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00:09
@Bram28
In your last paragraph of your answer http://math.stackexchange.com/q/2171958, you would benefit from changing the line: "All we assume is that P(n), so it will take some work to go from there to P(n+1)."

To

All we assume is that $P(n)$ implies $P(n+1)$, so it will take some work to go from there to $\forall n P(n)$.

It appears that the misinterpretation some people have made is reading that last line as containing $\forall n P(n)$ and $\forall n P(n+1)$ as opposed to $\forall n [P(n) \implies P(n+1)]$ .
 
1 hour later…
01:33
@AkivaWeinberger hola
3B1B made a new thing
(an anniversary episode)
Ya he lo visto
@AkivaWeinberger Oh, yeah, I saw that. It was really well done.
aunque los ideas en la video son viejos
Solo english en el chat muchachos (?
01:38
@Maks well if you like
De donde eras ?
Hong Kong
...
@Maks Hablas espanol?
@AkivaWeinberger The group theory one?
01:41
hi @Akiva
Hey everyone!
@ZachHauk Yep, no se notaba?
Pienso que él es argentino
@CompulsiveMathurbator Yeah
@AkivaWeinberger quien? no pienso que Maks habla espanol como su idioma materno
@Maks Ah, si, me dijiste que tu eres de Argentina
01:45
@DHMO Maks
Tengo que ir ahora, lo siento
Pero ahora voy a celebrar el cumpleanos de mi madre
@DHMO Oe k kieres desir kon ezo ?
Adios
Adios
@Maks kiero desir k ablaste "de donde eras" en lugar d "de donde eres"
01:47
Porque una vez me habias dicho de donde eras
Por eso, de donde eras ? yo sabia el dato y ahora lo perdi
No se porque lo decimos en pasado
Es como un amigo te conto algo y vos te olvidaste, y le decis como "era" esa cosa?
Ustedes no dicen asi?
@Maks yo te habia dicho "de donde eras"?
He vuelto. Es tan frío fuera. Voy a esperar dentro
Ese no habla español ponele jajaj
@Maks I don't understand
@DHMO jajajaj vos me habias dicho el pais del que eras
@AkivaWeinberger :D that you're a lovely person but spanish isnt your mother language
01:53
Was my syntax strange in what I just wrote?
@Maks de donde venes?
@DHMO De la cocina
q?
vengo de la cocina jajaja
tenes idea como funciona la notacion de bases esta ? $[S]_{B,C}$
pienso que sos de argentina
01:55
$B$ es una base que me dan y $C$ es la canonica
@DHMO Yep
Seria la matriz de cambio de base de B a C ?
@Maks conozco una amiga que iba a argentina por un ano
ah mira vos, se venia hasta aca por un ano? yo le pondria una "ñ" por las dudas
:p
le gusta a toda la gente anos :p
jajajajaj
02:15
@BalarkaSen @AlessandroCodenotti We see that 1,2,3,... do not converge under the usual topology in $\Bbb N$. However, if we include $\omega$, they would converge to $\omega$. I can't say that $\Bbb N$ isn't closed, because every set is closed in their topology. How shall I say it instead?
Hi guys. could anyone please give me hints about this question math.stackexchange.com/questions/2172314/…
Thanks
02:40
hi @Mike
@ZachHauk hola
@MikeMiller do you have any idea about my question above?
@DHMO como estas?
estoy bien
I'm always so confused trying to derive formulas for when I have to make a function where the next term is some number added to the previous term... it's definitely exponential, but added sounds like multiplication not repeated multiplication..
02:44
tengo que escribir un ensayo que analiza dos poemas sobre tecnologia >.>
hola
@CausingUnderflowsEverywhere how is it exponential?
@CausingUnderflowsEverywhere it is multipllication...
as a subset of $\omega +1$ in the order topology $\Bbb N$ is not closed
x ( whatever ) didnt seem right when I graphed
02:45
@MikeMiller but can we not reference other topologies?
@CausingUnderflowsEverywhere try mx+c
@DHMO estare un nino de 14 anos en 23 dias :D
@ZachHauk bueno
mx + c is basically without the exponentation, it needs to be like
term 1 $5 + 50$ , then t2 - $t1 + 10 + 50$, then t3 - $t2 + 15 + 50$
@CausingUnderflowsEverywhere I won't describe that as "some number added to the previous term"
