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1:59 AM
Hi, I've got a grammar question. 1) "f is such a function that f(0)=0" vs. 2) "f is a function such that f(0)=0". It seems that "such that" is used much more than "such a ... that". Is only 2) correct or is 1) also fine?
 
 
1 hour later…
3:13 AM
@Julius: The first is awkward English math structure. The second is correct. Of course, we could also just say "$f$ is a function with $f(0)=0$."
 
Hello Ted
Can you please explain the constant of integration that occurs when we partially integrate a function? I'm unable to understand how that constant is a function with respect to other variables except the one with which we integrating .
 
3:42 AM
I am trying to see, when $f( \overline A)= \overline {f(A)}$ is. I couldn't rule out the case that the sufficient condition is that closure of $\overline A$ is compact. Any ideas, counterexamples?
 
this Q&A is in terms of $f:X\to Y$ continuous and $A\subset X$: math.stackexchange.com/questions/236907/…
so if you want a counterexample, maybe try violating one or both premises?
 
Konformist's question is different because they're not taking further closure of $f(\overline{A})$.
Indeed, it fails for continuous $f$ even
 
oops, i see what you mean
 
Come up with an example of a continuous map which is not closed
 
The counterexamples that I find are all for the case that the subspace's closure is not compact.
 
3:53 AM
If $\overline{A} \subset X$ is compact, then $f(\overline{A}) \subset Y$ is compact (continuous image of a compact space). If $Y$ is Hausdorff, then as compact subspaces of a Hausdorff space are closed, $f(\overline{A}) = \overline{f(\overline{A})} = \overline{f(A)}$ by what SemiC linked. So it in fact holds.
But consider $Y$ to be the Sierpinsky two-point space $\{0, 1\}$ with topology $\{\{\}, \{0\}, \{0, 1\}\}$. Let $f : [0, 1] \to \{0, 1\}_s$ be the map which sends everything to $0$.
Take $X = A = [0, 1]$. Closure of $A$ in $X$ is $A$ itself which is compact, but image is $\{0\} \subset \{0, 1\}_s$, a subspace which is not closed. It's closure is all of $\{0, 1\}_s$
 
That was fast
Thank you @BalarkaSen
 
4:12 AM
TIL a song from Ne Obliviscaris, an orchestral prog metal band, was chosen for extensive study in the Sydney Conservatorium O_o
the song is "And Plague Flowers The Kaleidoscope" btw
@Alessandro @EdwardEvans @Astyx
 
4:40 AM
@Knight If you integrate with respect to $x$, holding $y$ and $z$ constant, say, then the constant of integration may be different when $y$ and $z$ vary (it's a "constant" of integration only so far as $x$ is concerned). Thus, the constant of integration is actually an arbitrary function of $y$ and $z$.
Hi @Pig
 
Pig
hi @Ted
 
trying to work some more hyperelliptic stuff
 
Pig
What's your context of doing so? Are you reading a book or?
 
tbh, i should be
i'm more just cobbling things together out of curiousity right now, which is always a bit hazardous
 
Pig
i see, that's cool
 
4:52 AM
so, to proceed: I start with the plane curve $y^2=p(x)=\prod_{k=1}^{2g+1}(x-e_k)$, with all $e_k$ distinct.
 
@BalarkaSen They chose it to be studied, but what if they analyze it for weeks and in the end the conclusions are "nah you know what, this was a mistake, the song sucks"
 
that gives rise to a hyperelliptic curve covered by two affine charts. the first is the one specified, and the second one is $w^2=v^{2g+2}p(1/v)$ subject to the glueing maps $(x,y)=(w/v^{g+1},1/v)$.
 
@Alessandro typical classical snobs
 
(I am totally stealing this from the hyperelliptic curve page on wikipedia, to be clear)
 
(I'll listen to it later, I'm not familiar with it)
 
4:58 AM
now, i think the following should be true: there are $g$ holomorphic differentials on this curve, of the form $x^k (dx/y)$ for $k=0,1,\ldots, g-1$.
each of which has a zero of multiplicity $k$ at $(x,y)=(0,0)$.
erk, i stated the gluing maps backwards. should be $x=1/v$ and $y=w/v^{g+1}$
on the intersection of these charts, the gluing maps then give me $x^k(dx/y)=(1/v)^k(-dv/v^2)/(w/v^{g+1}) = -v^{g-1-k}(dv/w)$
now, if i understand right, $dv/w$ is still regular (b/c $w^2 = q(v)\implies $2w\,dw=q'(v)\,dv\implies dv/w=2 dw/q'(v)$ is regular at $(w,v)=(0,0)$)
as such, $-v^{g-1-k}(dv/w)$ should in fact have a zero of multiplicity $g-1-k$ at $(w,v)=(0,0)$.
oh. hmm. should those multiplicities be doubled?
yeah, because one still has x~y^2 near the (x,y) origin and v~w^2 near the (v,w) origin
so I think one has in total: $\text{div}(x^k dx/y)=2k [0]+2(g-1-k)[\infty]$?
 
