« first day (477 days earlier)      last day (4535 days later) » 

7:10 AM
@t.b. I have succeeded applying your hints to the problem, and indeed the two axioms are already enough to characterize a group!! Thanks for your generous hints here.
 
what, is some group axiom redundant?
which one?
 
Eh, no. No axiom is redundant.
 
so what two axioms were you referring to?
 
I was talking about the group axioms in one book by Weil, where he used two axioms to define a group.
 
which ones?
 
7:19 AM
They are: (1) associativity (2) for any pair x,y of elements in G there exist z and z' such that xz=y and z'x=y.
 
that's... unusual
what could possibly motivate such a definition?
 
And I was wondering if they really can characterize the groups. Then t.b. told me that they were, and then provided some hints.
Sorry for the slow typing...
I remember I have seen such a definition in the book "A first course in arithmetic", by Jean-Pierre Serre.
 
in one way it's obvious
in the opposite way:
1) identity: take x = y
xe = x, e'x = x
hm... gotta remember how to work out uniqueness :)
 
associativity, right?
 
ex = gx = x => egx = x, so left identities are closed under multiplication, as are the right identies
 
7:29 AM
I meant for every element the same identity suffices, and then to argue the uniqueness it will be easier.
 
exists h such that he = g implies x = gx = hex = hx, so the identities form a subgroup
oh right, these are just the identities for x
left identities for x
you mean if e is identity for x, then it's identity for any y in G?
 
Yes, easily seen by the following: if yg=y, then xyg=xy.
 
ex = x => for all y exy = xy. so if x is a left identity for y then y = xy = exy = ey
right
 
True.
 
so we're now at left identities and right identities
ok
 
7:36 AM
And we can then argue that if x is a left identity and y is a right identity, then they coincide, and hence we can prove that every left identity is equal to x. C.Q.F.D.
 
if ex = x = xe' for all x then ee' = e' = e'e so e' is a left identity
ok, so now we just have identities
but for any two identities e and e' e = e'e = e' so all identities coincide
right
now inverses are standard:
or not
for any x there exist y and z such that xy = e, zx = e
then z = ze = zxy = ey = y
right
 
I have not yet thought about that yet...
delete the last yet...
 
i still have one question: why would anyone start with Weil's definition?
 
But your answer is correct!!
 
where did it arise?
 
7:43 AM
It might seem more natural for the arithmetic works??
 
more natural how?
more natural than going through the monoid route? :D
 
Then what is your incentive for the usual ones?
 
hm
will it count if i start with categories? :D
i think not
 
you can go on. I will listen.
 
well, a group is just a category with one object in which every morphism has an inverse
 
7:45 AM
ok.
 
groups naturally arise as groups of automorphisms so it's a perfectly correct insight if you allow hindsight
but i think groups always arose as groups of transformations of something
so associativity and the existence of identity makes perfect sense
 
But in the arithmetic with which so far I have ever had acquaintance, we are interested in the equation, and hence to guarantee the solvability of some equations might appear easy to understand?
 
and the existence of the inverse is also natural because it reflects the fact that often we don't want to consider transformations that lose some information
@awllower don't tell me you never had calculus or linear algebra before 0_o
 
Then remarkable it is to find out in the end that the two concepts agree with each other!
Oh I have, then ?
@AlexeiAverchenko But even in the two areae we are considering the equations, right?
 
general linear group, orthogonal group, group of diffeomorphisms of R^n, rings the bell?
so how does Weil's definition concern equations?
@awllower true
 
7:51 AM
Of course one could start with the group of transformations of something, and I was just trying to provide some motive for that definition.
 
do we identify equations with functions f: Z \to Z and call their zeros solutions?
 
And if you mind not, you can try to read the book by Serre I just mentioned; you can certainly find some pleasures therein!!
A first course in arithmetic
 
i intended to read it at some point, but so far my hands are full with at, dg and ct :)
does it require galois theory?
 
I think at this point my explanations might seem somewhat too weak... So let us agree with each other that the mathematics are consistent!!^^
Oh no, it requires not at all.
at first the first chapters not, while the last parts might be dancing with the analysis.
I mean those Dirichlet series or some kind of zeta functions, one of the most remarkable creatures in the world.
 
