraleigh's book on algebra - it lulled me into thinking I understood it
 
@HenningMakholm but then how would anyone know who i was talking to, then?
I got that from Wikipedia, btw.
 
@Jeff Why, the line above yours, of course.
 
9:47 PM
@henning oh. haha! yeah, it woulda been funnier :D oh well, another lost opportunity
 
do any of you guys ever get to the stage when you get so confused by all the abstract stuff that you feel like going back to an elementary text for a while just get back to feeling that you understand it all?
 
@old you mean there is another way to feel?!
 
@Jeff just wondering if I am in some way retarded
 
the other way to feel is like a god sitting in the clouds looking below at the landscape
 
@old haha. i doubt it. if you understand some of this stuff - maybe that's what makes one of us retarded! :D
 
9:56 PM
I prefer to be called a mongole, thank you very much.
 
you're welcome very much
 
haha. you guys are in rare form today. ... but i must go :(.
 
How rare.
@Jeff Bye.
 
@Jeff bye
 
If I say you're differently abled, then differently abled is what you are. None of this touchy-feely mongole stuff here, got that?
 
10:00 PM
@OldJohn I'll have some Bruichladdich.
Yes.
"specially abled".
With some very peculiar thought patterns.
 
Oh look, it's Wednesday. I think I have to go iron my dog right now.
3
 
@JonasTeuwen excellent
@JonasTeuwen I bought a new car today - and (when it arrives) plan to take it for a drive to visit some Scottish distilleries
 
@OldJohn Excellent.
@HenningMakholm Ironing dogs is an important duty. Do it with pride. Do it well.
 
hhh
@shoda What does the line `"If $i\not = B(1),...,B(m)$, then $x_i = 0$" on p.53 (Bertsimas) mean?
$i$ is scalar? And $B(1),...,B(m)$ is some vector? -No? It corresponds to the indices of the basis but what does it actually mean? What does the implication mean in practise? Cannot understand this not-equal -sign here.
i.e. I interpret this so that statements $(A)$ and $(B)$ are equivalent but probably not, they are two conditions to have a basic solution.

Does $i\not = B(1),...,B(m)$ mean $i\not = B(1)$, $i\not = B(2)$ ... and $i\not = B(m)$?
 
10:32 PM
@anon I'm Dinosaury!
 
hhh
Moved the q here.
Deleted it but are A and B equivalent? P.53 of the Bertsimas.
I think the writer did not mean so but I ask this question because I cannot see it immediately why not.
 
10:49 PM
@OldJohn Bruich -> gone. Beer -> not yet!
 
@JonasTeuwen here -> beer gone ... Jack Daniels -> maybe
 
Jack Daniels can only be used after plenty of beer.
Or as a flame accelerant.
 
@JonasTeuwen good for starting barbecues :)
 
Let $S$ be the "open unit upper half disc", that is the area defined by the joint conditions $|z|<1$ and Re$(z)>0$. I want to define a bijection of this onto the open unit disc. My idea is to map $re^{i\theta}\mapsto re^{2i\theta}$, but of course you end up missing the positive real part of the unit disc with this map. Can I fix my idea?
and the map must be analytic...
 
@OldJohn Yep.
 
10:52 PM
actually i guess it's better to map that semidisc to the upper half plane and then map it to the sphere
 
@JonasTeuwen And I'm totally Sirius on that.
 
@PeterTamaroff What.. Sirius Who?
 
@JonasTeuwen White. Black is dead.
 
@PeterTamaroff Yes you can have inequalities.
 
@JonasTeuwen You're forcing stuff. It is not fun anymore.
 
10:59 PM
I would also quit. Who would like to date a retard.
 
@JonasTeuwen =D
 
Oh well.
Forcing theory.
 
@JonasTeuwen Please, tell me more!
 
@PeterTamaroff That's more like for @Asaf.
 
@JonasTeuwen I know one can "order" $\mathbb C$, dawg.
 
11:01 PM
It makes you create really strange models for like real lines.
Everything measurable.
@PeterTamaroff I bet you do.
But can you also prove that $\mathbf C$ cannot be made into an ordered field?
 
@JonasTeuwen Define ordered field. I know what a field is, but not what an ordered field is =)
 
@PeterTamaroff A field with a total ordering compatible with the field operations.
 
hhh
-
 
@JonasTeuwen Well, I can't imagine now.
 
There a peculiar thing an ordered field must satisfy which fails for $\mathbf C$.
 
11:08 PM
@JonasTeuwen $x^2 \geq0$?
 
@PeterTamaroff It needs to have a positive cone.
 
@JonasTeuwen Tell me more =)
 
Say $F$ is our field and $P$ is our "cone" then we should have that $P$ is closed under addition and multiplications. Additionally we should have $x^2 \geqslant 0$ and $-1$ not in $P$.
So now one would say that $x \leqslant y$ if $y - x \in P$.
@PeterTamaroff No. It is what I say it is.
 
@JonasTeuwen =(
 
@PeterTamaroff Mathematicians are very environmental friendly.
 
11:11 PM
@JonasTeuwen What do you mean?
 
