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QED
12:00 AM
Some people think "n" is not a number.
but then how can n = 3?
 
To compute, $(a+b)(c+d)$ is first thought of as the product of two elements $a+b$ and $c+d$. Then we look at $a+b$ as a sum and use the distributive property to get $a(c+d)+b(c+d)$ where we are still looking at $c+d$ as an element of the group....
 
@anon Spoonwood???
territory
 
QED
@Skullpatrol you're ignoring me again
 
Next we look at $c+d$ as a sum of two elements and use the distributive property again to get $ac+ad+bc+bd$.
So we need to look at $a+b$ as an element of the group and also as the sum of two elements of the group.
 
@QED your explanation was clear, but again I'm not able to talk to two or more people at one time sir
 
12:04 AM
I don't know if that relates to what you are trying to do or not
 
QED
@Skullpatrol, will you stop ignoring me please
 
@QED I will try
but again I'm not able to talk to two or more people at one time sir
@anon Could you please elaborate on "the distinction between the result of an operation and the operation itself expressed in the same way with notation. We've officially hit Spoonwood territory here."
 
QED
I'm not asking you to
 
The distinction part or the Doug part?
 
@anon the distinction part
thanks for the link
 
12:13 AM
See here. The expression $2\times(3\times4)$ evaluates to, or results in, the number $24$, but technically it represents the process of multiplying $3$ times $4$ and then feeding that result into $2\times[]$ and getting the result of that. So on the one hand it represents a number and on the other hand it also represents the operations to get to that number.
 
@anon thanks for referring me to a post with -25 votes ... I think I'll drop the question thanks
@anon So does a + b represent a number or the operation to get that number?
 
Both.
 
and the same holds true for ab
 
Mhmm.
 
12:32 AM
@anon So when pre-algebra students are confronted with the statement "we name something in algebra simply by how it looks, such as a + b is called the sum of a and b" We should tell them that this expression, a + b, is both the adding of a and b together and the resulting sum???
 
I would tell them it can be understood in both those ways, yes. Why, are you supposed to be teaching a pre-algebra class? Or are you taking pre-algebra?
 
Both
 
Goddamnit. This is a Windows computer and there's no MSPaint on it!
 
Isn't Paint the reason people use Windows?
 
I can screencap with Ctrl+PrintScreen and it copies the image to my clipboard. How do I save this as an image using either Gimp or OpenOffice Draw?
 
12:46 AM
Often there's a "New from Clipboard" option in the File menu. Maybe just make a large new document and hit Paste?
 
You can't define a derivative directly because limits won't generally exist inside fields that are incomplete, and moreover there is an arbitrary choice of valuation necessary for the definition to make sense. So I was thinking of one possible workaround in particular (Einstein notation used):
 
Hadn't seen that one. Interesting.
 
This is some scratchwork I got on the idea.(I have 50 secs left)
bye
 
@anon Thanks for the answer
bye
;-)
 
 
2 hours later…
2:38 AM
hi
@all
 
Hi
 
2:55 AM
@QED Hi, QED I would like to apologize for ignoring your comments earlier.
@QED Would you like to pick-up where you left off?
 
3:38 AM
hi to any that's here...
 
Hi @Srivatsan.
 
I can't believe this. I slept through the whole day, and got up at 10. I mean pm. =)
 
It happens. Long night?
 
Not really, I might have slept at 2am. =) But I hadn't slept properly almost the whole of the week...
 
I think what people feared is happening. And he still can't spell Diophantine.
@Srivatsan Ah, that can catch up to you.
 
3:49 AM
@DylanMoreland With a little twist: one side is a square and the other a cube. =)
 
Yes, at first I was afraid that he was just posting the same question again.
I find it hard to balance "I'm excited at every moment to be working on my stuff" and "I am going to wind down and sleep by 11 so that I can do work three days from now".
 
Huh, Kim Jong Il is dead.
 
I saw that. I wonder if anything will change.
 
Can someone check my proof of Liouville's theorem with Riemann surfaces? Let f be a holomorphic bounded function on $\mathbb{C}$. Then using the transition map z to 1/z, we transport this function to a function defined in a neighborhood of the point at infinity (which is 0 now). It's bounded in a neighborhood of 0, so we can holomorphically extend it over 0. We now have a holomorphic function on the entire sphere, so it must be constant, because the sphere is compact.
(the last bit is by the maximum modulus principle for riemann surfaces)
 
@Potato Did you see my message from yesterday?
 