'a course in arithmetic' - is this the book?
 
7:56 AM
Yes it is truly.
 
it starts with a chapter on finite fields
 
Just a word, are interested in number-theory, or some works by Weil? I admire the mathématicien André Weil quite a lot.
 
are you sure 'nothing at all' is the correct description?
 
Oh yes it does.
Not at all in Galois theory...?
 
well, yeah
btw i only recently realized what p-adic norm is all about :D
it seems so simple now :D
 
8:00 AM
Glad to see that!
I am only a sophomore, therefore I am still learning some of the important theories like the measure theory for locally compact groups, and is reading the book by A.Weil to learn it. Maybe I will need your help again afterwards. Nice to meet you!!^^
 
they should've written 'it counts leading zeros in base p' in huge letters right at the start!
 
8:19 AM
it's very interesting to contrast this with real numbers
two integers are close to each other wrt euclidean norm if in any base they have many of the same digits 'counting back from infinity' (in the sense that |x - y| is small if x - y is small)
and two integers are close to each other wrt p-adic norm if they have many the same digits counting from zero 8)
 
 
1 hour later…
9:31 AM
My tutor (guy who grades homework) is not as evil as I thought. In one of the questions when I got fed up with calculating derivatives I wrote "What follows are some very long calculations which you cannot see as they are written in invisible ink. Basically, (explanation of the argument)" and I got full marks : )
 
Tutors having been doing those homework exercises, too :)
 
9:58 AM
I've received my first salary :))).
@Matt Sure, you're in the third year right? He will believe you can calculate derivatives already ;-).
 
Jonas, congratulations.
(but don't spend it all on hooch.)
 
10:28 AM
@Jonas: hi
 
11:08 AM
@Ilya Good afternoon (barely)
 
@robjohn howdy. you've seen my question?
 
@Ilya Not yet, lemme look...
 
11:30 AM
Could somebody please tell me the difference between the "Beta" and "Meta" sites is?
Also what is the "overflow"
 
@Skullpatrol could you give an example of Beta site?
 
@Skullpatrol A beta site is an experimental site where things are meant to be tested. The Meta site here is a site which discusses issues about the main sites.
 
@robjohn ... and meta sites (so there is no need for meta-meta)
 
@Skullpatrol See Meta.
 
@robjohn :-p
 
11:36 AM
@Ilya :-D
 
And overflow is just a name. Stack Overflow (the programming QA) was the original Stack Exchange -style site, and Math Overflow is a research-level mathematics site
 
@Ilya Were you previously known under another name? :-).
 
@JonasTeuwen ;)
 
@robjohn So, Math Overflow as a research-level mathematics site is not considered as being "Meta"
ie MetaMathematical
 
@Skullpatrol on MathOverflow they discuss high-level mathematical problems, on meta sites they discuss how to deal with trolls e.g.
the last one is not a high level mathematical problem, so
 
11:45 AM
@Ilya Where does "Beta" fit into this equation?
 
@Skullpatrol nowhere, simply because it's not an equation. it's an equality
 
@Ilya An equation is not an equality?
A beta site is an experimental site where things are meant to be tested.
 
@Skullpatrol you can ask it on MSE, but not on MO/this chat/any beta site
 
@robjohn I think I found my confusion... it is "meta"- site not MetaMath... right?
 
 
11:54 AM
@Skullpatrol yes, it is meta(math.se) not metamath.se
@JM: Good evening :-)
 
@robjohn Ahh ... the parentheses help a lot!! ... why aren't they used in the titles?
 
@Skullpatrol there are periods for that in the web names.
 
Good evening rob. :)
 
@robjohn Thank you for your clear explanation Sir
 
@JM It is Turkey-Day here today (Thanksgiving Day). Big feasting later today.
 
11:59 AM
@JonasTeuwen: Congratulations on your first salary!
 
@rob Yes, the comic I read daily reminded me. :D Who's stuffing the turkey there?
 