5:27 AM
the price of doing math in an empty room is that I forget to turn on chatjax and donn't notice the silly mistakes :/
 
Pig
loll
 
5:43 AM
@Semiclassical morning
it is not easy at all ,i tried everyhting but failed to calculate the value!
 
5:57 AM
does every component contain a path component?
 
6:08 AM
yes it does, since every path component is contained in only one component
 
@Yuvraj the z1*z2*z3 one?
 
6:23 AM
@Semiclassical Hi ! We have not talked from so many days
 
@Semiclassical yes
 
Did you remember you told me that you teach only 4-6 students at a time
?
 
i don't remember anything like that, no
 
22 hours ago, by Yuvraj
user image
this one!
 
6:30 AM
i think i have the answer to that, but i only found it by guessing
 
ok?
 
you need all three z's to be on the unit circle, so i figured i'd look for a solution where one of the z's is one
that means that the product of the other two would be 1. since they each have modulus 1, that would mean they're complex conjugate to each other
 
i thought so,ok?
 
so you'd have a triplet like 1,z,1/z. and you'd need 1+z+1/z=1.
what does that tell you about z?
 
Sammy, is fundamental principles of nuclear and particle physics still provide a heavy scope of research ?
 
6:34 AM
Sammy?
 
Semi
 
Same pronlunciation :-)
 
i'd say so, but it's not anything i can say anything interesting about
 
z +1/z +1 look like hyperbola
 
6:36 AM
you're not plotting it
i'm asking you to solve 1+z+1/z=1
 
ok
 
$$z+ z^2 + 1 = z\\ z^2 =-1$$
$z=\iota$
 
z=i
 
right. z=-i would work too, but then 1/z=i and it makes no difference
 
and yes
 
6:39 AM
so 1,i,-i fulfill the conditions about the sum/product/modulus of the z's
however, which one is which as far as z1,z2,z3 go?
 
Semi, do you appreciate the current researches that are going on in QM? I mean they seem to be more like an engineer than Physicists, they don’t focus on fundamental principles rather they are working on some specific behaviour of some specific substances. Like the potentials of Silicon crystals, analysing the behaviour of helium plasma and what not.
It’s not Physics, it’s engineering
 
um, no
understanding how specific systems work is perfectly good physics
engineering is figuring out how to use those specific systems to accomplish another task
 
Okay, but these researches differ from early 20th century (and earlier) researchers. I feel there is a major difference
 
sure, because there was more open to discover
 
@Semiclassical i
 
6:43 AM
as far as fundamental interactions go, anyways
 
have yu notice the condition for imaginary part
 
yep.
that's what i was asking you to notice
so which is which?
i.e. which z goes with 1,i,-i
 
yes
 
Which field is still open for fundamental development?
 
yes
 
6:46 AM
shrug I dunno. "fundamental developments" aren't that interesting to me. i'm more interested in figuring out what neat things nature can do with the theories we understand, than endlessly speculating about what is 'fundamental' in nature
particularly given how unproductive that seems to be at the presentn moment in history
 
z1 with -i
 
Wow! It feels good talking to you
 
and z2 =0
 
um. 0 doesn't have modulus 1.
so z2=0 makes no sense
 
What it means when someone writes something between four dots. Like :: shrug:: or ::purr purr:: (with italics)
?
 
6:48 AM
it's an emote
i.e., you imagine the other person doing that action
(quite how a person would 'purr' i don't know)
 
Hahahahaha
Dmckee does.
But I respect him
 
i meant z2=1+oi
 
Semi, with which subject did you do your major in undergrad?
 
i did both physics and math
 
Wow.
 
6:51 AM
a pretty straightforward double major, all things considered
 
@Semiclassical one is z1=-i
and z2 would be real
 
right, and z3?
 
and z3 would be =i
 
right. so (z1,z2,z3)=(-i,1,i) will satisfy the conditions
in which case, what's the answer?
 
