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12:00 AM
and he's looking in the other direction
 
@anon Is that your son?
 
twin?
 
seems altogether rather unlikely
 
@infinitesimal "Avoid Excess. Live life in harmony and balance. Avoid excesses. Even good things, pursued or attained without moderation, can become a source of misery and suffering. " - The Ten Golden Rules on Living the Good Life
 
Thanks @Chris'ssis for sharing :-)
 
12:43 AM
@Chris'ssis two of which are "avoid excess"
 
Hi pal.
 
is there a mahematical way to deduce why the chicken crossed the road?
 
1:06 AM
@robjohn I usually don't like these lists of rules.
Hey @DavidWheeler around?
 
Has anyone studied sensitivity of PageRank algorithm?
 
1:54 AM
I guess my avatar stopped changing now
 
2:06 AM
No, I'm not a pipe.
 
@DavidWheeler wat
 
It's a twice-removed reference to Magritte
 
Have to Google Magritte
 
He would paint a picture of a pipe, labeled "Ceci n'est pas une pipe" (this is not a pipe)
Which, of course is true, it's a PICTURE of a pipe.
Which is something mathematicians make the mistake with, too-a representation of a structure, is not the structure itself.
 
2:14 AM
Anyway, i was answering Jasper, but he left. -Sobs-
 
Ah well.
 
2:30 AM
@DavidWheeler @ʙᴀᴅᴀᴛᴍᴀᴛʜ I am here.
 
Hi @ABeautifulMind
 
The past two months have been the worst period in my life. But it has made me see what has been going wrong and what is most important to me.
 
That's good progress
 
I am now targeting to get well by the end of next year, which is something I have said many years, but I believe this time it will happen.
 
But to do that, I will need to do some incredibly crazy things that will make a lot of people know I am crazy. I pray for the courage to do them.
 
What kind of crazy things?
 
@JasperLoy As long as they are safe crazy things and don't harm anything
 
I mentioned part of my OCD is to check taps and switches right? A lot of them are outside home.
I will need to get the help of people outside to check certain things, in some cases.
I know this sounds very vague.
 
I humbly suggest to make some kinds of progress you will need some ERP (exposure and response prevention) therapy. In other words, working on your need to do certain things to reduce your anxiety.
 
2:44 AM
Ah, I have a lot to say about that. Well, there are some things I need to check and some things I don't, so there is ERP already.
So I will just cut down to check the things I need to check, and check them once and for all, and move on with life, and prevent future occurrences. Again, very vague.
 
To make a crude analogy-the sound of a tiger roaring nearby understandable creates a natural response to flee. With OCD, the innate alarm signal gets triggered by similar things that aren't actually an imminent danger.
 
Yes, I know all about OCD and ERP. But it's not as simple as they say in the textbooks.
 
No, it's not. If done under the wrong circumstances, it can do way more harm than good.
 
Let me talk about medication. The serotonin theory is not as simple as they say in the textbooks either. It's not really proven, it's just a theory.
 
So, for example, you have to trust your therapist-and that takes time to establish.
 
2:47 AM
Some people will say I am disputing science about SSRIs, that's because they have not read enough of the literature. I am not saying it doesn't work, just saying there is no solid proof they do work.
 
Neurotransmitters are complicated, and we don't understand well how they mediate feelings.
 
But I will start meds soon, and when I am more stable, I will think about therapy as well.
I have done a bit of both before, of course.
It's important not just to make progress, but also try not to retrogress, which can happen easily.
 
GABA, for example helps regulate serotonin in the brain, but only the GABA our body manufactures in the brain "works" because of the blood-brain barrier.
And a lot of things we do affect GABA production in our bodies-diet, sleep cycles, etc.
So it's not just "here, take this pill, and all better"
 
Statistics are also manipulated to get drugs approved.
Sometimes, three month stats is not good, so they submit one month stats to get drug approved.
 
On the plus side, Jasmine green tea is a good natural source of GABA, and non-toxic to boot.
 