4:00 AM
I brought it up once and raising it again. Anyone interested in mentoring me?
 
Chaitin's constant looks good on you, @Zeeshan.
@ZeeshanMahmud What's mentoring mean?
 
Thank you dear sir.
 
@ZeeshanMahmud What do you mean by that, exactly?
 
Well, like a master-pupil relationship. A guide, a counselor. Someone who will work with my limits and pose problem for a day. And at the end I will give him the solution. :)
 
@ZeeshanMahmud "dear sir"!? Stop talking like iyengar, already! =)
[just kidding]
 
4:02 AM
Sorry. Touching your feet Srivatsan
 
@ZeeshanMahmud - What subjects?
 
@Srivatsan Perhaps I can start with topology/linear algebra or even number theory or combinatorics. Next semester I will take multivariable calculus so I am covered in that region.
 
This is an honest question. Don't you have books and stuff? Are you self-studying?
 
@DylanMoreland I have now. The problem involved showing that if you have a holomorphic function that had constant modulus on both boundary rings of an annulus (and the constant is the same for each ring) then the function is constant on the annulus.
 
@Potato Ohhhh. I misread, then. Did you ever figure it out?
 
4:05 AM
@DylanMoreland So your example of f(z)=z doesn't work for that. My fault for not being precise, though. By the way, does the Riemann surface proof above look good?
 
I must admit that I haven't thought about it since then. I'm surprised whenever I can do any sort of analysis.
 
@Srivatsan I am off current semester. I HAVE books, but one-to-one interaction helps. And imagine the benefit of boasting that someone was godfather of the man who will solve/solved hodge conjecture. ;)
 
@DylanMoreland Well, I'm not sure it's true. The original problem had an extra condition that made it easier.
 
@Potato Oh, what was that?
 
@DylanMoreland Well, it sounds true-ish in generality.
 
4:06 AM
@ZeeshanMahmud HAH.
:)
 
@All no I read in the self-studying threads in SE that first find a teacher...
 
@ZeeshanMahmud But you are at a university?
 
The problem was to show (without recourse to the general theorem on this kind of thing) that there was no analytic isomorphism between the annulus with boundary rings |z|=1 and |z|=2, and the one with |z|=1 and |z|=4
 
@DylanMoreland Enrolled in community college with target to transfer to UCI
 
@Potato Oh, I've done that problem. Hm.
 
4:08 AM
@DylanMoreland You don't have a PhD from Berkeley by chance?
 
Ah, nice place. Approachable too. Karl Rubin is there; he knows everything.
@Potato Hah, no.
Is this in the Berkeley prelim problems book?
 
Yes.
 
I think it's a common problem.
 
But it seems true that in general, if we have f(z) with constant modulus on both rings, it should be constant on the annulus.
Without the extra condition.
 
I know a lot of people who do have such a thing—I could ask them.
 
4:09 AM
Perhaps I can start in this chat. Perhaps a basic problem that I can solve without goolging? ;)
 
@ZeeshanMahmud Is there anyone at your community college with whom you're close? On the faculty, I mean.
 
@DylanMoreland I alreay mailed my logic teacher but since the semester is over he didn't see it or got annoyed by my nosyness. But next semester I will take his class again (Symbolic Logic)...
 
Professors are very busy, especially around this time of year.
 
@ZeeshanMahmud I don't think googling is the right way for any problem -- basic or not. If you follow a textbook, then surely every problem would've been designed so that it can be solved given only the material covered till then + the prerequisites.
 
I see...
 
4:13 AM
Zeeshan: Let a, b, c, d be four real numbers such that
a + b + c + d = 8,
ab + ac + ad + bc + bd + cd = 12. Find the greatest possible value of d.
With proof.
There is a problem for you.
 
Gotta walk the dog. Will be back in a bit to pick up on these two threads, though.
Oh no, not memes. Not here.
2
 
Really? It's frowned down upon?
 
No, I am tempted to post a lolcat picture myself.
 
