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Matt N.
Matt N.
9:11 AM
@robjohn I still visit his profile once a day. I can't help it. : (
 
robjohn
robjohn
@MattN. why can't you visit here if t.b. is not here?
 
Matt N.
Matt N.
9:25 AM
@robjohn I can. And I do. But I have not much motivation to visit. Why?
 
robjohn
robjohn
@MattN. It's just that each time I talk to you, it seems to be about him. I'm sure he will be back, though I don't know when.
 
Matt N.
Matt N.
@robjohn Sorry about that.
Will stop now.
But I think "gone" is pretty clear. I don't think he'll be back.
 
robjohn
robjohn
@MattN. You don't need to. I was just wondering if you had anything about math you wanted to talk about :-)
 
Matt N.
Matt N.
@robjohn To you? Or in general? I'm about to post a reply to Old John about a puzzle thingie.
 
skullpatrol
skullpatrol
I have something about math I'd like to talk about... why is it so hard?
:-D
 
Matt N.
Matt N.
9:31 AM
@OldJohn I did some more. Let the board have dimension $n \times m$. Assuming that the conjecture is that it works if at least one of them is even and that it doesn't work if both are odd, assume both are odd. Then I computed total number of blacks = $\frac{mn + 1}{1}$ and total number of whites = $\frac{nm - 1}{2}$.
 
robjohn
robjohn
@MattN. Ah, good :-) I just didn't want to think that you were only here to look for t.b.
 
Matt N.
Matt N.
@robjohn Oh no : ) I'm only here to complain about his absence : D
 
N3buchadnezzar
N3buchadnezzar
@robjohn You can always help me with linear algebra ^^
 
Matt N.
Matt N.
Joking. But it's as if I lost all the fun. I had one last lolz though: I edited some of my old questions so that now he's got an abstract-algebra badge : D (he wouldn't miss a chance to point out how he didn't know and did not like algebra)
Ok. Going to do some more stuff now! See you later! : )
 
robjohn
robjohn
@MattN. hurry back!
 
skullpatrol
skullpatrol
9:36 AM
@robjohn Tough love?
 
robjohn
robjohn
@N3buchadnezzar What's bugging you about Linear Algebra these days?
 
N3buchadnezzar
N3buchadnezzar
Everythng!
I have a hand in that I can not wrap my head around, I find every question very hard. It is quite discouraging.
 
skullpatrol
skullpatrol
1 hour ago, by N3buchadnezzar
bleh http://www.math.ntnu.no/emner/TMA4145/2012h/exercises/oving7.pdf
 
Rajesh D
Rajesh D
@N3bu : Why not grab hold of video lectures by Gilbert Strang at MIT courseware
 
robjohn
robjohn
@RajeshD tab completion :-)
 
Rajesh D
Rajesh D
9:54 AM
@robjohn thanks @robjohn I knew this in linux but didn't know it works here.
:-)
 
robjohn
robjohn
@RajeshD I think it's easier to type`@n3<tab>`
 
Rajesh D
Rajesh D
yes agree
wasn't aware, I was switching to mouse to autocomplete which wasn't of help, tab is good option
@robjohn : BTW I wonder you got any chance to look at the problem I've sent
2:58 AM aw
 
Matt N.
Matt N.
@OldJohn I did another one: "A certain square milkcrate can hold 36 bottles of milk. Can you arrange 14 bottles in the crate so that each row and each column has an even number of bottles?
I think the answer is that we have to place them in blocks of 4. And 14 isn't divisible by 4. So the answer is no.
This argument also applies to crates of arbitrary dimension. What do you think of this?
(I guess one would have to formally prove it.)
 
Bitrex
Bitrex
Beer crate - only prove it if it's a crate of beer
 
Jayesh Badwaik
Jayesh Badwaik
10:19 AM
 
Old John
Old John
10:48 AM
@MattN. Not sure about the milk crate (I will try to have a look at it later)
The state-of-play on the coins is this:
If at least one dimension is even then it is possible (proved)
If both are odd and you start on a white, then it is impossible (proved)
If both odd and you start on black then it is possible (not yet proved)
 
skullpatrol
skullpatrol
@OldJohn Would a three dimensional version of this puzzle be much harder to prove?
A 5 X 5 X 5 cube?
 
Old John
Old John
@skullpatrol That might be possible using pretty much the same argument - but I am not sure yet ...
@MattN. I am not convinced your argument about divisibility by 4 works: I can manage to put 4, 6, 8, or 10 bottles in there with even in each row and colum
(assuming 0 counts as even)
 
Jayesh Badwaik
Jayesh Badwaik
@OldJohn Yes it does!
 