2:56 AM
Anyway, this OCD is just one part of my problems.
 
SSRI stands for selective serotonin reuptake inhibitor-it merely prevents you from depleting your existing serotonin levels-if these are already low, they won't do much good.
ecstacy (or MMDA) is a serotonin agonist, it makes you feel "happy", but at the cost of below-normal serotonin levels for days, sometimes weeks, afterwards.
 
You know much about drugs.
 
Well, for my own condition-I wanted to know "why"
 
Are you still on meds?
 
The human brain is a fascinating thing, too. I don't take meds anymore. I had mixed experiences with them.
 
3:03 AM
I am eating a fish burger.
 
I think in your case, Jasper, they will be of some help, but you're a special case, and I really think you need someone who will "stay with you long enough" to see the big picture.
 
I think my mental problems are complicated. Even I don't really understand them.
 
It's not just the present, or the immediate future that needs "balance", you have your past to come to terms with, too.
I had days when I could not get out of bed. The world was too cold (not talking about temperature).
Any little thing, checking the mail, making breakfast, gave me feelings that felt like nails on a chalkboard sound.
 
What will you say is the reason you are depressed?
 
A lot of things I thought contributed. How many of these things actually did-I dunno.
 
3:09 AM
Sounds like me.
 
I felt alienated from people in general. In large crowds, I would find myself getting angry at the ease at which people moved through life, and the utter banality of what they were doing.
 
For me, I dislike a lot of the politics and culture of my place.
 
I hope that you can either: a) move to somewhere else, or b) (more likely) find other people who understand and share your views.
 
I will try to move somewhere else once I get well. But I need to get well first, lol.
 
Do you have somewhere quiet you can meditate?
 
3:15 AM
Yes, at home.
 
Does it help?
 
It might help to calm me down and make me see things more clearly.
Have you ever been to my place?
 
I think it safe to say I've never seen your room
 
I mean my country.
 
No, never been. I know a little about it.
 
3:23 AM
There are like shopping malls everywhere. That's about the only good thing for me. I love to walk in shopping malls, and not buy anything.
 
Mostly Chinese, with a minority of Malay, and a slighly smaller Indian minority. Former British colony (hence the official language). Politics is dominated by the PAP, laws are fairly strict.
Not so bad for an ang mo, lah?
 
What time is it there? It's 11.30 am here.
 
in Texas, 9:30 PM
 
Texas is a very conservative state right?
 
Indeed, very right-wing, pro-Christian, anti-gay, anti-welfare, anti-union.
 
3:35 AM
I am going to do some thinking and then go to bed, good night.
 
OK, I hope you go to sleep wanting to wake up tomorrow :)
 
4:04 AM
@DavidWheeler I could not sleep, I will go in an hour.
 
hmm. i feel like this bit of matrix algebra should have a nicer answer than i know how to find
i've got a matrix product $VV^{T}$ where $V$ is lower triangular
and what i'd like to do is take the principal square root of that product
 
@Semiclassical How are you feeling today?
 
eh, alright. coming off of a cold
still coughing more than i'd like, but feeling a lot better than i was yesterday
 
Hello @robjohn I feel tired because I have been running in your mind all day, lol.
 
4:25 AM
@ʙᴀᴅᴀᴛᴍᴀᴛʜ Still here?
 
No one is ever here. Here is not a place. It's distributed being.
 
Ah I was about to log off and you appeared.
 
Chat moves too slow for my taste. I get bored and watch television.
 
I am not in the mood to watch TV these days.
You live with your gf right? Then things should not be so boring.
 
Having a gf does not translate into mad romance every night.
 
4:36 AM
Euler and Pontryagin got blind right? Interesting how they can still do math.
 
Darn it. I can't find the question I was looking for.
 
You can do a lot of stuff "in your head"
 
Sometimes, I compare myself to these people, wondering if I would prefer to have a physical problem or a mental problem.
 
Hard to say until you get there.
 
Yes. Like Stephen Hawking who has ALS. That sucks too.
 
