Mathematics - 2013-03-31 (page 2 of 3)

Dominic Michaelis

4:05 PM

what solution would be expected here

Git Gud

4:15 PM

For lulz.

Mohamed Alaa El Behairy

is there are a place where people organize reading groups?

Dominic Michaelis

lol

Jayesh Badwaik

"Also, you incredible imbecile, there is a tag for REGRESSION, which is what I am doing here."

He sure is regressing. :P

Git Gud

So funny.

I'm laughing my ass off.

Jayesh Badwaik

might be worth a flag. :P

Git Gud

4:19 PM

I want him to be here. In my opinion MSE lacks humor.

Dominic Michaelis

@GitGud i once talked to an engineer which said he is studying algebra, and I was surprised, till he told me that algebra is solving linear equations :D

Git Gud

@Dominic It's really sad, people from other degrees refer to linear algebra and algebra indistinctively. Probably not their fault, they don't know better.

Charlie

Hmm

Dominic Michaelis

@JayeshBadwaik i flagged him for saying that

Charlie

Why?

Jayesh Badwaik

4:23 PM

@DominicMichaelis Ahh, thanks. but I guess I provoked him by making the IQ comment. So, its okay.

Git Gud

Funny shit.

Jayesh Badwaik

@Charlie Here

Charlie

@JayeshBadwaik children...

Where's Skull??

Dominic Michaelis

4:40 PM

Oh i just wanted to comment that my solution is indeed easy but i guess that would be very impolite to the op

Charlie

Ok

Dominic Michaelis

wen someone downvotes you does the cap go down ?

Arkamis

Happy easter!

Dominic Michaelis

thanks

Git Gud

@DominicMichaelis I might be misunderstanding you, the way I read your question the answer is obviously yes. I mean obvious in the sense that I've seen it happen so many times and so have you, I'm sure.

Dominic Michaelis

4:52 PM

i mean suppose you got 200 reputation today, now you get a downvote and have 198, and when you get an upvote do you have again 200 reputation or stay at 198 ?

Git Gud

Flacchus is so funny:

Flagged this post for moderator attention. – Did 11 mins ago

@Did Thank you, you don't need to. It's getting enough attention as it is. – FlacchusMaximus 1 min ago

Charlie

@arkamis Happy easter, Ed!

Jayesh Badwaik

Hahahahaha.

Git Gud

@DominicMichaelis Why would it stay at 198? I don't see any reason why it wouldn't go up to 208 if you got an upvote on answer. But who knows...

Arkamis

@DominicMichaelis You stay at 198.

Jayesh Badwaik

4:53 PM

If you get an upvote at 198, you get 2 points for the upvote and you go to 200. I think it happened with OldJohn recently. But I might be wrong.

Arkamis

You can only get 200 total per day from upvotes.

Not net 200.

Jayesh Badwaik

I see.

Git Gud

Ohh, I had no idea there was a 200 upvote cap.

Arkamis

Yeah, 200/day from votes

You can exceed that from accepts, accepting answers, and bounties.

Git Gud

I got it, thanks.

Arkamis

4:55 PM

I think we tested this recently.

Charlie

Hmm

user19161

5:24 PM

I am black and I am back.

Charlie

@JasperLoy :)

user19161

@Charlie I am still laughing over what we said yesterday in email.

Charlie

@JasperLoy hahahahahahaha

user19161

@Charlie That will be our secret!

Charlie

@JasperLoy shhhh

Dominic Michaelis

5:27 PM

@jasper how are you banananda =

user19161

@DominicMichaelis Is that from Ananda, the Buddha's disciple?

Dominic Michaelis

now its short for banana panda

user19161

The other famous disciple is Kasyapa.

Charlie

@DominicMichaelis I thought so cute when you said "bananinos"

user19161

@dominic What is your favourite algebra book?

Dominic Michaelis

5:29 PM

@jasper never read one :(

user19161

@DominicMichaelis How about analysis book?

Dominic Michaelis

i was told in only listened to calculus till now, i only read german indroduction boots

i read about the first 100 pages of metric spaces of non positive curvature in english

user19161

Herbert Amann has written 3 great volumes.

user19161

Germans are the best in everything!

user19161

The only thing they did bad was Adolf Hitler.

Dominic Michaelis

5:31 PM

he is from austria ;)

user19161

Sorry! As long as they speak German!

user19161

Ha, I must learn German too!

Dominic Michaelis

but what he did he did in Germany so you are not totally wrong

Charlie

Hitler was not german

Dominic Michaelis

@Charlie that's what i meant to say

user19161

5:33 PM

How I wish all German math books are translated into English!