Old John
Old John
@JayeshBadwaik good :)
 
skullpatrol
skullpatrol
11:04 AM
@OldJohn Have you done any work with hypercubes?
 
Old John
Old John
@skullpatrol Not serious work - but I have played with them in the past
 
skullpatrol
skullpatrol
user image
2
 
Old John
Old John
@skullpatrol That is lovely - and very helpful for trying to visualise what goes on in 4 dimensions
I spent quite a lot of time years ago trying to visualise several aspects of 4-dim, and managed to get a reasonable understanding of some aspects, but struggled with knotting surfaces in 4-dim
 
skullpatrol
skullpatrol
o_0
 
Jayesh Badwaik
Jayesh Badwaik
Now I get it! "The above illustration" @skullpatrol its really good :-)
 
skullpatrol
skullpatrol
11:20 AM
Wolfram has an interactive display
 
Old John
Old John
@JayeshBadwaik You need to compare that rotating hypercube with a similar version of rotating a 3-d cube to get a good idea of what is going on. If you rotate a 3-d cube, the square faces appear as parallelograms which change shape as the cube rotates - in the same way that the cubes in your animation appear to distort as it rotates.
 
Jayesh Badwaik
Jayesh Badwaik
11:38 AM
@OldJohn Thanks.
@skullpatrol thank you.
 
skullpatrol
skullpatrol
np
 
Matt N.
Matt N.
@OldJohn Can you show me the pattern when you place 6?
 
Jayesh Badwaik
Jayesh Badwaik
o # #
# # o
# o #
 
Old John
Old John
1 and 2 on top row
1 and 3 on second row
2 and 3 on 3rd row
so there are either 2 or 0 in each row and each column
 
Matt N.
Matt N.
@OldJohn It works. Hah. 0_0
You broke my answer :,(
(joking : ) Thanks a lot!)
 
Old John
Old John
11:53 AM
sorry!!!
2 and 14 seem to be the ones that fail - and I can't see why ... yet
(apart from an odd number of bottles - but they obviously fail)
 
Matt N.
Matt N.
Well. Isn't 2 "obvious", too?
 
Old John
Old John
It is
 
Matt N.
Matt N.
Maybe the true statement would be either place them in blocks of 4 or pairs of 3? 
Like
      . .
      .   .
        . .
 
Old John
Old John
It might be that it is possible for any even number apart from those equiv to 2 mod 12 ... no idea really, though
 
Matt N.
Matt N.
I think I'll leave it at that for now. The next puzzle in the book is the chess board tiling with dominoes after removing two corners : )
I'll be back later! : )
 
Old John
Old John
11:58 AM
@MattN. that is the one that gave me the idea for the coins proof :)
speak later
 
Jayesh Badwaik
Jayesh Badwaik
0 0 0 0 0 0
0 0 0 0 # #
0 # # 0 # #
# # 0 0 0 0
# 0 # 0 # #
0 0 0 0 # #
@OldJohn Is the above correct?
 
Old John
Old John
@JayeshBadwaik looks correct to me! - so 14 is possible after all :)
 
Jayesh Badwaik
Jayesh Badwaik
@OldJohn good. :-)
 
Old John
Old John
@JayeshBadwaik well done
 
skullpatrol
skullpatrol
hi @Charlie
 
Jayesh Badwaik
Jayesh Badwaik
12:04 PM
@OldJohn thank you. :-)
 
Old John
Old John
@JayeshBadwaik :)
 
Charlie
Charlie
@skullpatrol Hello,Skull!wassup!
 
skullpatrol
skullpatrol
@Charlie not much, you?
 
Old John
Old John
@JayeshBadwaik You have saved me from wasting an hour or two trying to prove it impossible :)
 
Charlie
Charlie
@skullpatrol good.
 
Jayesh Badwaik
Jayesh Badwaik
12:05 PM
@OldJohn Nice. Finally I am useful. :-)
 
Old John
Old John
@JayeshBadwaik I never doubted it!
 
Charlie
Charlie
@JayeshBadwaik I always said you were!
You are.
 
Jayesh Badwaik
Jayesh Badwaik
@OldJohn Good. :-) To take it farther from here. A good approach might be to write any even number as $4x + 6y + 10y + \cdots$ and then try to divide any given square into disjoint dominoes of $2 \times 2$ and $3 \times 3$ and similarlly.
 
Old John
Old John
@JayeshBadwaik Good approach - and every even number above 2 can certainly be written in that form :)
 
Jayesh Badwaik
Jayesh Badwaik
@OldJohn I edited my comment I mean, that is one approach, but we can probably have multiple approaches.
 