4:42 AM
A lot of things suck. You do the best you can.
 
@TheEmperorofIceCream Sure. Look at classifying space of chickens.
There are a lot of chicken bundles you could study, for example.
 
@DavidWheeler That is right. The problem is that sometimes your best seems inadequate. Life is hard.
@BalarkaSen I didn't know you talk crap.
 
Well, now you do.
I talk crap a lot when I feel like it.
 
There are so many things that can go wrong with a person. Life is a struggle.
Life is already so hard for humans, think how bad it is for animals.
 
@Kaj!
 
4:46 AM
Hi Kaj.
 
Hey hey
 
Unfortunately, I have to go.
 
Hie thee hence
Since chickens are homeomorphic to crows, I suggest we study crow bundles, instead.
 
@kaj Will you change your pic soon?
 
@DavidWheeler, $\text{Chicken} \cong S^1 \times S^1$ ?
 
4:52 AM
Now everyone is crapping, except me, cos I am crap.
 
@ABeautifulMind, haven't thought about it lol
 
I am really going to sleep now, good night.
 
5:25 AM
@KajHansen indeed, because gastrolation
 
 
2 hours later…
7:29 AM
hello
 
hey there
 
7:47 AM
The problem is the following. I have a two sheeted covering map $p:\widetilde X\to X$; and I want to show it admits a unique $\Bbb Z/2\Bbb Z$-covering structure.
So, I have a pretty good idea (I think) of what I should be doing.
 
You need only contruct a covering map of order two
and you can do that by lifting the map $p$ along $p$ «with the wrong basepoint»
 
Drats. I wanted to edit.
Oh.
I get it.
 
a $z/2z$-covering structure is a covering with group of deck transformations of order two?
 
@MarianoSuárez-Alvarez I mean I want to make $C_2$ act on $\widetilde X$ such that each multiplication is an homeo and such that for each $\tilde x\in\widetilde X$ there is a nbhd $V$ of $\tilde x$ such that $g\neq h$ implies $gV\cap hV$ is empty.
 
ok
that is, then, the same as construcing a covering transformation for $p$ of order two
 
7:51 AM
OK.
 
pick a point x in $\tilde X$, and lt $y$ be the other point in $p^{-1}(p(x))$
you construct a map $s:\tilde X\to\tilde X$ such that $ps=p$ and $s(x)=y$
 
Yes.
My problem is I have to make $s$ continuous.
 
well, you have to use the lifting criterion for covering maps
 
OK. I realize I was rewriting the idea of the proof of that when I started to try to glue neighborhoods properly.
Silly.
 
you have a map $f:(Z,z_0)\to(X,x_0)$ and a covering $p:(\tilde X,\tilde x_0)\to(X,x_0)$, and you want a map $g:(Z,z_0)\to(\tilde X,\tilde z_0)$ such that $pg=f$.
you know how to construct lifting of paths along a covering
use the same idea
 
7:55 AM
Alright.
@MarianoSuárez-Alvarez Mariano, do you have any idea on the time schedule of your course?
 
I intersected what I got from you people and the intersection is empty
 
Classic. =)
 
on monday I'll try to find a schedule which leaves the least possible people out
 
Well, Monday I can do after 17:00.
 
I don't mean to have classes on monday: on monday I'll try to figure it out :D
 
7:58 AM
Ah, OK.
 
if everything goes well, on monday I will be finally done with assigning jobs to everybdy
so I am back into real life
 
Right. You're almost done!
I beg you don't do it on Monday or Thursday before 5 pm. I have courses that day from 8 to 17. =/
How many people signed up?
 
i need someone to discuss this question with me math.stackexchange.com/questions/1178050/…
 
@PedroTamaroff quite a few
I hope to be able to find something good enough for most
 
@MarianoSuárez-Alvarez I promise I won't read any material before taking the course.
 