Semi, what’s the fundamental difference between the Engineering course and B.S. courses. Because anyone with engineering Compter Sc. have to have study higher mathematics
 
6:58 AM
i don't know, really: i never went down the engineering route
though it's also tricky b/c there's so many different kinds of engineering
 
Okay. How did learn programming? On your own? Wow!
 
mechanical engineering, electrical engineering, aerospace engineering, civil engineering, chemical engineering
learned by doing, mostly
though i always find it a bit awkward to say that I'm a "programmer"
i know how to use certain programs to do mathematical computations
 
:-)
 
but if you asked me how to program in C++, i wouldn't have a clue
 
Which language do you know?
 
7:00 AM
there's a certain degree of 'programming' required to use mathematica, but it's not reall the same thing
probably matlab is the one I've the most experience with?
 
@Semiclassical got it answer is 2
 
Do you design simulations in Python?
 
no, and I wish I knew how
python is one of those things I keep thinking I should pick up some experience with
 
@Semiclassical can you confirm
 
You’re true Physicist
:-)
 
7:02 AM
that's what i get too, yeah
 
After all, we can hire programmers for making simulations for us. We are paper workers not computer users :-)
 
of course, this approach relied on the solution having z=1
which i only got by guessing, not by any sort of deduction
if the correct z1,z2,z3 weren't so simple, i'd not have found them
so I feel like I got lucky to find that solution
 
 
2 hours later…
9:13 AM
@BalarkaSen That track is awesome
 
9:31 AM
@Astyx Definitely one of my favourites. Probably Xenoflux is my favourite from that album.
 
@LeakyNun I... don't know why you have tagged me in this :P.
 
hint: a pawn
 
Another hint?
Probably a reference to my name?
 
yeah
 
9:40 AM
Ah it is, lol.
Nice
Maybe my pronunciation of 'a pawn' and 'apón' differ from yours.
 
how would a Greek say "a pawn"?
 
You mean someone with a greek accent?
 
It's pronounced Απών
 
right
 
I'd have to ask one ( a greek) :P
Are you still working on Lean @LeakyNun?
 
9:46 AM
right
 
Is that built on C?
 
C++
 
Someone at a lunch about a year ago (who wasn't an expert in computer science by any means) said (and I'm paraphrasing non-faithfully I'm sure) C isn't absolutely reliable, so any theorem-prover that is built on C can't be trusted with absolute certainty. Does that seem like a valid concern to you?
 
those are likely extreme cases
so no
 
10:27 AM
@Balarka tbf it's Ne Obliviscaris
crazy music
 
Truth
@Astyx Ya
@LeakyNun Chess community getting angry on Naka
 
@BalarkaSen wait what
I thought they're supporting Naka and getting angry on Ben
 
chess24 got angry on Naka for stealing the stream right
I was watching penguinz0's rant on the situation
 
There was a youtube video of a guy commenting on that saying it's complete bullshit and that the chess community need to stop gatekeeping chess and stop being so elitist
 
10:43 AM
Yeah penguinz0
The greatest drama commentator of all time :P
 
Oh yeah that's the guy
He's got style :p
 
@Astyx play me
@BalarkaSen basically everyone is jealous of Hikaru for having so many views
 
11:01 AM
yeah lol
 
The twitch chat has gotten less enjoyable since the qvc-hikaru streams (although those are hilarious)
 
@Present 7777777777777777777
 
MonkaS
 
And some of the chess streamers are playing much less chess
 
WeirdChamp
 
11:11 AM
I thought this was hilarious though
@BalarkaSen Everyone love Naka, except ben finegold and chess24
If you say you like Naka in Finegolds stream, he'll probably ban you, he banned me for that
 
Lol
 
Although his wife unbanned me, so you can probably do that :P
 
It'll be fun if xQc viewers jump on Ben's chat
He'll turn off the chat itself
 
He'd get instantly banned for sure
I think xqc won't do that though. He seemed genuinely sad when he watched ben finegold insulting him
There were a few other incidents that aren't as well known
Like Eric from chessbrah getting ultra drunk and going on a 30 min rant
And part of that was about xqc
 
Oh what
What did he say
 
11:21 AM
I think it's been scrubbed from the internet
Let me see if I can find it, posting the content would get me chat banned lol
 
Eric apologized it seems
 
Yeah he's going sober until August or something after this
Aman turned off the stream a little after that min^
Because Eric was going wayyy too far lmfao
 
Yikes
 
Now he's reformed though
He lost 15 times in a row to danya, and the chat were saying xqc was better than him and shit to stir him up, that's what generated the rant
 
Classic Eric, it's so easy to piss him off
 
11:26 AM
Have you played against him before?
 