@JM My wife and I actually had our home-cooked turkey last Sunday. Today we are taking her mom out to a restaurant for dinner.
@JM So The Tam'O'Shanter is stuffing the turkey today :-)
(The Tam'O'Shanter is a Lawry's owned restaurant)
 
Ah, a subsidiary... (I was wondering about the flickering.)
 
The Tam'O'Shanter has been around for a long time (longer than Lawry's), but Lawry's bought it. Walt Disney used to eat at The Tam'O'Shanter back in the day.
 
That old, I see.
 
12:06 PM
Here is their web site.
 
12:34 PM
@tb I can't judge if he is right. Is he?
@Matt Thanks!
 
@JonasTeuwen I don't think so, he misinterpreted the notation, I believe.
 
So basically he is making a fool of himself? :-).
 
@tb Well, he claims "...whom I know well, I just wanted this to be clear to all". Maybe that's why he has the balls.
 
Well, I'm waiting for the algebraists to chime in. Have made enough of a fool of myself recently.
 
If it does precipitate Adams to join, however... :D
 
12:42 PM
@JM Wait: if you write about a dead and famous person you have the guts, while when you write about someone you know, you wouldn't? I would think the bon ton would be the other way around...
(you is the generic you of course)
 
Well, I was thinking that he feels so close to Adams that he can say that freely without fearing him...
Somewhat in the style of "oh he's nuts, but he's still my friend."
 
That's what would be fine and that's what I was trying to point out. But it's JF Adams he writes about (and I think he intends to say that he knows JD quite well)
 
Okay, clearly I misparsed the second paragraph... :D
Then yes, that is serious moxie he has.
 
"stayfocusd" is a great addon for google chrome!
The good thing is that you cannot disable it on the current day!
 
1:04 PM
@JonasTeuwen oh, so you get your first salary? that means that I should have also received mine. And congrats to you! that was a good idea to drink before you receive the salary )
 
@Ilya Yes you should have received it, but it might take a while depending on your bank (one day or so).
 
@Jonas: I have. I use abn amro
 
So do I!
 
 
1 hour later…
2:12 PM
@tb: The +1 on my last comment is from you and translates as yes, right?
 
@Matt: yes.
 
@tb: Sorry, I needed to know. I don't trust random people's opinions.
 
I was a bit lazy :)
It's the exact same argument as the one I had in mind.
 
: )
 
I bought a magic trackpad. Let's see if this helps a bit against RSI :-)).
 
2:29 PM
@Jonas: sounds good! Have fun with it, but don't spill stuff over it :) (I'm thinking of chemical apples, shoe polish and the like...)
I can't believe that this hasn't come up before, but I couldn't find an instance...
 
Hah :-).
(all apples are chemical, it were synthetic ones =))
 
Yeah, I didn't remember the word.
 
Morning.
 
@AsafKaragila Morning?!
Morning.
 
@JonasTeuwen In Hawaii or something, no?
 
2:32 PM
Shoe polish does seem to taste good.
@AsafKaragila But you're not in Hawaii, are you?
 
I am afloat a raft in the Pacific ocean. Thank god for 3G cellphones.
 
@JonasTeuwen I see that you had fun )
@AsafKaragila what is your trip about?
 
@Ilya It is about choice. Just like the whole Matrix trilogy.
 
@AsafKaragila haven't seen it. Is it a textbooks course on Linear Algebra? Like Lee's on manifolds?
@Jonas: can I ask you to check my solution of one quite basic probability problem?
 
@Ilya Of course!
(But brb)
 
What is the most general category for which differentiation and integration are adjoint functors?
Well.. maybe you can narrow it down to at least picking the objects as subsets of \mathbb{R}
Taking the morphisms as analytic functions obviously works, but anything more "general" than analytic functions seems to break down somewhere, as then differentiation is no longer a "total" functor.
 
@robinhoode Set? :-P
 
@Ilya Looks good, but I'm wondering about the existence/continuity of your cdf :-).
 
@JonasTeuwen what do you mean with the existence?
 
It seems like you're using that it is continuous in the last step.
 
2:49 PM
@AsafKaragila How do you find the derivative of a set-valued function?
 