Old John
Old John
12:09 PM
the only problem is the limitations of the size of the crate
 
Jayesh Badwaik
Jayesh Badwaik
@Charlie :-)
@OldJohn Yes.
 
Sanjay dev
Sanjay dev
:-)
 
Jayesh Badwaik
Jayesh Badwaik
@Sanjaydev Good evening.
 
Old John
Old John
If we have a big enough crate. I think that every even number bigger than 2 should be possible with your idea
 
Sanjay dev
Sanjay dev
@j
thanks
 
Charlie
Charlie
12:11 PM
@JayeshBadwaik How are you?
 
Jayesh Badwaik
Jayesh Badwaik
@OldJohn I think one can always use my first approach if $n^2 > \frac{3}{2} k$
where k is the number of bottles, and $n$ is the square crate.
 
Old John
Old John
@JayeshBadwaik Hmm - not totally sure ...
 
Jayesh Badwaik
Jayesh Badwaik
@Charlie Better.
@OldJohn Yeah. Not sure. Will try to work on it later.
 
Old John
Old John
can you be certain there will always be room to fit in all the blocks without them overlapping?
 
Charlie
Charlie
@JayeshBadwaik :-D
 
Old John
Old John
12:13 PM
@JayeshBadwaik but the important thing is that we (you!) have settled Matt's problem
 
Jayesh Badwaik
Jayesh Badwaik
@OldJohn Yup. :-)
@Charlie :-D
 
Charlie
Charlie
@JayeshBadwaik so the problem is solved?
 
Jayesh Badwaik
Jayesh Badwaik
@Charlie Matt's problem? Yes.
 
Charlie
Charlie
12:29 PM
@JayeshBadwaik Hooray!
 
Jayesh Badwaik
Jayesh Badwaik
@Charlie :-)
 
Charlie
Charlie
:-D
@JayeshBadwaik if i tellya something you promise you won't laugh?
 
Jayesh Badwaik
Jayesh Badwaik
@Charlie I won't.
 
Charlie
Charlie
@JayeshBadwaik So..in my january vacation i was trying to make a project... i would ask for help to my prof... but then i gave up because i thought they would mock me.I would to make a project to build a tricorder...
 
Matt N.
Matt N.
I know : ) (they should rearrange the book so that the chessboard one comes before the coins one). I think I have it. What do think of this: if $n$ is even there are
$$ \tt{black} = \frac{n^2}{2} = \tt{white}$$
If $n$ is odd there are
$$ \tt{black} = \frac{n^2 +1}{2}$$
$$ \tt{white} = \frac{n^2 - 1}{2}$$

So if $n$ is even and we remove $2$ from an $n \times n$ board the remaining numbers are
$$ \tt{black} = n^2 / 2 - 2$$
$$ \tt{white} = n^2 / 2$$
Since we cover white and black in pairs we see that we cannot cover the board. In fact, even if we remove just one square, black or white, we can…
 
Old John
Old John
12:36 PM
@MattN. Yep - agreed
wait - when you say "remove 2" - I think you mean to say"If we remove 2 of the same colour..."
 
Matt N.
Matt N.
Similarly, if $n$ is odd we have (after removing 2 black ones)
$$ \tt{black} = \frac{n^2 + 1}{2} - 2$$
$$ \tt{white} = \frac{n^2 -1}{2}$$
and again we see that we cannot cover the board.
@OldJohn Yes!
@OldJohn What I don't understand is, why they have to be diagonally opposite corners. It seems that the argument works for any two of the same colour in the odd case and for any one square in the even case.
 
Old John
Old John
for the domino problem we don't even need to consider colours when we have odd x odd, as the number of squares is odd and cannot be covered by dominoes as they cover 2 squares each :)
 
Matt N.
Matt N.
@OldJohn True! : D
I guess it's to distract and confuse the reader.
 
Old John
Old John
@MattN. the reason they specify opposite corners is just a way of getting 2 of the same colour removed, without mentioning colours (as that might give the game away!)
 
Matt N.
Matt N.
Or that : )
 
Jayesh Badwaik
Jayesh Badwaik
12:41 PM
@Charlie Wouldn't tricorder be too complex to make?
 
Matt N.
Matt N.
@OldJohn Ok, I'll bbl! : )
 
Charlie
Charlie
@JayeshBadwaik I know...that's why i said you couldn't laugh...
but it is reality
 
Jayesh Badwaik
Jayesh Badwaik
@Charlie Hmm. You can always try though. You might get at least some small thing made, which would be a good achievement in itself.
I believe the smartphones are the tricorders of today.
 
Charlie
Charlie
:D did you watch Prometheus?
so there's a machine that makes surgeries.REally awesome.it gives ideas, Jay.
 