8:00 AM
haha
 
@MarianoSuárez-Alvarez How does "deck transformation" translate to spanish?
 
transformación de revestimiento
 
8:56 AM
Guys, please avoid posting only your questions like that, and avoid that style. You can use the [text](link)code to get smaller links. I would rather you post here if you had a specific doubt about your question (perhaps a user posted something and didn't explain a detail, and such user is away).
@Johnson @PaulPlummer
 
@PedroTamaroff Sorry, will keep that in mind.
 
sorry,I know
 
user134177
hi
 
user134177
I need a counteraxample
 
user134177
Let A, B two C*algebras and f:A->B is a isometric homomorphism of algebras (which means: f is linear and multiplicative), then it should not follow that f is involutive
 
user134177
9:11 AM
could you give me an example ?
 
9:33 AM
@ABeautifulMind Try to do so without cleats next time >8(
 
9:47 AM
@robjohn helo
hello
have you seen my question ?
 
 
2 hours later…
12:03 PM
How can I go about showing that if $F$ is a field, then $F[x_1, \ldots , x_n]$ is not a PID for $n>1$?
 
 
1 hour later…
1:08 PM
@robjohn It's so quiet in here.
 
@ABeautifulMind Shh... you'll wake them.
 
Excuse me, Could someone verify this upload.wikimedia.org/wikipedia/en/math/7/2/a/… ? Also, good morning/evening to all here!
 
@ʙᴀᴅᴀᴛᴍᴀᴛʜ Hello Bart.
 
@ABeautifulMind Now you've done it!
 
Sorry to interrupt guys.
 
My condition is very unstable these days. I can feel OK now but a few hours later I feel terrible. Need to try to calm down and stabilise my thoughts. Maybe the meds will help.
 
Hi
Anyone here can help me to prove the set $S=\left\{(x,t)\in\mathbb{R}^n\times\mathbb{R}\;|\;\;t<||x||\right\}$ is open? math.stackexchange.com/questions/1179354/…
 
Yea @JasperLoy You're always up when I'm up, and we're in different timezones
 
@ʙᴀᴅᴀᴛᴍᴀᴛʜ I don't sleep regular hours. I think about things, and then I feel tired, and then I rest for a while, and then I think about things again.
 
1:34 PM
Hey @DanielFischer!!!
I am given the recurrence relation $T(n)=T(n-1)+n$.
Couldn't we solve it as follows?
$$T(n)=T(n-1)+n\\T(n-1)=T(n-2)+(n-1)\\T(n-2)=T(n-3)+(n-2)\\ \dots \\ \dots \\ \dots \\ T(2)=T(1)+2$$

At the step $i$ we will have the formula $T(n-(i-1))=T(n-i)+(n-(i-1))$.

Does the recursion end when $n-i=1$ or when $n-i=0$ ?
 
@evinda That depends on whether $T(1)$ or $T(0)$ is given as the base case.
 
@DanielFischer It is given that Τ(n) is constant for $n \leq 2$.
So does the recursion end when $n-i=2$?
So is the last relation this one: T(3)=T(2)+3 ?
 
@evinda Under the given condition, yes. That means $T(2) = T(1)$ rather than $T(2) = T(1)+2$.
 
@ʙᴀᴅᴀᴛᴍᴀᴛʜ I am going to take a nap, good night.
 
@JasperLoy Have a good nap
 
1:47 PM
@DanielFischer So is it right like that?
$$T(n)=T(n-1)+n\\T(n-1)=T(n-2)+(n-1)\\T(n-2)=T(n-3)+(n-2)\\ \dots \\ \dots \\ \dots \\ + \ \ T(3)=T(2)+2\\--------- \\ T(n)=T(2)+n+(n-1)+(n-2)+ \dots +2 \\ =c+ \sum_{i=0}^{n-2} (n-i)=c+n \sum_{i=0}^{n-2} 1- \sum_{i=0}^{n-2}i \\=c+n(n-2+1)- \frac{(n-2)(n-1)}{2}=c+n^2-n-\frac{n^2-3n+2}{2} \\ =c+ \frac{n^2+n-2}{2} \in \Theta(n^2)$$
 
@evinda Not quite, your recurrence for $T(3)$ is wrong, and hence the formula is a little off. Not much of a difference, however.
 