and it isn't exponential either
so $t_n = \displaystyle \sum_{i=1}^{n} (5i+50) = 50n + 5\sum_{i=1}^n i = 50n + 2.5n(n+1) = 2.5n^2 + 52.5n$
03:02
it's quadratic :D
/ es quadratico?
@ZachHauk es cuadrático
ah yes
few words in spanish start with q
except que, quedar, querer, etc
I dont see a 4 anywhere, if anything it's doubtic, or ditric , or perhaps bitric
03:04
@CausingUnderflowsEverywhere quadratic means having a degree of 2
yeah, the term "Quadratic" comes from "quad" meaning square, rather than 4
degree 4 is called quartic
well quintic means power of 5 therefore
no
not all latin roots are the same
quad also means "square", not just 4
it's cool my markup will still be readable
03:06
@CausingUnderflowsEverywhere you can't impose your own words on the community...
similar to how it's
sorry Im not on the community just anyone who reads my markup
"cubic" instead of "Tritic"
markup??
:35834820 you can try calling it "bitric" and "tritic" and see how many people understand
as in, HTML
03:06
I think "markup" means "notation"
yeah im just messing with him :P
where are you from? @CausingUnderflowsEverywhere
nope markup like YAML ain't markup language
I'm from CA nice to meet you ^^
@ZachHauk I think he's just trolling here now
yeah I was joking from the start ..
thanks for introducing me to summation DHMO
03:07
you are welcome
btw
stay away from DHMO
my grandparents died after being exposed to DHMO :(
It's the leading cause of drowning
In fact, most people have already been exposed to high concentrations of DHMO
and DHMO gas may cause DHMO rain
03:11
Im sorry but your attempt at luring me to your website to obtain my IP address from a pool of recent visits will not work.
...?
It's a joke, DHMO is H2O
Additionally, your IP address would not give us any valuable information
oh it would tell you what city I live in
Unless we had a botnet, which most random guys on the internet don't
Yeah, and how does that help us in any way?
AND if Im at some library or educational institution, you could actually know what building Im inside
Uhh no
03:13
you could find me and beat me up for trolling? :/
Unless I knew that library or institution's IP address beforehand, no
No I couldn't find you, I could find your vague location, which may be off by up to 10 miles
@CausingUnderflowsEverywhere even so I'd have a hard time finding you
If I wanted to find you
First I'd get your vague location
Travel there, and listen for loud obnoxious babbling
It's not even DHMO's website
:^)
(I'm kidding, too)
03:14
actually I guess you don't know the power, you just need to look up who owns the net range of the IP and some individual libraries own their own net range, and have the library name in the organization name so... unfortunately you can find the exact location of some people just by looking up their IP
Are you in a library or educational institution?
That I cannot share.
:P
By the way, a lot of ISPs have so-called "Dynamic IP"
which would render that information kind of useless...
yup, and there's pesky PEOPLE WHO SHARE THEIR LOCATION giving away where the IP has been assigned to, making IP location more accurate
so sad..
03:16
btw I just entered the website, now what dihydrogen monoxide in newark
That's not even his fucking website...
My IP also is in Newark, by the way, even though Newark is pretty far away from here
why are you swearing
I'm using spiced vocabulary
Profanity is the spice of language, then.
why do you add chili peppers to your vocabulary? someone might be allergic
I was joking @DMHO, Im sorry
aw man
03:26
Hey everybody relax ! I am BAYMAX :)
Hello BAYMAX, thank you for relaxing us
now let's talk about math
Ohhh!
$t_n = \displaystyle \sum_{i=1}^{120} (5i+50)$
that's $5\left(\sum_{i=1}^{120}i\right)+ 50*120$ when you distribute
$n$ here ?
03:30
now, do you know the formula for summation of the naturals?
it's $n(n+1)/2$, so you get
$(120*121)/2$
soooo