Jayesh Badwaik
Jayesh Badwaik
You mean the film?
Haven't seen it yet.
 
Charlie
Charlie
12:48 PM
@JayeshBadwaik I liked it!
 
Jayesh Badwaik
Jayesh Badwaik
@Charlie okay!
 
Charlie
Charlie
:D
 
skullpatrol
skullpatrol
@Charlie Do you mind if I ask you why you don't always put spaces between your words?
 
Old John
Old John
@skullpatrol I have a keyboard that does that to me toosometimes :)
2
 
Charlie
Charlie
@skullpatrol oh... my space bar ..you have to hit it strong...
 
skullpatrol
skullpatrol
12:55 PM
OK :)
I thought there was some metaphorical reason...
 
Charlie
Charlie
no no
@Jayesh I'm feeling a little guilty for your lack of sleep...
 
Jayesh Badwaik
Jayesh Badwaik
1:21 PM
@Charlie Bleh. What? I am perfectly fine!
 
Charlie
Charlie
@JayeshBadwaik Really?You swear?
 
Jayesh Badwaik
Jayesh Badwaik
@Charlie I swear.
 
Charlie
Charlie
@JayeshBadwaik :-D
Kow what's my fav Beatles song?
 
Jayesh Badwaik
Jayesh Badwaik
Naah.
 
Charlie
Charlie
Hello ,Goodbye
'twas the first english song I learned in english class
 
Jayesh Badwaik
Jayesh Badwaik
1:26 PM
Hmm.
 
Charlie
Charlie
I don't why you say goodbye I say hello
@JayeshBadwaik what about you?
 
Jayesh Badwaik
Jayesh Badwaik
@Charlie Here comes the sun.
 
Charlie
Charlie
\o/
doodoodoodoo
 
Khromonkey
Khromonkey
How can i find the integral of $\sqrt{r^2-x^2}$
 
Charlie
Charlie
@JayeshBadwaik And I say :It's alright!
 
Jayesh Badwaik
Jayesh Badwaik
1:31 PM
@Charlie hehe,
 
Khromonkey
Khromonkey
I want to find formula for area of circle
 
Charlie
Charlie
you will find the area of a half of it
@JayeshBadwaik I like when you understand what I say.LIke yesterday with Penny Lane!
 
Jayesh Badwaik
Jayesh Badwaik
@Charlie Yup, Me too.
@Charlie Might go out in a bit for some groceries and dinner.
So, bye for now. BBL.
 
Charlie
Charlie
@JayeshBadwaik OK.:)
 
Jayesh Badwaik
Jayesh Badwaik
2:25 PM
 
Charlie
Charlie
@JayeshBadwaik oh, darling...what is XML?sorry to ask...
got it
feel so dumb when I dunno these things...
 
anon
anon
Are quotients by conjugate subgroups isomorphic as $G$-spaces (i.e. does $H\sim K$ imply there is a $G$-equivariant bijection between the quotient sets $G/H$ and $G/K$)? My first guess was that they would be, but I don't immediately see an isomorphism.
 
Old John
Old John
2:40 PM
@anon I don't see an obvious one - which might make me start to look for a counter-example
(but I am not an algebraist!)
 
user19161
2:56 PM
@JayeshBadwaik Ah, I never read these security bulletins. Risks are always there.
 
Jayesh Badwaik
Jayesh Badwaik
@JasperLoy Some are greater than others!
 
Rajesh D
Rajesh D
Hi @robjohn
 
robjohn
robjohn
@RajeshD hey there
 
Rajesh D
Rajesh D
@robjohn about the problem
ok
 
Charlie
Charlie
3:18 PM
@JasperLoy Hello!!!!!!!!!!!!!!!!!!
 
user19161
3:33 PM
@Charlie It must be lunch time now there.
 
Charlie
Charlie
@JasperLoy there where?
 
user19161
@Charlie You.
 
Charlie
Charlie
@JasperLoy oh yeah. i already had my lunch.:-D
@Jas are you there?
 
Charlie
Charlie
3:50 PM
@MohamedAhmedNabil How are you?Hello!
 
Mohamed Ahmed Nabil
Mohamed Ahmed Nabil
@Charlie hi :D im fine, what about you?
 
Charlie
Charlie
@MohamedAhmedNabil Good!
@MohamedAhmedNabil studying?
 
Mohamed Ahmed Nabil
Mohamed Ahmed Nabil
@Charlie It's Thursday, My Rest Day :D
 
Old John
Old John
@MohamedAhmedNabil Ahlan wa sahlan :)
 
Mohamed Ahmed Nabil
Mohamed Ahmed Nabil
@OldJohn Ahlan :D
 
Charlie
Charlie
3:53 PM
@MohamedAhmedNabil that's good!
 