@ZeeshanMahmud Best getting working on that problem if you eventually expect to crack the Hodge Conjecture. It is a long road.
 
4:17 AM
Ok I will be back. BD cricket game started.Farewell...retiring dans mes chambres.
@Potato Copied it. Will get back here..later.
 
@ZeeshanMahmud What game is this? Glad there is someone here who speaks about cricket. I like to listen even if I can't speak about it myself.
 
@Srivatsan BD vs Pakistan. Test.
Ok i am out.. :)
 
Can someone verify my Riemann Surface proof? I am working through this book alone and need validation :(
 
Can anyone teach me what filters and ultrafilters are all about? I would like some hand-holding actually...
 
@Potato: Can you state the theorem you are trying to prove?
 
4:24 AM
Liouville's theorem.
 
@Potato: Give the statement please.
 
Can someone check my proof of Liouville's theorem with Riemann surfaces? Let f be a holomorphic bounded function on $\mathbb{C}$. Then using the transition map z to 1/z, we transport this function to a function defined in a neighborhood of the point at infinity (which is 0 now). It's bounded in a neighborhood of 0, so we can holomorphically extend it over 0. We now have a holomorphic function on the entire sphere, so it must be constant, because the sphere is compact.
(the last bit is by the maximum modulus principle for riemann surfaces)
 
@Potato: I don't want to see your proof yet, I need to see the statement first.
 
A bounded holomorphic function must be a constant.
bounded on the regular complex plane
 
Then yes, your proof is correct.
Although checking that it can be holomorphically extended does require some work...
 
4:26 AM
Well it's a lemma in the book.
But yeah you're right.
 
The real meat of that proof is to show that non-constant holomorphic maps between Riemann surfaces are open.
 
The real meat of which of the proofs?
Liouville, or Riemann's on removeable singularities?
 
Hm, although you don't really need that here... nevermind.
 
Weird. I am nice to this guy, and I get strange looks from him. :-/
[That was in real life.]
 
Why is Jacob Lurie so smart?
 
4:35 AM
@Potato What textbook is this?
 
No textbook.
 
@Potato: I think it's a little too early to be reading Jacob Lurie's works...
 
As do I. But I enjoy the placement of the symbols on the page, at least.
What is higher category theory even good for?
 
I'll tell you when I find out!
 
What is category theory even good for?
 
4:39 AM
At the moment it seems to me that the subject is divided into 2-categories, which is of interest to categorists, algebraists, and computer scientists, and infinity-categories, which are of interest to geometers and homotopy theorists.
 
Besides algebraic topology.
 
As for 1-categories, they are everywhere.
 
Have they infected even analysis?
 
@Potato It looked good to me. I would have been more explicit about charts and stuff but I'm slow.
 
@DylanMoreland Thanks!
 
4:40 AM
@Potato: It involves hard numbers, then probably not. :p
 
Oh, I confess I like this answer.
 
How much mathematics should I know before tackling "Categories for the Working Mathematician", and how much will that book help me as a mathematician?
I want to read it just so I gain arcane category-theortic powers, but any actual applications would be cool too.
 
5:03 AM
I look in there if I need something.
If you can read it straight through, then perhaps you should? It might mean that you have a disposition or talent for the subject.
 
5:16 AM
@Potato: If you're going to work in hard analysis and don't intend to ever learn anything else, then probably not of much use. Even if not, I think there are gentler introductions.
 
@Srivatsan If he accepted more answers, would that make his questions and comments any less bad? :)
 
5:43 AM
@DylanMoreland Well, that's why I have stopped caring about their questions. =) // For disclaimer sake: I haven't posted any answers, so I haven't been affected yet...
 
6:07 AM
is it paranoid of me to think alias account may post simple questions to test users fundamental knowledge such as the "low hanging fruit" :)
 
@ZeeshanMahmud Dude, I couldn't parse that sentence. =)
Not sure if it's because I am slow right now...
 
@Srivatsan In the "low-hanging fruit" link, Dylan wrote that he is surprised no one has posted the answer. Makes one wonder if so many people are browsing, how come they don't post the answer(!). :)
 
I see.
What's the question btw? To solve that inequality? Or to explain setbuilder notation?
 