@Jonas: what is the last step?
 
This is what the smiley was for. To denote a joke...
 
you mean this?
 
Yes.
 
hello, anyone up for a simple math noob question about series convergence?
 
2:53 PM
@Clash let's try
 
when I prove that a series converges by the Alternating series test, does it also say that it only converges, that is, it's not absolute convergent
the question is, does the Alternating series test say something about absolute convergence?
 
@Clash if you have a_n->0 only then no, take a_n = 1/n
@JonasTeuwen but we can represent it as probability of a countable union of events that $xi\leq 1/(k+1)$
 
@Ilya Oh right! No problem then!
 
@Clash I meant, take (-1)^n * 1/n
 
@Ilya but you cant apply the alternating test to a_n = 1/n, it's not alternating
 
2:55 PM
@Ilya: but why make the detour via cdf's in the first place?
 
@tb sorry, didn't get you
 
@Ilya if you do (-1)^n * 1/n, then you can apply, and you get that it's convergent but not absolute convergent. that's my question. is there any alternating serie that is absolute convergent?
 
@Clash (-1)^n * 1/n^2
 
@Clash the alternating series test says let a_n be a sequence that monotonically converges to zero. then the series \sum (-1)^n a_n *converges.
 
thanks for examples, then it only says it converges or diverges. it doesn't say if it's absolute, right?
 
2:58 PM
@Ilya Ashok's answer only uses the purely measure theoretic fact that for an increasing sequence A_n of sets the measure of the union is the limit of the measure of A_n, so I don't understand why you go via a cdf.
 
@Clash does it say if series diverges?
 
sorry, my bad ilya, it doesnt!
 
@Clash I'm not your bad Ilya )
 
yes you are!! come here sweetie! i love commas
naughty boy
k thanks guys, you're the best
 
@Clash I wish I can ask you AYAG question, but that's not polite
 
3:01 PM
@Clash: but make sure you don't forget about the monotonicity condition in the test! That's a trap that is often used in exams.
 
@Ilya I'm not a girl ;)
@tb yeah thanks for the tip, I did prove a_{n+1} < a_n
man you guys are so wise, im jealous
 
@Ilya Impolite.
 
or would it be envious... anyways ima stop flooding here, cheers guys
 
@AsafKaragila I read your discussion with Victor, I know that it is impolite and you I guess know that I'm not interested in the answer. Just that was the only reason for Clash's behavior
@tb sorry, his intentions confused me a bit. I was also wondering what are the strict bounds on the convergence
 
@Ilya Aha.
 
3:05 PM
 
@JM he left right angles for you )
 
I just remarked that "not polite" should be "impolite".
 
@Ilya Ah, I see it now. But he's way overcomplicating it.
 
@AsafKaragila I then take my justifications back :)
@JM dunno, I rather tried left right joke
 
The application looks to be just looking for grid rectangles. Oh well...
 
3:08 PM
@tb: oh, did I understand your point correct?
 
quick question, I have proved with the alternating test, that a series is convergent. Can I show that it's not absolute, by doing the comparison test on the |series| and showing that it's divergent?
 
What's up @JM?
 
@Ilya I think so.
 
@Asaf: Nothing but talking to you guys. Keeps the blues at bay...
 
@tb nice ) his answer is perfect also due to its generality, though I was interested in more information - that's why I had to use c.d.f. Do you mean you see more simple way?
 
3:15 PM
I love this weather, it's so cold, foggy and grey. I wish summer would never return.
 
I'm capped for the first time in weeks.
 
I might hit the cap too today. First time in a couple of weeks.
140 so far.
 
@Matt Can we make a deal, then? I give you my winter and you give me your summer?
 
@tb I already told you to move over here.
 
@tb: Deal.
 