Charlie

@DominicMichaelis ah, I wrote and didn't see youuuu did to :P

Carpediem

@JasperLoy Hello. Can you help me with this? math.stackexchange.com/questions/347386/max-and-min-of-fx-y

I posted a comment under the answer

user19161

@Carpediem Hi! Not that I don't wanna help you, but I am only a banana.

user19161

I have forgotten many things I studied long long ago.

user19161

So better not to ping me.

user19161

5:34 PM

But I am sure this site or chat has many competent people!

Carpediem

@JasperLoy Including partial derivatives? :)

user19161

@Carpediem Yes. I only remember 1+1=3 now.

Dominic Michaelis

@carpediem why you don't use lagrangian multipliers?

Carpediem

@DominicMichaelis I don't know what that is

yet...

Dominic Michaelis

oh thats bad luck for you

user19161

5:36 PM

See, you must ask the great Dominic instead.

Carpediem

@DominicMichaelis It's the comparison that is giving me trouble

@DominicMichaelis I posted my issue as a comment under the answer

user19161

@Carpediem My specialty on this site is algebra-precalculus, lol.

Dominic Michaelis

is it x^1/x ?

you know that x * ln(x^(1/x))=ln(x) is or ?

Charlie

@DominicMichaelis don't say that!

user19161

Anyway, I still have many old answers left to edit.

Carpediem

5:41 PM

@DominicMichaelis Yes

user19161

I can only do 5 edits on old posts a day.

Dominic Michaelis

@charlie it's in the real case we take the principal branch and can sleep well ;)

user19161

After I have finished editing them to my satisfaction, I will delete my account, lol.

Carpediem

And we obtain $f(x,x^{\frac{1}{x}})=-x^{\frac{1}{x}+1}$
Then $f(x,\frac{1}{2})=(-\frac{ln(2)}{2}-\frac{1}{2})x-\frac{lnx}{2}$
and $f(x,1)=-lnx-x$

Charlie

@DominicMichaelis what?

Carpediem

5:43 PM

@DominicMichaelis

Dominic Michaelis

number 2 and 3 are obviously monotone decreasing and numer 1 too

@charlie ln(a^b)=b * ln(a) is not true in the complex plane when having branch discontinuities

Peter Tamaroff

Math pickup line: "Wanna come to my home, so I can show you the exponential growth of my natural log?"

Charlie

It's nit what I meant but nvm

user19161

@PeterTamaroff OMG!

Dominic Michaelis

@Charlie ah lol i see ;)

@jasper how does a mathematican call his dog and why?

Carpediem

5:45 PM

@DominicMichaelis And we obtain $f(x,x^{\frac{1}{x}})=-x^{\frac{1}{x}+1}$
Then $f(x,\frac{1}{2})=(-\frac{ln(2)}{2}-\frac{1}{2})x-\frac{lnx}{2}$
and $f(x,1)=-lnx-x$

Charlie

@PeterTamaroff your d* in a box HAHAHAHAHA

user19161

@DominicMichaelis I remember hearing this one but cannot remember the answer.

Dominic Michaelis

@carpediem you got a monotone decreasing function and you search for its maximum, where do you search ?

@Jasper Cauchy, cause he leaves a residue at every pole

user19161

@DominicMichaelis lol

Carpediem

@DominicMichaelis ...

Dominic Michaelis

5:48 PM

@carpe as a monotone decreasing function is monotone decreasing, you are searching at the smalles x possible ...

Charlie

@dominic you're making him have more questions than answers...

user19161

Actually, whether you use monotone increasing or increasing makes no difference to me. They mean the same.

user19161

Some use increasing and strictly increasing allowing and not allowing equality respectively.

Dominic Michaelis

@charlie it's not my fault when he didn't pay attention in calculus is it ?

user19161

Some use non-decreasing and increasing instead respectively.

Charlie

5:49 PM

@JasperLoy I will email you soon...

Carpediem

@DominicMichaelis Forget it

user19161

@Charlie So exciting!

user19161

Similarly, some use \subset and \subsetneq for subset and proper subset.

Dave

hey

user19161

While others use \subseteq and \subset respectively.

Peter Tamaroff

5:51 PM

You all need this guys

Dave

so I have this homework about phone numbers ( combinatorics ), and found the solution, but I dont understand it anyone can help me ?

0

Q: How many 10 digit phone numbers have at least one of each odd digit?