Old John
Old John
is it ahlan? 2ahlan? 3ahlan? (not got the hang of it all yet!
 
Mohamed Ahmed Nabil
Mohamed Ahmed Nabil
@OldJohn ahlan or 2ahlan doesnt really matter. This is franco arabic. Whatever sounds right, no rules
 
Old John
Old John
@MohamedAhmedNabil Great :)
 
Mohamed Ahmed Nabil
Mohamed Ahmed Nabil
This is how you set the mood for a Thursday
 
Charlie
Charlie
@MohamedAhmedNabil Nice song!I liked!
 
Mohamed Ahmed Nabil
Mohamed Ahmed Nabil
3:57 PM
Anyone else starts his week on Sunday and ends on Thursday?
 
Old John
Old John
@MohamedAhmedNabil Only when I am in Abu Dhabi :)
 
Charlie
Charlie
O.o
 
Mohamed Ahmed Nabil
Mohamed Ahmed Nabil
@OldJohn I thought they started Staturday there
 
Old John
Old John
@MohamedAhmedNabil Maybe - but the people I visit there do bot work on Saturday - so they consider the week starting on Sunday
 
Mohamed Ahmed Nabil
Mohamed Ahmed Nabil
Installing windows 7 in Virtual Box, Hope this works ^.^
 
Old John
Old John
4:03 PM
@MohamedAhmedNabil should be fine - I have always had good results with virtual Box
 
Mohamed Ahmed Nabil
Mohamed Ahmed Nabil
@OldJohn whats your os?
 
Old John
Old John
I always use Linux now - Mint / Debian / Slackware
 
Mohamed Ahmed Nabil
Mohamed Ahmed Nabil
@OldJohn Ubuntu here :D
 
Old John
Old John
@MohamedAhmedNabil I have used Ubuntu - but switched when they started changing the interface - although I used Xubuntu for a while
I quite like small and fast window managers :)
 
Mohamed Ahmed Nabil
Mohamed Ahmed Nabil
@OldJohn but unity is amazing
 
Old John
Old John
4:08 PM
@MohamedAhmedNabil Hmm - I didn't like it so much
 
Mohamed Ahmed Nabil
Mohamed Ahmed Nabil
@OldJohn you should check ubuntu 12.04
 
Old John
Old John
Maybe I will try it in a VM :)
I guess 12.10 will be out soon?
 
Mohamed Ahmed Nabil
Mohamed Ahmed Nabil
@OldJohn yea I think so
@OldJohn Changing from windows to ubuntu was an amazing change :D
 
Old John
Old John
I also want to give ArchLinux a try - some people here use it
@MohamedAhmedNabil I first started using Slackware back in about 1995-ish and it was a tough transition in those days
 
Mohamed Ahmed Nabil
Mohamed Ahmed Nabil
@OldJohn Im using virtual box to run a game, Is there a better option?
 
Old John
Old John
4:11 PM
@MohamedAhmedNabil I am the worst person to ask about games - I never play them :)
 
Mohamed Ahmed Nabil
Mohamed Ahmed Nabil
@OldJohn Is virtual box laggy?
 
Matt N.
Matt N.
@OldJohn I just did another one. This one was one of the very few puzzles I enjoyed solving : )
 
Old John
Old John
It must have some lag - but not sure if it is very noticeable
@MattN. Nice - and I would put money on that being the correct approach
+1
 
Matt N.
Matt N.
@OldJohn Nice : D But wait with the money! I'm not too sure I got it right.
And thanks.
 
Old John
Old John
I'm sure - it cannot be wrong :)
 
Matt N.
Matt N.
4:15 PM
: O
How can you be sure?
 
Old John
Old John
before I read your answer, I got the same answer with the gcd in it (but I hadn't got as far as using the subgroup process)
 
Matt N.
Matt N.
Nice : )
Particularly pleasing cause my group theory is shaky.
 
Old John
Old John
My mind works in a very geometrical way, and I "solved" it very quickly as a mental image - I often do that - but then spend ages writing out a sensible proof - like with the coins thing yesterday :)
 
Matt N.
Matt N.
Yeah, it took me two examples to figure it out (my suspicion) and then about half an hour to come up with the "why", that is, the groups thing.
 
Old John
Old John
@MattN. I find it hardest when I have a geometric solution, but no real mathematical structure (group / ring etc.) then it can be hard to explain in words (at least for me)
some of my favourite proofs are ones with no words - like the geometric proof that the sum of the first n cubes equals the square of the sum of the first n integers
 
Matt N.
Matt N.
4:22 PM
@OldJohn I thought one could learn that by practicing! : /
 
Old John
Old John
@MattN. yep - I am better at it now than I used to be
Just got the hang of it at the stage when I am not doing serious maths anymore :O
 
Matt N.
Matt N.
@OldJohn Maths trolling success!
3
: )
 
Jayesh Badwaik
Jayesh Badwaik
@MattN. Really nice question.
 