@Srivatsan Well he already accepted my answer, so I presume it was to solve the inequality..
 
@ZeeshanMahmud Um, I texed your answer.
 
6:15 AM
Thanks. Now I d/l-ed MathJax. Which file do i run to install?
 
I should say I don't understand your answer either. Are you saying that either x > 2 or x < 2? Perhaps you might want to add that together this is the same as x is not equal to 2. =)
@ZeeshanMahmud No file necessary. What does d/l-ed mean?
 
Downloaded
 
@ZeeshanMahmud You don't need to download anything to use MathJax in this site. You add $ $ whereever necessary and things will just work.
 
@Srivatsan I see. Test: $x \neq 2$
 
@ZeeshanMahmud Chat is a different issue. We'll come to that. You can try it in the main site.
 
6:20 AM
ok
 
As for the chat: what browser do you use?
 
Ok. Click Asaf's comment on the side bar (the one with 20 stars), and follow the instructions in robjohn's meta answer.
 
@ZeeshanMahmud Ah, I didn't think anyone else was going to bite.
 
@DylanMoreland Well, I didn't understand what the OP is asking. I don't think you did either.
 
6:24 AM
@ZeeshanMahmud Good work!
 
Thanks. I reckon if my new comment is a bit facetious.
 
Hm. I can't add numbers either. And I'm supposedly a number theorist.
 
Since you ask: it's completely off-topic and not helpful at all.
 
@ZeeshanMahmud Well, if you're going to do that, you better be correct. =)
 
@t.b How do i delete it?
 
6:28 AM
If you hover over the comment there's an 'x' appearing down on the right of the comment. Click it.
 
@tb Hi tb.
 
Hi Srivatsan.
 
@t.b. Done. I promise I will behave... :\
 
hi all
 
Thanks, Zeeshan
hi Rajesh
 
6:31 AM
FWIW though, I cannot believe this question already got an answer, yet my article-question didnt. :mad:
 
does anyone have any idea on this
 
@ZeeshanMahmud Article question?
 
@tb Yesterday, while walking back home, I realised something trivial but interesting (at least, the first time you realise it): about describing something from above and below. This is in connection with our chat with Benjamin. I was thinking about the topological closure operator, and first I thought it can only be defined from above; it didn't have a description from below.

It took a few minutes to realise that sequential characterisation is the right "below below" definition. [I know this works best in metric spaces, and needs additional work for general topologies, but ignore that.]
 
@dylan This longeur
I find this interesting.
 
I felt like I learned something for the day. =)
 
6:37 AM
@Srivatsan well, you can describe the closure of a set by limit points of nets in general topological spaces. So this works in complete generality.
 
Filters do the same stuff, right?
 
Yes.
 
Every once and a while Serre will whip out a filter and I'll have to remember what that means; I've never had to use a net.
Do you prefer one over the other?
 
@tb Yes, I know of that. I have learned it in my undergrad course (the professor emphasised the Hausdorff spaces and just mentioned the other cases). But I don't remember all details though. If I read them now, I am sure I will understand it a bit more. Oh well...
Or perhaps I am misremembering. Does Hausdorff-ness make things simpler here?
 
@DylanMoreland Not really. I find nets more useful in analytic contexts because their manipulation resembles the manipulation of sequences more closely and I find them somewhat more intuitive. However, as soon as more abstraction is involved (say with uniform structures and passing to limits e.g. completions of modules) filters are more handy.
I see that Martin just arrived, he certainly has more of an informed opinion than me on these matters.
 
6:41 AM
@Srivatsan As you plan reading about this stuff, I just want to make sure you know about P.L.Clarks notes on convergence. math.uga.edu/~pete/expositions.html (You probably do, they were mentioned in several questions here.)
I saw in transcript that you're talking nets and filters.
 
I place my request again, now that more people are here (heh). =) Can someone explain to me what filters are supposed to be all about? [Not now, some other time...]
 
Pete has notes on everything.
 
@DylanMoreland Conversely, it seems that he answers only those posts for which he has related notes... =)
Not being mean or anything...
 
@Sri : does topology (or the particular concept you are discussing) has any applications in Theoretical CS ?
 