Nah I just watch I don't play chess
casual viewer
 
Ah okay. If you wanted to play him and get stomped, you can claim in the chat that you'll stomp him, and if he gets mad, he'll play you
 
Lmao brilliant
 
It's so strange that the chess drama has moved into mainstream meme-culture
 
Yeah this is great
 
11:28 AM
Penguinz0 talking about it feels so strange
 
Good time for us gossip consumers
 
:D
Are you in third year now?
 
Nah, at the end of second year
which doesn't seem to end
 
Are you going to go overseas for phd?
 
Doubtful
Are you an ungrad, or?
 
11:30 AM
It's me Alex C
three weeks from finishing masters
 
Wait, which Alex
Oh
Clark
 
Yep
 
Dang man we missed you here
@Present Congrats in advance!
 
Thanks :)
I'll talk here more after finishing. I'll be a research assistant for like 6 months before starting PhD
 
11:32 AM
Coronavirus messed up standard phd funding apparently
 
white to move
 
@LeakyNun wut
Ah
Yep I see it
That's actually a really cool tactics problem
 
@LeakyNun is thiis a chess problem, or something else?
ah
 
It's from a Magnus game (he is black). White has a winning tactic
(white gets huge material advantage unless there's also a mate in x that I'm not seeing)
 
There is a mate
Not sure how many useless moves black can play to delay it, but Qc6 restricts the d7 square, and the rook can't move anywhere to stop Ra8 mate, the b7,c7 pawns can't move anywhere useful, and if bxc6 then bxc6 again holds b7 and d7 meaning Ra8 is mate still
material gain you're talking about is Qb1 I guess
 
11:40 AM
Well what's the first move of your forced mate? Because c5 Kd7 and I see no mate
 
Qc6
 
Ah I see it now
 
Nuts
 
The c5 line I had in mind ends with white up a rook
 
i thought it was a queen sac but did not see it
 
11:42 AM
It's probably like a 2300 puzzle on lichess
 
i was trying qb7
 
Yeah I think he can just take that with the king, and he escapes (if you play qb7 sac)
 
If his queen wasn't threatening mate (after black bishop takes) then you could lift both your rooks for mate
 
11:44 AM
@BalarkaSen same
 
@LeakyNun Holy crap, the speed at which he could recognise the mate is insane
 
My c5 idea was to get a pawn on c6, which can be stopped only by losing material from white, but Qc6 gets the pawn on c6 unavoidably
 
wait, what if black goes Qb1
 
@LeakyNun on what line?
 
so 18. Qc6 Qb1+
 
11:47 AM
Qc6 Qb1 Rxb1 bxc6 bxc6 and you have the pawn on c6 which was needed to mate
 
@LeakyNun You still just get Rxb1, and then pawn takes queen, pawn retakes pawn, and the same mate
 
yeah but then Kb8
 
@LeakyNun Rba1
 
Kxa8
oh I forgot the rook is still there lmao
I thought there was only one rook
 
LOL
 
11:48 AM
hmm, stockfish proposes just pushing the rook to a8 immediately
and then in a few moves gives mate
 
This is why playing blindfold is hard, among other reasons
 
Your rooks are in the wrong spot
 
oops
ok, yeah, now it spots it
 
There are cases where stockfish fails to see the best move for like 20 seconds even with 32 cores
 
11:51 AM
yeah, i can imagine
 
One of those sorts of games occurred in a recent tournament
The first magnus invitational
 
There are some positions where a human can tell at a glance "black has a lot of checks but eventually I'll get my king to this square, he'll run out of checks and I can finish my winning attack" while the engine gives a 0 evaluation because it can't compute far enough to see the end of the checks
 
Yeah, need more cores, and greater depth for some of those
 
lol, if you follow stockfish to the end of the sequence (when Black runs out of obstacles to throw up) it just does a useless pawn move for Black
"meh, doesn't matter at this point"
 
That's best play, and he's not allowed to resign (except after 400 moves or whatever on lichess)
 
11:54 AM
right
 
It's the best move, in the sense that it works in the greatest number of white-not-actually-taking-the-checkmate-lines
 
In the TCEC the game ends when both engines agree that a side has a winning advantage iirc (I don't remember what the exact treshold is, maybe like +/-10)
 
the computer games are very droll, in the endgame they just blockade and shift around pieces
super subtle positional advantages
 