Can some one please help me with this? How many 10 digit phone numbers have at least one of each odd digit? $1,3,5,7,9 = 5!*10^5$ I hope this is right. Or did I double count?

combinatorics

Dominic Michaelis

@peterTamaroff you should use an array for a matrix

user19161

Guys did you see what I just saw?

user19161

When I clicked on the link above, I saw the UI saying "Chat with an expert".

user19161

Is that a new SE feature to invite users to come to this chat?

user19161

5:54 PM

Or is my eyes playing tricks on me?

user19161

Or did someone put a virus on my computer?

user19161

Or have I gone nuts?

Charlie

@JasperLoy sent

Dominic Michaelis

@jasperLoy the only expert here is anon or ? :D

user19161

@DominicMichaelis I wonder what would have happened if I clicked on it. anon or Dominic, lol.

user19161

5:56 PM

I will try clicking on it if I see it again later.

user19161

It might be an April Fool's joke, lol.

Peter Tamaroff

I am on the verge of downvoting the guy

user19161

I actually want to downvote many answers too, lol.

user19161

I am sure others want to do the same for mine, lol.

Peter Tamaroff

@JasperLoy Let's go out on a downvoting spree.

But I need at least 5 question to downvote.

Else I lose $0\mod 5$ness.

user19161

5:58 PM

@PeterTamaroff Maybe we will do that and then delete our accounts, lol.

Peter Tamaroff

Which is ugly.

Charlie

@JasperLoy I only downvoted once

user19161

Oh guys we are just joking, please don't quote us OK?

user19161

There are many spies reading...

anon

@Charlie actually, you've downvoted precisely twice

Charlie

6:00 PM

@anon whatever, is less than usual

Stop this boring thing, for God's sake

user19161

So I am the only one who saw "Chat with an expert"?

Charlie

Look like children "i have more pokemon cards than you"

anon

Nah, most of mine are long gone.

Charlie

KNOCK IT OFF, GEEZ!

anon

what are we talking about

Jonas Teuwen

6:03 PM

user19161

@JonasTeuwen Is that your laptop bro?

Jonas Teuwen

That was my little 'proof of concept'. Next up, more space efficient and kinda automatic X-forwarding and stuff.

Charlie

NEVERMIND.

Jonas Teuwen

That's my Chromebook.

@Charlie Do you have Pokemon cards for me?

Charlie

@JonasTeuwen no, I don't, sorry, but I used to have tge pokemons

user19161

6:05 PM

@jonas I think Debian 7 will be released in April.

Jonas Teuwen

@Charlie 8-(.

@JasperLoy Right. This is my own hacked distro.

user19161

@JonasTeuwen It will be the first Debian release with GNOME 3, very exciting...

Jonas Teuwen

(but I use synaptic!)

Desktop managers make my little star itch.

I prefer to manage my own desktop, thanks.

user19161

GNOME 3 is lovely.

Jonas Teuwen

Such bloated product.

Window manager ~5000 SLOC. Perfect.

user19161

6:08 PM

Happy Easter @argon!

Jonas Teuwen

All this library abstraction is zum kotzen.

Argon

@JasperLoy You too, Jasper!

Jonas Teuwen

Anyway. Need food. Will try to find. Damn Easter!

Dominic Michaelis

zum kotzen? are you german ? :D

user19161

@JonasTeuwen Bon appetit!

user19161

6:15 PM

Guys, I saw the "Chat with an expert" again!

user19161

Why don't you guys click on it and see for yourself what happens?

user19161

I have done so, and stopped at some point, and still not sure what's going on...

user19161

I think it might be an April Fool.

pen

@Jasper Just wanted to say, I like how you neatly write the expression on the top line and then simplify it step-by-step on each line.

user19161

@pen Yes, wassup?

Argon

6:23 PM

Bleh, I hate how tedious rational root theorem can get

user19161

@pen I use a mixture of LaTeX and the formatting the site offers. In a purely LaTeX document, things will be different.

user19161

Writing multiline equations in LaTeX is a headache.

pen

I mean that

2 + 2 x 3
= 2 + 6
= 8

will look better than

2 + 2x3 = 2 + 6 = 8

user19161

For a full treatment, consult the standard LaTeX books!

user19161

Well, if it is very short, I write everything in one line here.

user19161

6:25 PM

But if it gets long, I need to break it up.

pen

Yeah, I like the chunks.

That proof you did with ring axioms is neat.

Dominic Michaelis

6:42 PM

@pen you first line is very unusual

it is more \begin{align*} 2 + 2\cdot 3 &= 2 +6 \\ &= 8 \end{align*}

still the left hand side is to long the right hand sides are to short

Git Gud

What are people taking about here? I don't get it: $0+0+0+1=1$.

