Mathematics - 2013-02-17 (page 5 of 5)

Peter Tamaroff

22:01

@DominicMichaelis What do you do?

Dominic Michaelis

i am writing a comment at juliens comment

i think sometimes it is good if you take the to complicated (well in fact it'S only calculating) way

if you don't you never learn to love the elegant ways

user19161

@DominicMichaelis It is more fun to post than to moderate. In another room, they call the mods janitors because they have to clean up the site!

Dominic Michaelis

@peter i would just calculate the determinant of the matrix: D

you think its worth posting it ?

user19161

@amwhy I thought you were going to send me an email this weekend?

Dominic Michaelis

where i live he (she) stilll have 45 minutes

user19161

22:14

@ethan I thought you were going to email me too?

amWhy

Yeah...I hope to yet...

libjup

@DominicMichaelis you still here :) ?

Dominic Michaelis

@libjup again ^^

Peter Tamaroff

@DominicMichaelis Well, it urges for some explanation..

libjup

hard-working guy :)

you helped me with a vector problem today...
"evaluating the norm gives us the distance from the line is sqrt( 5+9 l^2 +12 l
)"
what did you mean with that?

Dominic Michaelis

22:18

@libjup i know

the distance is sqrt(a^2 +b^2+c^2

@peter well det is antisymmetrical that should do it shouldn't it ?

@lib in our case sqrt( (a-b)^2+ (c-d)^2+(e-f)^2)

libjup

yeah sure; but how did you get from
line : x = (1|2|4) + l * (-2|2|1)
and point Q = (8/3 | 4/3 | 8/3)
TO sqrt( 5+9 l^2 +12 l)

Peter Tamaroff

@DominicMichaelis I mean, calculating the determinant is justified with knowledge about systems of linear equations and wether they have or not solutions, which is revelealed by the determinant of the matrix of the system.

Dominic Michaelis

@libjup i calculate sqrt ( (1-2*l -8/3)^2 + (2+2 * l -4/3)^2 + (4+ 1 * l -8/3)^2) and simplified that

libjup

what did you do there? i mean why did you add (-2) to 1 but subtracted 8/3 again? what is this sqrt() the distance to where?

Dominic Michaelis

the l is still there

libjup

22:25

yeah sry

forgot that

Dominic Michaelis

1-2l is the x coordinate of your line

and 8/3 is the x coordinate of your point

libjup

which x-coordinate of my line? i mean my line has endless many x-coordinates ?

sry if I'm kinda slow ^^

Dominic Michaelis

the one with the related l value

my idea is i find a formula for the distance from any point of the line to your point

and minimize this function

libjup

hey! i see the idea :) but (last question): how did you get from the sqrt to 18 l - 12 = 0 ??

Dominic Michaelis

you can ask more questions, i use that the square root is monotone

so if x> y than sqrt(x)> sqrt(y)

you know how to derivative ?

libjup

22:30

yes

you were checking for the slope?

Dominic Michaelis

ok so i say the distance is minimal if the argument of the root

wait let me check up what slope means

yeah i take the derivative to see where the minimum is

at the minimum the derivative must be 0

libjup

so the line is a horizontal?

Dominic Michaelis

i think you mean the right

libjup

ok great!

@DominicMichaelis I think I finally got it

thank you so much ;-) you really helped me

Peter Tamaroff

@JacobBlack Could you help me with the class equation?

Dominic Michaelis

22:34

ok maybe there is an easier way but that was my first thought

libjup

as long as it's correct and a (now) know how it works... I guess it's alright

anyways... have a nice day! I'm sure I'll see you soon again on SO chat ;-)

thanks again

Dominic Michaelis

you are welcome

N3buchadnezzar

Heya!

Dominic Michaelis

hi

N3buchadnezzar

Anyone familiar with maple? Trying to get a good plot of a function that blows up on origo..

mick

22:49

@N3buchadnezzar increase numpoint perhaps ?

@Charlie hi!

I completed my profile today.

lol funny stuff starred

N3buchadnezzar

The only problem is that maple gives some absurd z values for the plot

eg the function mostly lies in the range z = 0 .. 1, but like I said, it blows up at origo..
So the plot looks like a single spike

restart:
with(plots):
plot3d(log(1 + 1/(x^2+y^2) ),x=-1..1,y=-1..1)

mick

you can use the command avoid I think @N3buchadnezzar

draks ...

Hi...

mick

@draks... Hi!