Matt N.
Matt N.
@JayeshBadwaik Yes, I agree!
 
Charlie
Charlie
where does he take these from?
 
Matt N.
Matt N.
4:27 PM
Going afk for a while.
@Charlie See my profile on the site
 
Jayesh Badwaik
Jayesh Badwaik
@Charlie Alpha is back. (charlie and alpha are popular code names of secret agents)
 
user19161
@Charlie I am here now.
 
user19161
@JayeshBadwaik Who is Alpha?
 
Charlie
Charlie
@MattN. hmm
@JayeshBadwaik hehehe
 
Jayesh Badwaik
Jayesh Badwaik
@JasperLoy See my edited post.
 
Old John
Old John
4:28 PM
@MattN. trolling??
 
Charlie
Charlie
He's back because" we don't say goodbye..." isn't it @jayesh?
 
user19161
Mysterious words again...
 
Charlie
Charlie
@jayesh understood
 
user19161
@MohamedAhmedNabil Sorry, this song sounds really sad.
 
Charlie
Charlie
?
 
Mohamed Ahmed Nabil
Mohamed Ahmed Nabil
4:30 PM
@JasperLoy whoa ??!!
 
Jayesh Badwaik
Jayesh Badwaik
@Charlie Yup. I edited it for jasper.
 
user19161
@MohamedAhmedNabil Well, I just listened to it. It is depressing.
 
Jayesh Badwaik
Jayesh Badwaik
@Charlie Yup.
 
Charlie
Charlie
:-D
 
Mohamed Ahmed Nabil
Mohamed Ahmed Nabil
@JasperLoy but..but..but.. It's Thursday
 
Charlie
Charlie
4:32 PM
@JasperLoy how depressing?
 
Old John
Old John
wow - managed to get a first answer in for a question for a change :)
 
user19161
@MattN. Do you use American or British spelling? If the latter, it should be "practising".
 
Jayesh Badwaik
Jayesh Badwaik
@OldJohn Congratulations!
 
user19161
@Charlie Very. Not my type of music.
 
Charlie
Charlie
:(
 
Old John
Old John
4:33 PM
beat the next answer by a whole minute :)
 
user19161
@OldJohn How much change? Ten cents?
 
Jayesh Badwaik
Jayesh Badwaik
@MohamedAhmedNabil Just because Friday is infinitely more depressing does not mean thursday should be by default cheerful. :P :P (Rhetorical Statement, I did not see that song)
 
Matt N.
Matt N.
@OldJohn Yes. Maths trolled you : )
 
Old John
Old John
@JasperLoy probably what it was worth - a very easy question
 
Jayesh Badwaik
Jayesh Badwaik
@JasperLoy Pennies, Jasper, Pennies.
 
Matt N.
Matt N.
4:34 PM
@JasperLoy Thanks for pointing that out. I consider American English to be typos : )
 
Charlie
Charlie
Up in the sky, you can fly
You will make it if you try
In the sky you are far away
 
Old John
Old John
@MattN. :)
 
user19161
@JayeshBadwaik You misspelled "rhetorical".
 
Mohamed Ahmed Nabil
Mohamed Ahmed Nabil
@JayeshBadwaik Thursday is the Middle Eastern Friday
 
Jayesh Badwaik
Jayesh Badwaik
@JasperLoy Thanks.
 
Matt N.
Matt N.
4:34 PM
Ok. Off to do more recreational maths.
 
Charlie
Charlie
tomorrow is holiday!uhuuu
 
Jayesh Badwaik
Jayesh Badwaik
@MohamedAhmedNabil I know. I live just across the arabian sea. :-)
 
user19161
Like Mariano says, correcting spellings is a great way to make friends online.
 
Charlie
Charlie
@JasperLoy oh yeah
 
Jayesh Badwaik
Jayesh Badwaik
@JasperLoy yup.
 
user19161
4:35 PM
@Charlie I must attribute it to Mariano, in case skull says I omit the attribution.
 
Charlie
Charlie
@JasperLoy Jasper you give me the feeling that people probably had when i stopped their speech only to correct what they said.
it's a good thing, ok?
 
user19161
@Charlie I do it just for fun, not because of other reasons.
 
Charlie
Charlie
@JasperLoy i did it on purpose...
 
