## Search found 120 matches

Fri Sep 07, 2012 3:59 am UTC
Forum: Mathematics
Topic: Density of invertible matrices
Replies: 8
Views: 2829

### Re: Density of invertible matrices

Also note that the set of invertible (n x n)-matrices in R, GL n (R), is dense in the set of (n x n)-matrices in R, R n x n (in the standard topology). To prove that you can use the fact that the determinant is a continuous function. Your statement is right, but I don't see how the determinant bein...
Fri Aug 03, 2012 4:51 am UTC
Topic: 1090: "Formal Languages"
Replies: 90
Views: 30620

### Re: 1090: "Formal Languages"

HonoreDB wrote:Scaling Everest was, by far, the most amazing and transformative experience of my life.

Based on the context I'm really afraid I'm missing a subtle pun.
Thu Jun 07, 2012 6:18 am UTC
Forum: Mathematics
Topic: Comprehension of proof - tangent vectorspace on manifold
Replies: 1
Views: 1444

### Re: Comprehension of proof - tangent vectorspace on manifold

It seems to me like you're "plugging in too soon". An analogous mistake is this: "Let f(x) = x^2". The derivative of f at 0 is zero. Here's why: f(0) = 0. The derivative of 0 is zero." You say since we are taking about TpM, x=0, but there is no "global variable" x ...
Thu Jun 17, 2010 11:03 pm UTC
Forum: Mathematics
Topic: Fun math questions for (relative) beginners
Replies: 9
Views: 1904

### Re: Fun math questions for (relative) beginners

Visualization helped a lot when I was explaining completing the square to someone recently: http://upload.wikimedia.org/wikipedia/commons/a/a3/Completing_the_square_307.PNG From Wikipedia's article. Not really a problem, but probably useful. One puzzle I like is: We have 32 rectangular tiles whi...
Thu May 27, 2010 6:39 pm UTC
Forum: Coding
Topic: Manufactoria - Make Turing Machines with Conveyor Belts
Replies: 350
Views: 126889

### Re: Manufactoria - Make Turing Machines with Conveyor Belts

You might want to write some better test cases for the comparison one. I just wrote something which chops off leading zeros and compares lengths, and tested that, and it passed everything.

Edit: I just tried the kongregate version, and I got a 404 (just in the game box).
Thu Apr 22, 2010 2:45 am UTC
Forum: The Help Desk
Topic: I'm really starting to hate javascript
Replies: 16
Views: 1860

### Re: I'm really starting to hate javascript

Well, not really, since PHP is all executed on the server, and firebug is part of your client.

But firebug can also look at requests and replies that are sent to and from your server, which can be helpful when doing certain things with php.
Wed Mar 24, 2010 11:25 pm UTC
Forum: Mathematics
Topic: Famous Math Quotes!
Replies: 32
Views: 8160

### Re: Famous Math Quotes!

"The above proposition [2+2=4] is occasionally useful."
-Principia Mathematica
Tue Mar 09, 2010 2:45 am UTC
Forum: The Help Desk
Topic: openGL newb: creating images
Replies: 2
Views: 502

### Re: openGL newb: creating images

Using qpainter makes much more sense, actually. I was looking for something like that to use instead of OpenGL. Thanks.
Mon Mar 08, 2010 11:40 pm UTC
Forum: The Help Desk
Topic: openGL newb: creating images
Replies: 2
Views: 502

### openGL newb: creating images

I'm working on creating a 2d Sierpinski triangle type image in opengl, which I would like to have on a file so I can print it out. I've run into a couple of problems. 1. I'm trying to export it to a tiff. I'm using libtiff and the writetiff.c example that is found here: http://www.opengl.org/resourc...
Wed Mar 03, 2010 6:46 am UTC
Forum: Mathematics
Topic: Cartesian Product
Replies: 5
Views: 855

### Re: Cartesian Product

What's (i,0)^4, with (i,0) in C^2?

What's (0,1,0,0)^4, with (0,1,0,0) in R^2?
Tue Dec 22, 2009 8:44 pm UTC
Forum: Mathematics
Topic: Do E-Harmony's 29 Dimensions form an Orthogonal Basis?
Replies: 17
Views: 2751

### Re: Do E-Harmony's 29 Dimensions form an Orthogonal Basis?

Perhaps, "orthonormal basis", would have been a better choice of words in the subject line. Thanks for pointing that out. It made me look up the difference between orthogonal and orthonormal. They would only need to be linearly independent. For example, the vectors (1,1) and (0,1) are lin...
Wed Nov 11, 2009 7:14 am UTC
Forum: Food
Topic: How to clean dishes?
Replies: 12
Views: 2229

### Re: How to clean dishes?

Sun Nov 08, 2009 2:07 am UTC
Forum: Mathematics
Topic: Bijection from R to R without 0 (nevermind)
Replies: 1
Views: 1144

### Bijection from R to R without 0 (nevermind)

What's a bijection from R, the reals, to R-{0}? I'm going crazy not being able to think of one, but I know there must be one.

Thanks.

Edit:
0->1/2
n-1/n -> n/n+1 for all integers n
Anything which is not 0 or (n-1)/n for some n then it maps to itself.