@Charlie you sleeping ?

draks ...

whatssup?

mick

22:54

I completed my profile.

draks ...

very good, you chat profile is missing something in the "about" field...

mick

I starred rob johns comment.

hehe , no its not :)

its a joke

read closely

draks ...

I meant this one : chat.stackexchange.com/users/48741/mick

@Charlie very nice

@mick the orphaned one?

mick

yes.
Btw did you get the joke ?

draks ...

the (my about me is currently blank) one?

mick

22:59

yes

draks ...

hmm, maybe not, if it's a play on words I don't get it, otherwise...

mick

it originally says (your about me is currently blank) :p

draks ...

ahh very nice

mick

@draks...

Dominic Michaelis

mh 24 + till now lets see wheter i get another one for my badge

draks ...

23:01

@mick twitter says your name can "not be empty"

mick

@draks... dunno dont use twitter ...

draks ...

@mick I tried without success

mick

lol you tried "empty" ? @draks...

draks ...

in fact "not be empty"

mick

I posted a new question today ...

draks ...

23:03

which one?

mick

my latest one :p see profile

@draks...

draks ...

nice, I like primes...

mick

good , now give a good answer :) @draks...

draks ...

I give an intersting link instead: en.wikipedia.org/wiki/List_of_prime_numbers

mick

I believe it is death star at your avatar not ? @draks...

Dominic Michaelis

23:05

"This is an incomplete list" lol

draks ...

it was, now it's mimas

one of jupiter's moons

mick

@draks... I hope that was a joke and im not suppose to find a usefull pattern

like a triple nested selfreferenced recursion or such :)

@Charlie you busy or sleeping ?

Dominic Michaelis

ever tried googling recursion ?

draks ...

@mick the "centered" ones could of interest to you

Peter Tamaroff

@julien

mick

23:11

@DominicMichaelis yes why ?

Peter Tamaroff

@amWhy Do you think you can help me with some group theory?

mick

@Ethereal hi and bye :)

draks ...

bye @mick

mick

bye@draks...

Dominic Michaelis

there is a easter egg ^^

mick

23:13

bye everyone

@DominicMichaelis ?

Dominic Michaelis

if you google recursion

it tells you

"did you mean recursion"

mick

oh yes i know

draks ...

@DominicMichaelis hahaha

mick

bye@Charlie

draks ...

@PeterTamaroff Hi, YOU need help with some group theory? Wow, would you mind sharing the problem?

Charlie

23:20

@mick I'm so sorry, I was afk, terribly sorry!!!!:(

@draks... :P

@draks wie gehts?

draks ...

@Charlie danke gut und dir? Wart' mal ich hol mir noch ein Bier...

Charlie

@draks... nein sehr gut

is it right?*

draks ...

perfect...

Charlie

@draks... really?

draks ...

@Charlie ja

Charlie

23:28

@draks... :D

draks ...

and why do you feel like that?

Charlie

@draks... ahh....boredom

lack of enthusiasm

draks ...

for what?

Charlie

many things

N3buchadnezzar

Hmm is there any compact way to write $x \in [-1,1],\ y \in [-1,1]$ ?

draks ...

23:31

$x,y\in[-1,1]$

N3buchadnezzar

$f \in [-1,1]\times[-1,1]$ ?

draks ...

call $x=x_1$ and $y=x_2$ then $x_k\in[-1,1]$

@Charlie some music?

Charlie

@draks... you mean if i want some music?

draks ...

yes here you go...

►

Charlie

@draks... this is a motherfuckin cool song

draks ...

23:37

@Charlie I just bought the Star Wars Suite

Charlie

If I were Darth Vader, I would choke many people

@draks... really?????????

draks ...

and it's so cool to listen to it while driving

@Charlie hey don't let the drak side catch you...

Charlie

@draks... haha

@draks... walking!

draks ...

@Charlie Whenever I'm in an elevator a start whistling the Imperial March...

Charlie

@draks... nice!

►

draks ...

23:40

gotta change the avatar back, I think...

Charlie

@draks... you know about sw 7?

draks ...

I heard that they plan to make it

and I fear it...

Charlie

@draks... jj abrams is the director

draks ...

is that a good sign?

Charlie

@draks... i'll eat brb

draks ...

23:42

but we'll watch it, don't we?

try this:

►

@Charlie hey sorry I gotta go, but...

May the force be with you!

3

Transcript for

$Mathematics$ Mathematics