$t_n = \displaystyle \sum_{i=1}^{120} (5(n(n+1)/2)+50) $
you evaluated the sum
then put it inside the sum
$t_n = (5(n(n+1)/2)+50) $
what to do with 120
oh n
$t_n = (5(120(120+1)/2)+50) $
03:33
no
$t_n = (5(60^2+60.5)+50) $
is that better? o.o
@ZachHauk I dont quite understand the distribution
ok so let's write this out then
we have
$(5 + 50) + (10 + 50) + \dots$
so let's split this up
$(50 + 50 + \dots) + (5 + 10 + \dots)$
now, how many $50$'s are there?
the 50 is really a constant, but every term we add up the amount of that term then, dump it into our sack of totals
we accumulate
so 120 50s
120(50)
04:01
@DanielFischer Actually, I can seemingly only prove that $$\lim_{y \to \infty} \int_{-\infty}^{\infty} \frac{\pi \sin (a(x-iy))\cot(\pi(x-iy))}{x-iy} \, dx - \lim_{y \to \infty} \int_{-\infty}^{\infty} \frac{\pi \sin (a(x+iy))\cot(\pi(x+iy))}{x+iy} \, dx = i 2 \pi^{2}$$ for $0 < a < 2 \pi$
04:42
That integral scares me
 
1 hour later…
05:44
hello, @DHMO
@Vrouvrou bonjour
bonjour, pouuvez vous s'il vous plait m'aider, je cherche une 2eme méthode :math.stackexchange.com/questions/2172181/…
@Vrouvrou je ne comprends pas la question
étudier la continuité de la fonction en utilisant deux méthodes
je ne comprends pas la fonction
05:51
les ouverts sont $\mathbb{R}$ et tout ensemble $A$ tel que $[x_0]\in \mathbb{R}\setminus A$ où $[x_0]$ est la partie entière de $x_0>10$
la fonction , elle donne 0 lorsque $x\notin \mathbb{N}$
et 1 lorsque $x\in \mathbb{N}$
c'est la fonction caractéristique sur $\mathbb{N}$
quel est $x_0$? @Vrouvrou
où $[x_0]$ est la partie entière de $x_0>10$
quel est $x_0$?
any number
just >10
pourquoi avons-nous besoin de $x_0$ si $[x_0]$ est entier quand meme?
06:02
je ne sais pas c'est l'exercice qui dit ca
as-tu le livre?
What's up ladies & gents.
I think I have an efficient smallest grammar algorithm and P = NP
That's all, just sharing
Prepare for global economic collapse in network security
Not likely though, but I do have an approach not looked at yet
@DHMO non c'est un examen de plus on a besoins de la partie entière car on étudie ;la continuité de la fonction caractéristique sur $N$
@Vrouvrou alors je peux dire, par exemple, que $x_0=100$?
06:10
alors juste appliquez la definition de continuite
oui jutement je ne sais pas comment
$\Bbb N \setminus [x_0]$ est un ensemble ouvert
et $f(\Bbb N \setminus [x_0]) = 1$
this is the same idea give by Henno Brandsma
je veux une autre méthode
c'est ce qui est demandé , démontrer en utilisant deux méthodes
06:14
considere le fait que une fonction est continue si l'invers de un ensemble ouvert est aussi ouvert
oui c'est la meme réponse que j'ai eu math.stackexchange.com/questions/2172181/…
@Vrouvrou j'ai aucune idee
vous ne savez pas comment on montrer que $f(\overline{A})\not\subset \overline{f(A)}$ ?
quel est $A$?
n'importe le quel
on a cette propriété
$f:E\rightarrow F$ est continue sii $\forall A\subset E, f(\overline{A})\subset \overline{f(A)}$
06:20
d'accord, laisse-me penser
soit $n=[x_0]$
@DHMO merci
j'ai reçue une autre réponse
soit $A = \{n\}$
$\overline A = \{n\}$
$f(\overline A) = \{1\}$
$f(A) = \{1\}$
$\overline {f(A)} = \{1,n\}$
@Vrouvrou ok I start again
soit $A=\{0.5\}$
$\overline A = \{0.5,n\}$
$f(\overline A) = \{0,1\}$
$f(A) = \{0\}$
$\overline{f(A)} = \{0,n\}$
alors $f(\overline A) \not\subset \overline{f(A)}$
@Vrouvrou ^
salut
06:28
siema
nie mówiÄ™ po polsku
@DHMO je n'ai pas compris comment ou calculé $\overline{A}$
because I didn't learn it? @CausingUnderflowsEverywhere
he doesnt understand your comment on calculating overline A
@CausingUnderflowsEverywhere no, "comment" means "how"
06:30
you're right and I am wrong
@Vrouvrou $\overline A$ est le reunion de $A$ et ses valeurs d'adherence
aussi, $\overline A$ est le plus petit ensemble ferme qui contient $A$
he doesnt understand how in calculating overline A ?
et les ensembles fermes sont les ensembles qui contiennent $[x_0]$
@DHMO you say $A=\{0.5\}$ , then $\overline{A}=\{0.5,n\}$
?
@Vrouvrou oui
$n$ est le seule valeur d'adherance de $A$
06:33
pourquoi ?
parce que $\{x\}$ ou $x \ne n$ est ouvert
mais le seul ensemble ouvert qui contient $n$ est $\Bbb R$
le seul ouvert qui contient $[x_0]$ est $R$
oui
par exemple $\{1\}$ et ouvert dans notre topologie
exactement
06:36
oui donc je ne comprends toujours pas votre raisonnement
comprends-tu pourquoi $n$ est un valeur d'adherence de $A$?
quel est un valeur d'adherence?
c'est la limite des sous suites
quelle est la limite?
06:39
la limite ou converge les suites
quelle est une limite?
c'est qui tout ses voisinages contiennent un nombre infinie d'élément de la suite
mais quel est le valeur d'adherence des ensembles?
$t_n = \displaystyle \sum_{i=1}^{120} (50 + 5i) $
$t_n = \displaystyle \sum_{i=1}^{120} 50 + \sum_{i=1}^{120} 5i) $
$t_n = \displaystyle 120 * 50 + 5 \sum_{i=1}^{120} i) $
$t_n = \displaystyle 120 * 50 + 5 * ( [120(120 + 1)]/2 ) $