Like a priori, white could play a stupid move instead of playing checkmate
 
11:56 AM
yeah, fair
 
Stockfish can also be set up to play with contempt for its opponent
 
@BalarkaSen Not leela
Leela plays seemingly insanely dumb moves in end games sometimes, and then wins somehow
 
oh yeah i dunno these machine learners
 
If there is a move that can be refuted, but only by a crazy 3200 elo tactic stockfish won't play it. If it's playing with contempt it will because it'll assume the opponent won't spot it
 
Possibly it literally has machine learned an exploit against stockfish
@AlessandroCodenotti Yeah, that's fair
 
11:57 AM
@Present Leela also drew some winning endgames in the TCEC some seasons ago though
 
"Black can only win if White has a stroke in between the next move, so that's how I have to play"
 
Yeah people laugh at its end game strat
 
lmao
 
@Semiclassical It is better than resigning
It's also why I don't resign :')
 
11:58 AM
>oh I blundered 11 material, hmmm
 
Leela sometimes looks like a positional prodigy who never opened an endgame book
 
>Win by dirty flag
That's fair Alessandro
 
it's an attitude i've seen discussed re: card games, where (if you're losing and have no other option) you just have to play as though you'll draw exactly the right card at the right moment
 
I'd resign in longer time controls
 
Yeah, I resign if it's 10+0, and this happens with more than like 3 min left on the clock
 
12:00 PM
Just yesterday I played a 15+10 on lichess where my opponent blundered a queen on move 13 or so, but he had to make me waste 20 minutes to play it all out
 
Yeah I wouldn't do that
@Semiclassical I think it's more satisfying for the opponent for you not to quit in most card games
 
tbf, if i was playing, i'd probably do that and not realize it
oh, sure
 
@AlessandroCodenotti Did they lose though
 
asking the right questions
 
I mean, sometimes you'll stop playing properly because you already expect to win
Or sometimes your opponent will turn on an engine
 
12:02 PM
yeah
lol
 
Mainly on chess.com :')
 
the culture re: resigning does depend a lot on the game, though
 
@Present Yes
 
How many arrangements of A, B, C, D, E, F, G, H are there such that A

and B are between C and D ?
 
To be fair I immediately gave back the queen because as soon as I get a huge advantage I stop paying attention and blunder lol
 
12:03 PM
Yeah that's what I had in mind
 
But even after that I was up a minor piece and had 5 good pawns against 3 messed up ones
 
You know you'll win, so you just start playing badly
 
So I forced myself to play carefully and won
 
@AlessandroCodenotti any idea about what is best chess engine right now ?
 
lichess.org/4MVfBUPhHygV that's the game
Hard to tell
 
12:04 PM
Were they meming you, wtf is their opening
They spent 6 seconds to find a6
 
@Present No idea
I had never seen that before, but it's obviously nonsense so I was like I guess I'll just ignore it and develop some of my stuff
 
a6, Ra7 wut
 
Lmao
 
I'd expect that from a smurf
 
@Present Next level counter for my bishop on g2 lol
 
12:06 PM
hahaha
 
But the real blunder they made was not playing Nxd5 on move 13
 
My god, they spend 120 seconds on move 22, they were torturing you
 
I know...
 
I better get back to thesis writing, cya guys
or should I just watch chess24 hmmmmm
MagzyBogues vs BagzyMogues, wtf
 
We should make a math chat study group for chess
4
 
12:13 PM
0
Q: Arrangements and permutation

maths studentHow many arrangements of $A, B, C, D, E, F, G, H$ are there such that $A$ and B are between C and D ? Attempt : I am trying to solve this problem using simple counting process like first place can be occupy by 6 persons second occupied by 6 and so forth I tried to manipulate remaining one. But ...

 
12:34 PM
@Balarka general topology is too weird
 
12:52 PM
i was solving question on arithmetic sequences a doubt I have related to properties of a sequence if i say 1/b+c,1/c+a,1/a+b are in ap and if multiply every term by a+b+c then the terms will become a+b+c/b+c ,a+b+c/c+a,a+b+c/a+b
then does not change the sequence i feel it does not change the of sequence
and the same way if I add -1 to each of the new terms the sequence again won't change, so I get an idea what we can and what we can't do in the numbers ,but i do not have this data in a generalized way
can anybody help?
like what kind of operation we apply on ap?
 
1:52 PM
@AlessandroCodenotti maybe you're too cynical; it takes skills to convert a winning position into a win
and as you said, you blundered the queen back right away
demonstrating this very point
I wouldn't say your opponent is torturing you
 
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