Old John
Old John
Interesting concept of "fun"
 
Jayesh Badwaik
Jayesh Badwaik
Low Hanging Fruits do not need motivation based on rewards apparently. For example, normal good questions on ArchLinux Mailing List have one or two response, and LHF's have around 10-12 even though it doesn't really earn you anything, if nothing, generally more questions and answers.
 
user19161
4:38 PM
@OldJohn In case someone thinks that is one of my disorders.
 
Old John
Old John
@JasperLoy as in GND?
 
user19161
@OldJohn Yeah, or an obsession with spelling correction specifically.
 
Old John
Old John
@JasperLoy we all have our obsessions ...
 
user19161
@JayeshBadwaik I think the Arch documentation is very well written.
 
Charlie
Charlie
@JasperLoy I don't think it's a bad thing..unless you do this when i have pms... then i might become a devil
 
Jayesh Badwaik
Jayesh Badwaik
4:40 PM
@JasperLoy Yup. It is one of the best out there.
 
user19161
@JayeshBadwaik Only the Ubuntu site makes instructions for installing so easy. They tell you how to burn the image.
 
Jayesh Badwaik
Jayesh Badwaik
@JasperLoy I haven't used a CD/DVD (any optical disc) in two years. :P
 
user19161
@JayeshBadwaik I now have two rewritable DVDs, one Debian and one TeX Live.
 
Jayesh Badwaik
Jayesh Badwaik
@JasperLoy Hmm.
 
Charlie
Charlie
@jayesh what linear algebra book you used?
 
user19161
4:44 PM
@JayeshBadwaik It is interesting how some distros give you a CD sized image and others much bigger. The bigger ones do not always contain more programs.
 
user19161
@Charlie Most of my courses did not use any specific books, just really lousy notes written by the lecturer or someone else.
 
Jayesh Badwaik
Jayesh Badwaik
@JasperLoy No, only Ubuntu DVD's do not contain more programs, because it contains langpacks. But all other Distro DVD's contain more packages than CDs.
 
Charlie
Charlie
@JasperLoy my prof uses a book i cannot find anywhere....
 
user19161
@JayeshBadwaik Hmm, I was really thinking about how some distros manage to squeeze in many things into a CD.
 
Jayesh Badwaik
Jayesh Badwaik
@Charlie First Strang, then Lang and now will study either Kunze or Roman.
 
user19161
4:46 PM
@Charlie Author?
 
Charlie
Charlie
i'm currently using kunze..but it's not helping
@JasperLoy a brazilian one
 
Jayesh Badwaik
Jayesh Badwaik
@JasperLoy They don't squeeze, they just omit many things which are not used by other people.
@Charlie Is this your first course?
 
user19161
@Charlie A classic, very good. In my list of good books.
 
Mohamed Ahmed Nabil
Mohamed Ahmed Nabil
I got windows 7 on virtual box woooohoooo
 
user19161
I recommend all of you take a look at a new LA book.
 
Charlie
Charlie
4:47 PM
@JayeshBadwaik yup..oh jayesh...his lectures sucks...
 
Mohamed Ahmed Nabil
Mohamed Ahmed Nabil
now how do i transfer files to my virtual machine?
 
user19161
It is Petersen's Linear Algebra.
 
anon
anon
@OldJohn Apparently there is an isomorphism, $aH\mapsto ag^{-1}(gHg^{-1})$.
 
Jayesh Badwaik
Jayesh Badwaik
@MohamedAhmedNabil Hehe, you may be better off asking this on some SE site. It depends a lot on which VM software you are using.
 
Old John
Old John
@anon Darn - there goes my intuition again :)
 
Mohamed Ahmed Nabil
Mohamed Ahmed Nabil
4:49 PM
@JayeshBadwaik probably but I know people here :D
 
Jayesh Badwaik
Jayesh Badwaik
@anon Sorry to interrupt, but what is $H$?
 
Old John
Old John
@anon what exactly is $g$?
 
Charlie
Charlie
@JasperLoy is it good?
 
Mohamed Ahmed Nabil
Mohamed Ahmed Nabil
@OldJohn so how do I get files into a VirtualBox Virtual Machine ? :)
 
Jayesh Badwaik
Jayesh Badwaik
@Charlie Ohh. Then you may be better of studying Lang Linear Algebra.
 
user19161
4:50 PM
@Charlie If I were to get one single linear algebra book not covering anything else, it would be this one.
 
Old John
Old John
@MohamedAhmedNabil you can use sftp, ssh or a shared folder on the host machine
if the guest is windows, then shared folder is easiest
 
Charlie
Charlie
@JayeshBadwaik really?
 
anon
anon
$H$ and $K=gHg^{-1}$ are conjugate subgroups of a group $G$, and the map $aH\mapsto ag^{-1}(gHg^{-1})=aHg^{-1}$ is an isomorphism between $G/H$ and $G/K$ as $G$-spaces (ie a $G$-equivariant bijection between the quotient sets).
 