Is this correct for the summation of the following sequence?

$50 + 5, 50 + 10, 50 + 15 $ which contains 120 terms?
@CausingUnderflowsEverywhere yes
06:42
why thank you @DHMO ...
let me see if I can go back and understand the way Zach did it
oh lol I did the same thing kind of he just skipped one step
@DHMO une valeurs d'adhérence est la limite de la suite ou celle des sous suite convergente
@Vrouvrou et la valeur d'adherence des ensembles finis?
je ne connait pas]
une valeur d'adherence de l'ensemble $A$ en la topologie de $X$ est un point $x \in X$ tel que tous les voisinnages de $x$ contiennent un point de $A$
comme la limite de la suite $S$ est un point tel que toutes ses voisinages contiennent un nombre infinie d'element de la suite
 
1 hour later…
08:07
Hi @Alessandro
Good morning
08:37
Is the interior of a cube homeomorphic to the interior of a unit ball?
Yes.
It doesn't matter if you look at the whole thing, not just the interior.
08:50
Are all open, convex and bounded subsets of $\Bbb R^n$ homeomorphic?
Actually without bounded
Yeah.
In fact star-convex suffices I believe.
they're contractible so homotopy equivalent but that's much weaker than homeomorphic, I don't know how to show that
Hirsch has an exercise somewhere which furthermore asks to prove they are all diffeomorphic to R^n. I have no idea how to show this; I can give you a proof for n = 2.
@Alessandro Note that an open contractible submanifold of R^n need not be homeomorphic to R^n. Example.
that's extremely weird
and its product with $\Bbb R$ is homeomorphic to $\Bbb R^4$!
Right.
09:02
R. H. Bing was called exactly like that, the R and H are not initials of a first or middle name
That's Bing for you!
What did I expect from a guy with such a weird house!
Not just that. He's the collection of all the crazy weird things in the topological category.
yeah I've seen the dogbone space (it was linked in the Whitehead's manifold page)
He showed that if you glue two Alexander horned balls (do you know what those are?) along the boundary it becomes homeomorphic to the 3-sphere. Which implies existence of wild involutions on S^3.
09:08
That's the embedding of a sphere in $\Bbb R^3$ with a weird complement right? (and I forgot what exactly weird is supposed to be here)
Alexander horned sphere is an embedding of S^2 in R^3 with one of the connected components of the complement not homeomorphic to a ball (in fact not even simply connected).
The horned ball is the non-simply connected component.
but doesn't a cube have vertices?
so its interior has some punctures?
Huh? No
The vertices lie on the boundary
yes
@BalarkaSen topology is weird
09:15
Agreed.
To prove that $\pi_1(X\times Y,(x_0,y_0))=\pi_1(X,x_0)\times\pi_1(Y,y_0)$ the point is that if $\alpha$ is a loop in $X$ based at $x_0$ and $\beta$ is a loop in $Y$ based at $y_0$ then $\gamma(t)=(\alpha(t),\beta(t))$ is a loop in $X\times Y$ based at $(x_0,y_0)$.
Now if $F$ is an homotopy between $\alpha$ and $\alpha'$ while $G$ is an homotopy between $\beta$ and $\beta'$ then $H:X\times Y\times I\to X\times Y$ with $H(x,y,t)=(F(x,t),G(y,t))$ is an homotopy between $\gamma$ and the loop $(\alpha'(t),\beta'(t))$