@DanielFischer I corrected it..
$$T(n)=T(n-1)+n\\T(n-1)=T(n-2)+(n-1)\\T(n-2)=T(n-3)+(n-2)\\ \dots \\ \dots \\ \dots \\ + \ \ T(3)=T(2)+3\\--------- \\ T(n)=T(2)+n+(n-1)+(n-2)+ \dots +3 \\ =c+ \sum_{i=0}^{n-3} (n-i)=c+n \sum_{i=0}^{n-3}1- \sum_{i=0}^{n-3} i= c+n(n-3+1)-\frac{(n-3)(n-2)}{2} \\=c+n^2-2n- \frac{n^2-5n+6}{2}=c+\frac{n^2+n-6}{2} \in O(n^2)$$

Do I have to set T(n)=c for $n \leq c$ or don't I have to since at the exercise it is given that T(n) is a constant for $n \leq 2$?
 
That formula holds for $n \geqslant 2$, but not for $n \in \{0,1\}$. So to be fully correct, you need to distinguish the cases if you give an explicit formula. Doesn't matter for the complexity of course.
 
@DanielFischer So at the beginning when I write the recurrence relation, could I write the following?

$T(n)=T(n-1)+n, \forall n \geq 3$ and $T(n)=c, \forall n \leq 2$
 
2:13 PM
@DanielFischer Great :)
The exercise asks the following: Give asymptotic upper and lower bounds for $T(n)$. Suppose that $Τ(n)$ is constant for $n \leq 2$. Make your bounds as tight as possible, and justify your answers.
Doing it as above, are our bounds as tight as possible or do we have to prove that $T(n) \in \Theta(n^2)$.
 
@evinda "As tight as possible" means you need the tightest possible upper and lower bounds. Most of the time that gives you a $\Theta$ [here we can do even better, $T(n) \sim \frac{n^2}{2}$], but sometimes you may get something like $T(n) \in \Omega(n\log n)$ and $T(n) \in o(n^2)$ as tightest bounds.
 
@DanielFischer A ok.. So do I have to say $T(n) \sim \frac{n^2}{2}$ or can I just say $T(n) \in \Theta(n^2)$ ?
 
How should I know what your teachers expect? I guess they expect $\Theta(n^2)$, but maybe they're interested in the constant factors too.
 
@DanielFischer I also think that they expect $\Theta(n^2)$. Thanks for your answer!!! :-)
 
Greetings
 
2:31 PM
@DanielFischer @TheEmperorofIceCream Could you take a look at my question?
http://math.stackexchange.com/questions/1178804/execution-time-of-function
 
srry I have a test in thirty minutes
 
@TheEmperorofIceCream A ok... in which subject?
 
It's a competition
in undergraduate math
 
Good luck @TheEmperorofIceCream
 
2:36 PM
I don't know why but I lol'd @ this comment math.stackexchange.com/questions/1179505/…
 
Could someone verify this http://upload.wikimedia.org/wikipedia/en/math/7/2/a/72a1058ad2087aec467af24bddcf9479.png ? Also, good morning/evening to all here!
@Chris'ssis Could you verify?/
 
@Kugelblitz It seems fine at the first 1 second looking (it must be viewed in the spirit of the Riemann sums).
 
user134177
hi
 
user134177
2:52 PM
i will repeat my question a last time.
Let A, B two C*algebras. do you know an example of a map f:A->B wich is a isometric homomorphism of algebras (which means: f is linear and multiplicative), but does not preserve involution?
 
@Chris'ssis Hi, I cannot remember the song you share last time. (My laptop is dead..)
 
@Chris'ssis Perfect :-)
 
emm, hi
is anyone around to guide me through a really simple line formula?
ok I'll just drop it
 
3:06 PM
@NicholasK What's your question?
 