@JonasTeuwen Oh, I just thought it might mean something else! I catch your drift....
@JonasTeuwen HHAHAHAH
@JonasTeuwen So the "cone" in $\Bbb R$ is $\mathbb R^+$?
 
@PeterTamaroff Yes.
 
@JonasTeuwen Ok.
 
@HenryT.Horton Hey
 
11:15 PM
@BenjaLim I finally got to meet with Mariano. =)
 
Heya folks. Gotta quick question, I think i got the answer just need a lil' confirmation. Let $h:\mathbb{C}\to\mathbb{R}$ be a non-constant harmonic function. I want to show that it has a zero. My idea is to take $f=h+iv$, with $v$ the harmonic conjugate of $h$, and then argue that $f$ must be nonconstant and entire, and therefore by Picard, it would be impossible to omit the entire line Re$(f)=0$. That ok?
 
Hmm.
 
@QualFighter $h+iv$ is not a wise choice of letters!!!
4
 
Perhaps you could do.
 
:) perhaps not
 
11:17 PM
There exist holomorphic function with $h$ as its real part. Now if it is non-constant is should blow up.
Etc.
 
I want to show that $h$ has a zero
 
Yes.
 
Is my argument flawed, poor notation aside?
 
$1/h$ or whatevaaah.
Harmonic functions are solutions to $\Delta u = 0$.
Say it has no zero then the maximum should be in on the boundary of any circle... err nevermind. Beer.
 
i'm terribly confused
maybe i should just become a carpenter
 
11:20 PM
hi
working over a field K: if a matrix commutes with all invertible matrices, must it commute with every matrix?
 
@QualFighter Well, then you can marry Mary, and have a son.
 
@PeterTamaroff, is my answer right or no?
 
@QualFighter Don't know complex anal, sorry.
 
those are past events, Peter
 
@QualFighter Whuuu?
 
11:23 PM
carpentry is still an active trade
 
@PeterTamaroff excellent
 
MJD
In typed set theory like Quine's NF, or the type theory of PM, there is still only one empty set, not a separate empty set for each type, correct?
 
hhh
Trivial question: does Polyhedron need at least two contraints? I think no because 1 dim polyhedron is a trivial and there are also null polyhedrons --- used here terms polyhedron/polytope interchangeable.
 
MJD
@hhh What is a "constraint"?
 
hhh
@MJD a linear equality, inequality -- statement here such as $x=3$ or $x<0$.
Now $\bf A \bar x =\bf b$ is the polytope with more constraints. I am investigating the Bertsimas book:
http://chat.stackexchange.com/transcript/message/5953866#5953866
 
MJD
11:29 PM
Depends on if you are going to allow unbounded polyhedra.
 
I believe it is true: the argument that shows that the center of the matrix ring is the set of scalar matrices also works in proving that the center of the invertible matrices group is the set of (non null!) scalar matrices. thus, if a matrix commutes with all invertible matrices, it commutes with every matrix
bah, I don't think it is quite right as it is. What I wrote shows that if an invertible matrix commutes with all invertible matrices, then it is (non null and) scalar, and thus commutes with all matrices
I don't want that invertible :P
 
MJD
Oh, man. I tried Google search for set theories with multiple empty sets and I found the website of a crank who has set up a web site specifically to promote his version of set theory in which there are multiple empty sets.
 
@QualFighter: Yup, your argument works, methinks.
 
Thanks @FortuonPaendrag, appreciate it
 
MJD
There is also an article on set theory on Conservapedia, which I am too chicken to read.
 
11:49 PM
@FortuonPaendrag, maybe you can help me with something. I want to show that if $f$ is entire, then there is an entire function $g$ such that $e^g=f$. I'm looking at this link: math.rice.edu/~idu/Sp05/AnalysisV11.pdf, ctrl+V for "nowhere zero". I understand everything, except why the integral $h$ has parameters $z_0$ to $z$. Would you explain this, if you have a sec?
ahh, nevermind
i'm sorry
 
@QualFighter: Is there some reason it should not?
 
no, as written the solution was fine.
 
hhh
I cannot understand the point where the author makes nonbasic solution into basic and then just says that it just a definition q.
 
@QualFighter You are preparing for Quals, then? Complex analysis and anything else?
 
hhh
The paragraph below is referring to the polygon in the upper picture, p.50-51.
(Bertsimas, 1997)
 
11:53 PM
and algebra, but i'm ok with the algebra
i'm cramming for complex, i have a lot of cobwebs
 
Good luck, then! :)
 
thanks
cramming is fun
 
hhh
I cannot understand how the point $(0,0,0)$ is active with restriction $x_1+x_2+x_3\geq 1$, p51, ideas?
$0+0+0\geq 1$, makes no sense!
(not active)
 
@QualFighter: I can only Imagine. How long do you have?
 
hhh
$x_1+x_2+x_3=1$ is replaced with $x_1+x_2+x_3\leq 1$ and $x_1+x_2+x_3\geq 1$.
(only one of the constrains is active --- hey do they abuse terminolgy?! It is not a logical AND used in the book?! It only makes sense if the word "and" is "or", otherwise not)
 
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