3:19 PM
Trade Zurich for Israel? You must be crazy to do that :-).
4
 
Actually, does your winter involve snow?
@JonasTeuwen: I think I'd trade pretty much anything, even though I love cold.
I've been meaning to do my Master's in Tokyo but then Fukushima happened and spoiled it all : (
 
@JonasTeuwen my friend is in Singapore now ) everything is cool there, but he bothers that he will be tired of everything in half a year
 
@Matt As much as you like... I've already had enough of this. bleeeh:
 
@tb we luckily finished with fogs for some time. We even have some sun
 
@Ilya: I just posted an answer to your question. I will have to reread the accepted answer to see if I agree.
 
3:22 PM
@tb: NICE! I want one meter or two and I want it to last from November til March.
 
Nice.
 
We have warm days lately.
 
@Ilya Well, the point is it isn't real fog we're having here. Just a grey curtain about 500 m above the city, this is going to last for about four more months now, at least...
 
@tb: Not true. I live in the middle of fog. Moved here in April, it's the best place I ever lived in around ZH. It's proper fog here : )
 
I love fog.
 
3:24 PM
It is the best fog ever?
 
@robjohn thanks! I'll take a look
 
@Matt What's not true? I see no fog in the city and none around my place (over the hill), but a few hundred meters right up, but I'm bad at estimating the distance.
 
@tb at least you have some nice places to go to. I'm talking about nature rather than pubs
 
Necrophagia - The Fog
Wonderful track.
 
@AsafKaragila 10 years ago I liked CoF: her ghost in the fog
 
3:27 PM
@Ilya CoF is not my type of music.
 
@tb Well, here is still part of the city but the fog is right here, you can touch it. Feels nice to walk in it, especially in the morning. I can't argue if you were only referring to the city centre...
 
@AsafKaragila I remember, just was picking you with the only black-metal group I know :-p
almost the same time I liked Nebel by Rammstein
 
@Ilya: Indeed. Our neighbours are a bunch of cows and sheep : D
 
@Matt one friend told me the criteria how to realize where is the border between Belgium and the Netherlands, but I won't sound it here because it's not only about the cows, but also about the girls
 
@Ilya: There aren't any girls around here...
 
3:31 PM
...that sounds like a familiar gag, Ilya... ;)
 
@JM that wasn't familiar for me
 
Will anyone let me in on it?
 
@Matt around your place or this chat?
 
@Ilya Neither.
 
@Matt are you in Zurich?
 
3:32 PM
@Ilya: Maybe. Why?
 
@Ilya I was just saying that your mention of "girls" and "cows" made me remember. :)
 
@Matt I see. Well, I sort of understand the appeal. When I lived in the mountains, it was beautiful to have real thick fog (and we had snow from early November until May, too). Next time I see St. Peter, I'll see what I can arrange for you :)
 
@Matt because I thought you are a student at ETH
@AsafKaragila is it instrumental?
 
The Fog?
Parts of it.
 
@AsafKaragila it's binary, you know ) part of any song is instrumental. So yeah, I managed to reach vocal
 
3:36 PM
I'm quite excited about this Saturday: We're picking up our puppy. I've been waking up early because of it...
 
@Asaf but hell, 11 minutes. I recalled why I stopped listening to metal
 
Yeah, that's your call.
 
@tb Nice. Can you also arrange for accident free travel? I'm scared to death of driving.
 
@Matt What breed?
 
@Matt excuse me, are you excited about the puppy?
 
3:37 PM
Guess the breed:
 
101
 
@Ilya yep. I guess that makes me soft.
 
@Matt such statement or the puppy?
 
@Ilya The statement.
 
Heh. That's the puppy you're getting Matt?
 
3:39 PM
Yes. My ideal dog : ) I think she's gorgeous.
 
New question tagged lattices appeared today: math.stackexchange.com/questions/tagged/lattices
Perhaps implementing @tb's suggestion to sort them between integer-lattices and lattices-order would be useful. meta.math.stackexchange.com/q/3187/8297
 
@JM Can I do something? Or is my rep not high enough? If yes, what?
 
Maybe som of the questions tagged order-theory would be suitable for lattices-order tag, like this one: math.stackexchange.com/questions/11185/…
 
@Matt not at all, we are not in the army (aren't we?) I personally prefer cats much more, but recently my father appeared to have black Labrador. Amazing guy
 
3:42 PM
@Ilya I love all animals, they're much nicer than humans. We have 3 cats too.
 