Dominic Michaelis

@PeterTamaroff your list has some mistakes

april fools

look at the tag

Git Gud

@DominicMichaelis I saw it, but people are commenting some stuff which I don't understand. Are they all joking?

Dominic Michaelis

jupp

Git Gud

Even as a joke I don't understand the first comment.

How does $x=0+0+0+1\Longrightarrow -x=1+0+0+0$?

Dominic Michaelis

6:56 PM

mh left inverse maybe ? don't know

user19161

@GitGud I have downvoted the question and also deletevoted.

math101

7:25 PM

Heyyyyyy

κρανίοπεριπολία

hi

math101

wassup?

κρανίοπεριπολία

Chillin', how 'bout you?

math101

Chillin toooo

κρανίοπεριπολία

cooool

Hi @Charlie @JasperLoy

How are you guys doing?

...

..

.

$\Huge\text\{:-(}$

$\Huge\text{>8(}$

Peter Tamaroff

8:01 PM

@DominicMichaelis what are you talking about?

Dominic Michaelis

@peterTamaroff they list \bot under binary operators

in your latex symbols list

Peter Tamaroff

@DominicMichaelis OK, what's with it?

$\bot$

Dominic Michaelis

but \bot is a mathord not a binary operator, the binary operator is \perp

Peter Tamaroff

$\perp$

Potato, pohtato.

Dominic Michaelis

look at the difference $a\bot b$ and $a \perp b$

Peter Tamaroff

8:04 PM

@DominicMichaelis Right.

@DominicMichaelis What is a "mathord"?

Dominic Michaelis

its an ordinary atom in a math environment

κρανίοπεριπολία

What is an "atom"?

Dominic Michaelis

the binary operators get an infix spacing when they are inbetween two ordinary atoms

like here a-b $a-b$

Peter Tamaroff

@DominicMichaelis "inflix"?

Dominic Michaelis

when they are just alone they get an ordinary spacing just like $ab$ in here $-a$

@PeterTamaroff infix like prefix or postfix

so there is a difference when you write -2 $-2$ and {}-2 ${}-2$

κρανίοπεριπολία

8:10 PM

are numerals considered "atoms"?

Dominic Michaelis

yeah there are only atoms in LaTeX

κρανίοπεριπολία

so numerals and variables

Dominic Michaelis

there are (at least i know) 3 kinds of atoms in the math environment

the operator atom, the ordinary atom and the binary operator atom

κρανίοπεριπολία

I feel like an atomic physicist :D

Dominic Michaelis

I guess LaTeX is much more complicated :D

κρανίοπεριπολία

8:15 PM

what are grouping symbols called?

Dominic Michaelis

what do you mean with grouping symbols ?

κρανίοπεριπολία

Parentheses, brackets, fraction bar

Those are the simplest ones.

Dominic Michaelis

oh fraction bar will be an operator for sure

you can ask TeX to tell it to you

κρανίοπεριπολία

hi @MattN.

Matt N.

My last question is uncannily popular.

κρανίοπεριπολία

8:21 PM

just like you :D

Matt N.

@JonasTeuwen Are you around?

Dominic Michaelis

8:36 PM

@κρανίοπεριπολία with something like that you can ask TeX do give you all the stuff you want to know

\showboxdepth1
\showboxbreadth100
\tracingonline1

at the begin of your document

and \showlists at the end

then the information will be in the log file

κρανίοπεριπολία

@DominicMichaelis Thank you for responding :-)

Dominic Michaelis

my knowledge is still small but those guys at TeX.SE are genius

Charlie

@κρανίοπεριπολία hi

κρανίοπεριπολία

@Charlie hi, how are you?

Charlie

@κρανίοπεριπολία I'm good, and you?

κρανίοπεριπολία

8:40 PM

@Charlie Fine thanks.

@Charlie I like your black swan.

Charlie

@κρανίοπεριπολία :)

@κρανίοπεριπολία thank you

κρανίοπεριπολία

@Charlie It reminds me of the mortal combat logo from far...

Charlie

MORTAL KOMBAT

κρανίοπεριπολία

MORTAL KOMBAT

Oh? it's facing the other way!

Charlie

@κρανίοπεριπολία I love this game

@κρανίοπεριπολία do you like it?

κρανίοπεριπολία

8:48 PM

@Charlie Sorry, never played...

Charlie

@κρανίοπεριπολία :O

κρανίοπεριπολία

@Charlie I know, I know,... it's on my "things to do list."

Charlie

@κρανίοπεριπολία CHUCKY:WINS! Flawless victory FATALITY!