@tb I agree with what P.L.Clark wrote in his notes and with what you're saying. Nets are better since they are similar to sequences and in most cases they are simpler. I would say the place where filters work better is when you use finer filters (which are much simpler than subnets).
Basically I would expect functional analyst to use nets most of the time and set theorist to like filters better.
 
6:45 AM
@RajeshD Well, yes and no. It has a LOT of applications in "programming languages" context. In what I do, it is but only tangentially related.
 
i guess it uses only discrete topology @Sri : this is a wild guess, please correct me
 
@tb That makes sense.
 
Well, he has notes for set theory with the tagline: "All the set theory I have ever needed to know." Heh.
 
Morrow to the what, and not of top.
 
Morning, Asaf!
 
6:48 AM
@AsafKaragila Apt entry... Hi Asaf.
 
BTW there is a notion of F-limit which generalizes both - nets and filters, I have mentioned this here. I am also in the process of writing some notes about this. I like the way that this gives unifying approach to several notions, which are defined for filters and nets, such as cluster points or limit superior.
 
@tb Interesting. I think Weil brings it up at times as well. (Notice that these are all Bourbakistes) I think I first saw it when Serre proves in Local Fields that Teichmuller lifts exist.
Maybe we need... algebraic general topology.
 
@Srivatsan So... today I shall earn the trust of the community!
 
@MartinSleziak Exactly which notes did you mean? Your link leads me to his expositions page...
 
@DylanMoreland No no no... we need more set theoretical general topology.
 
6:50 AM
@Srivatsan I believe topology and chapter convergence? I'll give an exact link.
 
@AsafKaragila I'm disappointed that you didn't yesterday :) Although you'd have deserved to be enlightened for the hard work on that one answer
 
@Asaf I was referring to this. Don't go there.
 
Oh yeah, porton's site.
@tb Oh I'll get it. I'm not done with that answer. Not by a long shot. By the next update someone will give the last for for that badge.
It's nice that I had learned so much about Cohen's second model without actually seeing a decent description of the construction.
 
@DylanMoreland I think I'll start reading about this when he gets the Abel prize
 
6:55 AM
He is living about an hour away from here, by the way.
Alex is right. (but I can see Gerry's point too.)
 
Well, I think both Gerry Myerson and Vassili are in similar situation - they can afford getting some downvotes without having really much to lose.
 
That brings me to something I was thinking in the past: Currently, Vassili gets downvotes without paying for them. If they manage to get upvotes in the future, will the points from the downvotes be deducted, or no?
 
No.
 
That's probably good.
 
7:05 AM
@MartinSleziak Thanks for this, Martin. I hope to be able to understand this answer of yours "soon". [Hopefully, that's not unrealistic.]
(tb pointed me to it yesterday.)
 
Yes, I've noticed you talk about dual of $\ell_\infty$.
 
@Srivatsan: Can you understand Gerry's answer which I linked above? :-)
 
@AsafKaragila I do, but I don't understand your point. =)
 
oh, boy, what's this?
 
That you start with answers you can understand, then you move to answers you don't understand yet. I wanted to see if Gerry's above or below your level :-P
David Roberts accepted two answers by me in a span of a few minutes or so :-P
One here and one there.
 
7:09 AM
Well, are you asserting a total order among topics (or answers)? =)
 
@Srivatsan No, but it is a lattice.
Every two answers have a join and a meet. Even if those are very very far from one another ;-)
 
I should know better than to be worked up by your comment. I must confess I was. =)
That said, I like your last comment though.
 
@Srivatsan I'm not sure I'll be in chat tomorrow and the day after tomorrow (because of exams), but this is my favorite topic (as t.b. noticed and mentioned in some comments), so I'll be glad to discuss it, if needed.
 
@MartinSleziak It's nice of you to offer help. Of course, this is not time-bound, so please concentrate on your exam. =)
And all the best for it.
 
@Srivatsan Well I only have to prepare the exam and than grade it. My students are the ones whom you should wish luck.
I am not sure whether my grammar was correct in the last sentence, but I guess broken English is ok here.
 
7:14 AM
@MartinSleziak Oh, right. What course is this?
 
@Srivatsan First course in algebra (for students of computer science) - the first semester covers linear algebra. And also some basic set theory.
The set theory course if for students, which should become teachers - how is this called in English; students of teaching? didactis?
 