I want to extend a line
The data I have is this
current x1,y1 x2,y2 and the distance I want to extend it
How can I calculate the new x2,y2
?
 
Extending the length of the segment with respect to $(x_1,\,y_1)$ or with respect to $(x_2,\,y_2)$?
 
well with respect to x1,y1
The problem is that I'm trying to write this down in Javascript
 
Ooooh, I don't know any Javascript :(
 
That's not the issue
The issue is what is the formula behind it?
e.g I know how to calculate the slope of my current line(which would be needed to calculate the new x2,y2 for extending it).
    var slope = (y2-y1)/(x2-x1);
    var d = Math.sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
 
3:13 PM
@Kugelblitz not necessarily like a Riemann sum though. Use this $$\sum_{i=1}^{n}\sum_{\large m=2^{i-1}}^{\large 2^i-1}$$
 
where d is the final slope
 
The slope would be the same, since you're extending a line segment, correct?
 
Hmm... Is the final result in terms of $(x_1,\,y_1)$?
 
x2 and y2 values
I already know x1,y1 and it's my current starting point which I don't wanna chage
 
3:16 PM
OOooh
So you're trying to move $(x_2,\,y_2)$ in such a manner to preserve slope and to create a segment of length $d$?
 
Sorry, I'm a bit tired this morning xD
 
Hello @NicholasKyriakides!!! Is your name greek?
 
3:19 PM
I am aldo from Greece... Where are you from? @NicholasKyriakides
 
Nicosia, Cyprus
 
@NicholasKyriakides Ti spoudazeis?
 
@DanielFischer Have you ever seen this problem ? Consider $2n$ points in $\mathbb R^2$. Prove the existence of a line that splits the points into exactly two groups of $n$ points (no point should lie on the line)
 
Dulevo, computer science
esi?
@teadawg1337 any ideas?
 
@Nicholas I'm mulling it over. Is $d$ the distance between the initial two points?
 
3:21 PM
@NicholasKyriakides Eisai programmatisths? Spoudazw efarmosmena ma8hmatika..
 
@teadawg1337 Nop thats the length I want my line to have after I calculate the new x2,y2
 
@LeGrandDODOM Never seen it, but: There are only finitely many slopes of lines passing through more than one of the points. Pick a slope such that any line with that slope passes through at most one point. Move it.
 
@evinda Ne filaraki. Phd kanis i ptixio?
 
@NicholasKyriakides Ptuxio..
 
Kaloo, ego programmatistis ime alla me blockarune ligo afta ta mathimatika re gmt. Exo ena project gia ena pelati kai exi na kanei poli me geometria
 
3:25 PM
@NicholasKyriakides Sthn Agglia ergazesai?
 
@evinda Kipro ime twra!
 
Aha! @NicholasKyriakides
 
@evinda Na su pw, kseris ligo na me voithisis me auto to prama pu eksigisa apo panw
?
 
@NicholasKyriakides Ki egw asxoloumai me thn plhroforikh.. exw parei auth thn eidikeush..
@NicholasKyriakides Tha dw kai tha sou pw..
 
@evinda na se kala, kai kala ekanes - mathimatika kai pliroforiki kanun kala mazi
 
3:31 PM
@Chris'ssis Well, I came across that as part of my solution to one of my questions here; math.stackexchange.com/questions/1160003/…
Also, @Chris'ssis I will start the bounty on that question of yours I recently asked you about in the cimments.
*comments
 
@NicholasKyriakides To d einai to mhkos tou euthugrammou tmhmatos h h klish?
 
klisi!
@evinda Klisi
 
@Kugelblitz OK
 
3:56 PM
@Nicholas I've got nothing....
WAIT!!!!!
Light bulb moment
 
Ok im here!
hahaha
 
user129943
How do I do a dot that means "put the thing in here" that is smaller than a \bullet? in LaTeX
 
user129943
For example a norm, you would write "Function $\|\bullet\|:V\rightarrow\mathbb{R}$"
 

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