@Matt heh, cool. prevent your puppy from them )
 
@Ilya Indeed : ) The tom thinks he's boss, last time a dog visited he thought he had to assert himself.
 
@JM: OK.
 
@MartinSleziak I agree with all you're saying. I don't have time to take care of this right now, but please go ahead.
 
3:46 PM
@Ilya It is almost already completely dark :-).
 
@tb I wasn't sure, since you wrote on meta: Before doing something, a consensus must be reached...
But I'll make the tags if you think it's ok.
It will be the first tags created by me....
 
@Jonas: indeed it is
 
@MartinSleziak I'm taking no objection (no downvote on the suggestion I made either) as a go-ahead. If people should happen to raise valid objections, we can then still merge (lattice-order) into (order-theory).
 
ok
@tb In your opinion, it should be integer-lattice or integral-lattice? See my comment there: meta.math.stackexchange.com/questions/1363/…
 
I'd go with the first myself.
 
3:51 PM
@MartinSleziak Even if integral lattice would be somewhat more tech-savvy, I believe that we already have enough confusion with the many "integral" tags, so I'd go for "integer-lattice".
 
ok, thanks
 
4:18 PM
(The names you suggested on meta.)
I guess retagging should go slowly, so that I do not flood front page - perhaps if the last question I rettaged is no longer on the first page, I might retag a new one. Does it seems a correct rate?
 
@MartinSleziak Sounds good to me. It won't look like flooding if you allow retags to fall off the front page.
 
@Martin: Links do not work in tag-wiki excerpt, so I wouldn't add them. I edited the link out from one of them. That rate sounds very reasonable. You could easily do two or three at the same time, I don't think that this would be perceived as flooding. And thanks for the effort!
 
Thanks for your help too.
 
Hello. I solved numericaly a stochastic equation 10000 + t = 1000N(t), N(t) --- Poisson process(0.01) and found it's minimal root. It's probability density has 3 local maximums. I can't interpret this :(
 
@tb Last question - should I edit this meta.math.stackexchange.com/questions/1363/… to indicate that we already introduced those tags?
 
4:26 PM
@MartinSleziak That would be great!
 
@Ilya Wrong guess.
 
@Matt then I maybe mixed up you with somebody else, sorry
 
Since we are already discussing tagging and retagging, what is a suitable tag for algebra over a field?
I've already asked this, without getting some definitive answer: chat.stackexchange.com/transcript/message/2514751#2514751
 
How many questions do we have that would fall under this potential tag?
 
@JM It's not easy to say, but I stumbled upon some such question when retagging questions having tag algebra.
Maybe a few from this google search google.com/…
This one math.stackexchange.com/questions/20829/degree-of-an-algebra is an example of such questions, which has only algebra tag.
 
4:41 PM
Okay. Now for the naming... is way too long. is alright, but a rather wide umbrella...
 
@JM Yes, e.g., ring theory is a subset of abstract algebra, but we do have a tag.
 
Ok, I've learned a new thing today. Hopefully, it will not be the only one...
 
...and , well...
 
@MartinSleziak I would say it also depends on what you want to do with these algebras. Maybe would encompass what you're looking for. For example , contain questions that would fit that tag (and yours).
 
4:52 PM
Well, I will bring this up again if I won't be able to retag some question correctly.
I did not want to create new tags, I guess two new tags are enough for one day...
 
I see :) I share that feeling that doing something about it would be useful (maybe even necessary), however I couldn't come up with a tag proposal that I really liked.
 
BTW I was browsing new tags and noticed this . (It's 4 days old.)
When new questions concerning derivatives come, should we add this tag?
(This is my last question about tagging for today, I promise.)
 
@MartinSleziak I guess it's about time. has way too many "differentiate blabla" questions...
On the other hand, do we count questions on partial derivatives? Jacobians, gradients, and Hessians?
 
@JM ok, When I see a new question in that direction, I'll add the tag.
 
4:59 PM
@tb Wide umbrella. ;)
 

« first day (477 days earlier)      last day (4535 days later) »