Jayesh Badwaik
Jayesh Badwaik
@MohamedAhmedNabil You have to modify an option in the VirtualBox. In virtual box, you can share a folder between VMs using an option in the settings. That way, any file you put in that folder would be available to you in the other OS.
 
Old John
Old John
@anon Ah - OK - I didn't know about the conjugate subgroups bit earlier
 
Mohamed Ahmed Nabil
Mohamed Ahmed Nabil
4:51 PM
well, duck the rest of SE. This is the best room <3
 
user19161
@MohamedAhmedNabil Of course. Math people are the most fun people on earth!
4
 
arete
arete
Hey ladies and gents. I've been playing around with fixed point iteration in matlab and I came to a weird conclusion. For the function $x^2+x-2$ the fixed point is $\sqrt{2}$, but when I start the script I wrote, starting at $\sqrt{2}$, it eventually diverges after a few iterations.
 
Mohamed Ahmed Nabil
Mohamed Ahmed Nabil
@JasperLoy duck yea :D
 
Jayesh Badwaik
Jayesh Badwaik
@Charlie I think so. However, get a second opinion from @JasperLoy.
 
Charlie
Charlie
@jas I need a second opinion
 
user19161
4:52 PM
@Charlie And what is the exact question?
 
Jayesh Badwaik
Jayesh Badwaik
@arete There are basins of convergence depending on your method. It is quiet possible, your intial approximation does not lie in that basin.
@JasperLoy I recommended Lang Linear Algebra as the book for the first course in LA.
 
anon
anon
@arete it's possible it's not a stable equilibrium, in which case approximations of the point $\sqrt{2}$ will grow farther away from the point rather than tending toward it.
 
arete
arete
Is this due to the irrationality of $\sqrt{2}$?
 
anon
anon
if anything it would be due to the polynomial $x^2+x-2$
 
Jayesh Badwaik
Jayesh Badwaik
@arete No.
 
user19161
4:54 PM
@JayeshBadwaik I see. Lang's book certainly is used very often, but I prefer Petersen's book @cha. Now Petersen's book is special in that he applies the linear algebra to ordinary differential equations throughout, another very important subject on its own.
 
Jayesh Badwaik
Jayesh Badwaik
@JasperLoy Hmm. I studied that method before I studied Linear Algebra. Strange but true.
 
arete
arete
I was merely thinking that it would diverge since $\sqrt{2}$ is irrational and therefore has an infinite non repeating sequence of decimals. Thus the computer can't store the value accurately enough which will eventually lead to divergence.
 
anon
anon
@arete I suppose it is a little bit to do with the irrationality. If a fixed point can be stored fully in computer memory, then you won't have any problems, but otherwise you have to settle for approximations in which case it's possible there are instability issues.
 
arete
arete
What do you mean by "basin"?
 
anon
anon
the basin would be the region around the equilibrium point that will tends toward the point under the action of iterating the map
 
user19161
4:58 PM
@jay I have a Linux problem. I untar Firefox and transfer it from my thumbdrive to a freshly installed Debian machine. I can't run it. Yet when I download Firefox using the same machine, I can run it. Is my thumbdrive corrupted? Is there a simple explanation for this?
 
Old John
Old John
@JasperLoy could it be a permissions problem? is it a windows filesystem on the thumbdrive?
 
Jayesh Badwaik
Jayesh Badwaik
@JasperLoy There can be many simple explanations. One, which I suspect is that the file when copying loses its executable bit.
You have to make it executable again by running
$ chmod a+x <filename>
 
user19161
@OldJohn Ah, I think it is about permissions. That was the error message I think.
 
user19161
@JayeshBadwaik a+x?
 
Jayesh Badwaik
Jayesh Badwaik
assign executable bit to all the three types of entities owner, group, others
a-> all
+x -> the permission you are assigning.
 
Charlie
Charlie
5:12 PM
@JasperLoy Oh..it's beautiful...
@jay did you see what i sent ya?
 
Jayesh Badwaik
Jayesh Badwaik
@Charlie Yes.
 
Charlie
Charlie
:-D
 
Bitrex
Bitrex
5:38 PM
What's an intuitive way to explain to someone the consequences of the Green's function for the wave equation not containing a delta function in even dimensional spaces?
I'm trying to explain it to some engineering types and obviously I'm not doing a very good job because they're talking about dispersion and "welp the wave equation looks pretty much the same in all dimensions and..." sigh
 
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