@tb Thanks a lot. Now I had to delete that..
 
@MartinSleziak They call it Branch of study: Teaching primary and secondary subjects at our faculty website.
 
I've removed from a question about conic sections. I suspect it may need another tag instead. Can someone look into that?
 
Maybe ? Tag description includes systems of equations.
 
7:21 AM
analytic-geometry, algebra-precalc
 
@Martin We call them education majors.
 
Personally I call them jerks.
 
Thanks Dylan.
 
(At the two midwestern universities that I've spent time at). I don't speak for all English-speakers.
@Asaf Hah!
 
For the use on the official website, I would go with Dylan's suggestion.
 
7:25 AM
@ZeeshanMahmud me not seeing what a stack of flashcards has to do with a book you want to write (a book which in fact exists in every math library, by the way) does not mean you have to delete this answer.
 
Ok, obviously I'm just procrastinating here. See you later!
 
@tb It got a downvote plus it was community wiki. So it doesn't matter. I think it's for the best. :)
 
I have to go now, at least for a while. I'll see you folks later!
 
To help me get started on this... It's a variation of nim, correct?
 
7:43 AM
does anyone know D'Alembert's priciple ?
 
@RajeshD Why is the discrete topology useful? If someone uses only the discrete topology, then why bother using this term? =)
 
hm..
any way i am not well verse....not even a novice in topology
@Sri : just curious, how do people from TCS view subjects of the like of real analysis, differential geometry etc....have they ever been used anywhere in TCS ?
On a different note, some people ask 'where and how is it useful ?'...most of the time the problem is how do you define 'useful' ?
 
8:01 AM
@RajeshD Not sure if it answers the question, but when I used to be a CS major, we had to take discrete math. Combinatorics helps a lot for TCS...
 
@Zeeshan: Just because the word ‘discrete’ appears doesn't mean it has anything to do with ‘discrete mathematics’.
 
Are there any well known masters programs in mathematics besides the one at Cambridge?
Pure mathematics, I mean.
 
@ZhenLin That was the name of that course, 8 years ago in my school. :)
 
@Potato: There are some at Oxford too.
Part III is famous only because the Tripos as a whole is famous...
 
I've heard they aren't as selective as American graduate programs, but can afford to be because they don't provide funding.
There are a few scholarships I know of for American students to attend the Tripos though...
 
8:06 AM
@Potato: Admissions to Part III is selective. It has to be, otherwise we'd have an embarassing fail rate.
 
I sort of want to apply for Part III, but I'm concerned about cost. There aren't any good study abroad math programs I know of besides Budapest (and maybe a Russian one?) but those don't really fit in my schedule.
 
There are about a half-dozen from Harvard alone. I'm sure there's money to be had...
 
So see England, learn math? Sounds like a good deal. Of course, getting in is a nontrivial issue, but putting that aside, it's fairly costly, is it not? Especially with the current exchange rate?
 
It's cheaper than paying the full tuition rate at an American university!
 
What is it? American is like $50,000 a year at least, although I get aid.
Columbia was that much even with aid, but chose not to attend.
 
8:10 AM
It's about £15,000 in various fees. Then you have to budget for living.
 
That's actually not horrible.
There are multiple scholarships, yes?
 
Just get a Churchill/Gates/Marshall. Easy.
 
"easy"?
 
There are two Gates scholars in pure maths this year that I know of; one from Harvard, another from Nebraska-Lincoln.
 
I knew someone who was a Gates scholar, but I don't think I would be that good, even with the few years I have to prepare.
 
8:17 AM
Okay, not easy. But doable. I think the REU-type stuff helps a lot. (I'm assuming that you're in America.)
 
Yeah. I've been warned away from REUs though.
 
What were the reasons given?
They can certainly be wastes of time for everyone involved, but it doesn't have to be like that.
 
Essentially, I could do an REU, and unless I was at a really good one like Duluth, I'd just be working on toy problems.
Or I could do a reading course out of say, Lang's algebra.
And take a shot at the algebra qual next year.
 
Let's be honest: most undergraduates are not likely to achieve much on a ‘real’ problem compared to a toy problem.
 
Exactly.
So why waste the time when you could be doing something more substantial?
 