κρανίοπεριπολία

@Charlie That doesn't stop us from being

Charlie

@κρανίοπεριπολία hahaha

κρανίοπεριπολία

8:56 PM

@Charlie hehehe, hihihi, hohoho, huhuhu, and sometimes hyhyhy.

Charlie

@κρανίοπεριπολία you are being faster now

κρανίοπεριπολία

@Charlie Thanks for noticing.

Charlie

@κρανίοπεριπολία :P

κρανίοπεριπολία

@Charlie :-)

Charlie

@κρανίοπεριπολία :)))

κρανίοπεριπολία

9:00 PM

@Charlie :DDD

Charlie

@κρανίοπεριπολία :*

κρανίοπεριπολία

@Charlie }:-)

@Charlie :*

O:)

afk

Ok

9:10 PM

@Charlie I'm back.

Charlie

:D

Good

:D

;D

};D

O;)

9:15 PM

Awww...nice^

O.o

o.O

@Charlie why O.o ?

why not o.O?

9:19 PM

Meh

pen

Guys, may I ask a question related to Sage?

κρανίοπεριπολία

askaway

pen

Project Euler, 21. Here's my code which takes a bit too long.

sum([(a,b) for a in range(1,10001) for b in range(1,10001) if sum(divisors(a)) - a == sum(divisors(b)) - b])

I think there's something wrong here.

Maybe I should first find (a,b), add them to a list and then find the sum of that list.

Jorge Fernández

what is the part of math you like the most?

Dominic Michaelis

@pen what are you doing you need sum(divisors(a))==sum(divisors(b)) && a!=b

pen

9:29 PM

@DominicMichaelis But actually it demands the sum of proper divisors.

Why the second condition?

Charlie

Hi @jasper

user19161

2

Q: What was that? Chat with an "expert"

Today half an hour ago I visited MSE and I was proposed to chat with an "expert". I tried to discuss some questions about von Neumann algebras that botherd me, but this was not an expert I needed. This was not an expert at all and I think this was just a bot. But why is it here?

discussion chat

pen

I want to chat with an expert!

@Jasper Where did you chat with the machine?

Dominic Michaelis

oh divisors gives the trivial too ? sry didn't know that, the second one you need cause the problems say so

user19161

@pen You need to wait for it to appear, just hang around the main site.

pen

9:33 PM

@Dominic Since I am new to programming, can you explain what you mean by a! == b? Is it that you mean that they are symmetric/complementary?

not a == b.

@Jasper Where do they propose you?

Dominic Michaelis

a!=b means $a\neq b$

user19161

@pen It appears as a black box randomly on the main site. If you are lucky you will see it...

pen

@DominicMichaelis lol oh, didn't think of it that way. I always prefer a != b

Will my final code be this?

sum((a,b) for a in range(1,10001) for b in range(1,10001) if sum(divisors(a)) - a == sum(divisors(b)) - b) and a != b)

Dominic Michaelis

i thought i write this ? && is the logical and in mathematica sry i am only used to the mathematica syntax

pen

@DominicMichaelis Yeah, that's fine.

user19161

9:36 PM

@Charlie Hi!

user19161

@κρανίοπεριπολία Hi! Askaway is your pet phrase, lol.

Dominic Michaelis

at first your range is to wide, and you count everything 2 times

κρανίοπεριπολία

@JasperLoy Hi! You don't like it?

pen

@DominicMichaelis Yup. :-\

user19161

@κρανίοπεριπολία No, it's FUN.

pen

9:38 PM

My code is still not working

Jonas Teuwen

@MattN. Yea.. was programming.

pen

lol

I got the black box

Dominic Michaelis

i don't unterstand you if command to be honest, normaly there is if condition , when its true, when its wrong

pen

Look at the picture of that expert.

gyazo.com/652481fbdb5f0ea6683b41870f105d03.png?1364766025

Charlie

@JasperLoy :)

Jonas Teuwen

9:41 PM

Baza!

(My Chromebook)

(With X-Forwarding on the left)

Dominic Michaelis

@pen and even if your code works it will be pretty timeconsuming i think

pen

@DominicMichaelis What'd the correct code be?

Dominic Michaelis

i solved it long time ago with mathematica let me thing about it

programming language sage?

Ok here is mine with mathematica s = 0;
For[i = 100, i < 10000, i++,
If[Plus @@ Delete[Divisors[Plus @@ Delete[Divisors[i], {-1}]], {-1}] == i,
s += i]];
Print[s - 8128 - 496]

took 0.625 seconds

pen

Hmm

Dominic Michaelis

9:57 PM

sage is not so common on project euler ?

i am searching int the forum for it but well don't find something till now

Transcript for

$Mathematics$ Mathematics