That only gives a map $\pi_1(X, x_0) \times \pi_1(Y, y_0) \to \pi_1(X \times Y, (x_0, y_0))$ though.
What about a map in the other direction?
hmm, right, so if I have a loop in $X\times Y$ I can project to $X$ and $Y$ to get loops there
That's right. So the same recipe for homotopy gives you a map $\pi_1(X, x_0) \times \pi_1(Y, y_0) \to \pi_1(X \times Y, (x_0, y_0))$.
All you have to verify is that they are inverses (as group homomorphisms), and you'd be done showing an isomorphism.
but that's ez
Nice, I'll think about the details
09:28
There are a lot of nice problems in Chap 1.1 in Hatcher by the way.
This chat's successfully transforming you into a topologist, much to Ted's dismay I guess!
lol
I still haven't done the exercises in Chapter 0
(In fact I still have to read the part about the homotopy extension property, we didn't talk about this in class)
Don't read the homotopy extension property. It'd be very unmotivated until you get to homology.
It's a nicety property for pairs of spaces (X, A). If you work with a CW complex X and it's subcomplex A it'll always hold.
Is it a generalization of the fact than you can quotient by contractible subcomplexes without changing the homotopy type?
I see, I'll do some exercises and jump to chapter 1 then
09:42
Yup.
10:31
Good morning, guys!
11:12
Excuse me?
I am an undergrad that's trying to begin reading fundamental papers in theoretical computer science. That being said...
Can somebody give me their thoughts on set theory vs. type theory? I'm familiar with some of the basic axioms from axiomatic set theory and why it exists due to Russel's Paradox, but I'm confused how type theory split off on a different tangent.
I know type theory is important along with set theory, and I know that category theory is similar in vein to set theory, but I am unsure how to understand the positioning of the different theories together
And then... how does this relate to the current stuff with homotopy type theory?
Thanks
hey good morning :)
Wait a minute
am I in the wrong room
it's a math chat
@VermillionAzure
Is anyone familiar here with matrix solving on wolfram alpha?
I am doing some network analysis in an electrical circuit
and got that solving matrix :
@jublikon State-space?
{{1,-1,-1,-1,0,0,0},{0,0,1,0,-1,0,-1},{0,0,0,1,0,-1,1},{1,-1,0,0,0,-1,0},{0,0,R_‌​3,-R_4,0,0,R_7},{0,-R_2,0,R_4,0,R_6,0},{R_1,0,R_3,0,R_5,0,0}}.{I_1,I_2,I_3,I_4,I_‌​5,I_6,I_7}={0,0,0,-Q_2,0,Q1}
but wolfram alpha does not recognize that...
why ?
I followed the way the script told me.
11:28
Meh.
I dunno.
Why not use Matlab or Octave?
Or even Python + Numpy?
Hi Balarka
I thought Wolfram is a tool for everything...
haha
Hi @Danu
@VermillionAzure look at that
this was a presentation in the university
they have told us to to such a matrix
But how to solve such things ?
11:34
hm
I will think about it
but thank you
@jublikon Matlab/Python perhaps
I mean, if you're gonna deal with matrices...
hm no. it must be something that has to do with the circuit
so now I am in the wrong room ^^
11:57
Hi chat

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