8:21 AM
Duluth is good. Ken Ono runs a good one; I think it's at Emory now. There's another one that I'm blanking on that has treated people I know well.
 
Though I am applying to the UCLA logic program this summer.
Because it sounds like a lot of fun.
 
Because nothing titillates someone on a scholarship or admissions committee more than a record of published papers. Even if it's completely orthogonal to your development as a mathematician.
Ah, I had a friend who did that.
She mostly talked about the climbing and the weather. I don't remember much about the math.
But I imagine that was alright too! I hope you get in.
 
6 hours of logic lectures a day, plus problem sessions.
 
It wasn't on last summer when I wanted to go... oh well.
 
Someone here complained about that too!
 
8:24 AM
@Potato Why the marathon?
 
I don't think my friend was even interested in logic.
UCLA is just a fun place. Unless you want to drive anywhere.
 
@DylanMoreland Right, but I can do work with professors here that is more tailored to my background and more "real".
And get papers that way.
@Srivatsan It's a three week intense program in logic.
 
@Potato intense seems to be right.
 
@Srivatsan But fun, though!
 
Good to hear. Out of curiosity, what knowledge is assumed of the participants? Is there a website or something?
 
8:30 AM
Well, no one's forcing you.
This is the only logic pun I can think of and it's awful.
 
@Srivatsan No background is assume.
 
Well, I better get to bed. It's 2 am here and I finals tomorrow (at 6 pm, but still...). Can't get a scholarship to Cambridge with a poor GPA.
Night all.
 
Ah. Good night and good luck.
 
Thanks. Have fun, @Potato.
 
8:53 AM
Is a question about Binary Search Trees on-topic?
Hi @all.
 
@Gigili it is.
 
Great, thank you.
 
9:23 AM
Are we allowed to put incomplete answers? :)
 
@ZeeshanMahmud which question?
 
Depends on the question. If it's a difficult question and it's an honest attempt, then I would be cool with it.
What exactly were you able to do in that question?
 
I only did it on paper. Let me Latex it on comp...and I will get back.
 
9:41 AM
Ok done. Where can I show it?
 
Hi!
I have test tommorow, anyone care to explain something to me about complex numbers? I feel completely lost, and after some time googling. I am still clueless =(
 
@N3buchadnezzar Sure.
 
I am supposed to solve the equation x^4 = -81
And we have not really learned anything about complex numbers, so... Sigh, I feel stupid.
 
I will first divide by $81 = 3^4$, so the equation becomes $(\frac x3)^4 = -1$. Is that ok?
 
I was thinking that the equation must have 4 soloutions, and that
$-1 = e^{\pi i}$ but thats about how far I`ve come
 
9:45 AM
@N3buchadnezzar We'll come to that in a bit.
The division is not really needed, but it makes things simpler. Think of $y = x/3$. We're solving $y^4=-1$.
 
Yeah, thats fine. Simpler is better =)
 
This kind of equation is best solved in "polar coordinates". Write $-1$ as $e^{i \pi}$ and $y = e^{i \theta}$. It is clear that $|y| = 1$, otherwise I must really say $y = r e^{i \theta}$.
 
So $$ \left( \frac{x}{3}\right)^4= e^{i \pi} $$
 
Is that clear, no? Whatever I wrote before...
 
So $e^{i \theta}$ serves at the "angle" right? and the length is one
 
9:52 AM
Yes. Now, what happens to the equation?
 
We obtain two cases, one where $y=1$ and one where $y=-1$
 
No, we do not get that.
 
"which further can ble split into two cases"
 
Not sure what you're talking about.
 
I was thinking above and below the x-axis. That $y=1$ when it is above, and $y=-1$ when it is below.
Perhaps a complex way of looking at this problem
 
9:55 AM
I am not following. Of course, $y=1$ and $y=-1$ are not solutions for $y^4=-1$, right?
 
Ofcourse not
So in reality , we are spltting $\theta$ into 4 pieces?
 
@N3buchadnezzar I suggest we do not get ahead of ourselves. =)
One second, let me think.
 
Kind of silly that our class have been introduced to complex numbers, and equations before dealing with polar coordinates (Ofcourse I have some experience with polar coordinates.)
 

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