That should work.
Sat Oct 17, 2009 10:49 pm UTC
Forum: Mathematics
Topic: y = x sin x
Replies: 6
Views: 4983

### Re: y = x sin x

If you have y=x sin(x) and y=x, and you want to know where you meet, set the y's equal to each other: x = x sin(x). When does x = x sin(x)?
Fri Oct 16, 2009 3:22 am UTC
Forum: Coding
Topic: Grokking libnotify
Replies: 6
Views: 1123

### Re: Grokking libnotify

I have some idea of what you said, but I don't know the answer, but CortoPasta's post made me laugh.
Fri Oct 09, 2009 1:30 am UTC
Forum: Mathematics
Topic: Calculus Noob Seeking Help
Replies: 8
Views: 1328

### Re: Calculus Noob Seeking Help

What is [imath]\sin ^3 x + \sin ^3 | x |[/imath] equal to when x>0? What's the difference when x<0?

What does it mean for it to be continuous? What does it mean for it to have a derivative?
Mon Oct 05, 2009 7:47 am UTC
Topic: 0645: "RPS"
Replies: 185
Views: 51845

### Re: "RPS" Discussion

Theogrin wrote:Eat well, my friends, then go Forth and spread the word.

I thought the comic was very good, and I also appreciated that.
Sat Sep 26, 2009 4:00 pm UTC
Forum: Mathematics
Topic: What's the coolest thing you've ever learned in math class?
Replies: 58
Views: 6806

### Re: What's the coolest thing you've ever learned in math class?

I'm trying to understand the prisoner-hat proof. When it says "two sequences are identical if they are the same after a finite number of entries" what exactly does that mean? Is it "For all finite n, sequence one from digit 1 to n is the same as sequence two from digit 1 to n"? O...
Tue Sep 15, 2009 4:44 am UTC
Forum: Mathematics
Topic: A number line/plane/space thing.
Replies: 22
Views: 2426

### Re: A number line/plane/space thing.

Is addition associative in this line/plane/space thing?

If so, -x = -x+0 = -x + (x + z+u) = (-x+x) + z + u = 0 + z + u = z + u
-x=z+u

Of course, it could be that adding colors in different orders doesn't produce the same result.
Sun Sep 13, 2009 7:16 pm UTC
Forum: Coding
Topic: How is web programming... done...?
Replies: 15
Views: 2587

### Re: How is web programming... done...?

If you're looking for a simple way to set up a server on your computer to start out with, try xampp. It bundles apache and php and sql in an easy way.
Sat May 23, 2009 2:10 am UTC
Forum: Coding
Topic: Problem with Euler problem #3 in python
Replies: 40
Views: 3368

### Re: Problem with Euler problem #3 in python

Note that you don't even have to test only prime numbers by that algorithm, you can test non-prime (composite) numbers as well. The number you're testing against will just never be divisible by them. For example, 140 is divisible by 4. However, the algorithm goes: Check 2, divide by 2, we have 70. C...
Wed Apr 22, 2009 3:36 am UTC
Forum: Coding
Topic: The Ackemann evaluator 2: Overcoming recursion
Replies: 4
Views: 664

### Re: The Ackemann evaluator 2: Overcoming recursion

I believe OP has his arguments flipped.
Mon Apr 20, 2009 8:29 pm UTC
Forum: Coding
Topic: Programs without console pop ups
Replies: 15
Views: 1214

### Re: Programs without console pop ups

In case that wasn't clear: you should have a program called pythonw.exe in your python folder. Use that instead of python.exe.
Thu Mar 12, 2009 8:33 pm UTC
Forum: The Help Desk
Topic: Alternating python and cmd.exe... odd behavior
Replies: 2
Views: 657

### Alternating python and cmd.exe... odd behavior

So I have a shortcut to python.exe in C:/BATCH, and C:/BATCH is in my path variable. Since it's a shortcut, it's actually python.exe.lnk I got some very weird behavior: C:\>python.exe.lnk C:\>Python 2.5.2 (r252:60911, Feb 21 2008, 13:11:45) [MSC v.1310 32 bit (Intel)] on win32 Type "help",...
Mon Mar 02, 2009 11:55 pm UTC
Forum: Coding
Replies: 8
Views: 545

### Re: Java && Mouse Adapters

I've never seen this syntax:

Code: Select all

private Class varName = new Class(){  function declaration};

I tried implementing something like that, but I just had a compiler error saying it couldn't find Class.function() when I called varName.function().
Can someone explain or send me to a site of explanation?
Sat Feb 21, 2009 1:14 am UTC
Forum: Coding
Topic: Common Lisp macro to setq multiple symbols
Replies: 2
Views: 428

### Re: Common Lisp macro to setq multiple symbols

Ah, thanks. I guess I was thinking about the macro like a function too much, and not as a list generator.
Fri Feb 20, 2009 10:56 pm UTC
Forum: Coding
Topic: Common Lisp macro to setq multiple symbols
Replies: 2
Views: 428

### Common Lisp macro to setq multiple symbols

I have: (defclass atm () ()) I want to be able to say: (atms a b c) and have a, b, and c be set to a new instance of atom. I'm able to do what I want for just one symbol: [2] CL-USER(205): (defmacro atm (sym) `(setq ,sym (make-instance 'atm))) ATM [2] CL-USER(206): (atm d) #<ATM @ #x206fe1f2> [2] CL...
Thu Nov 20, 2008 1:59 am UTC
Forum: Mathematics
Topic: If sleep were multiplicative. . .
Replies: 9
Views: 1460

### Re: If sleep were multiplicative. . .

Yesterday I slept for two .5 hour blocks, and got .25 hours of sleep.
Today I slept for 30 minutes in the morning, and 30 minutes in the afternoon, and got 900 minutes of sleep.

The problem is that units change under multiplication.
Thu Aug 07, 2008 4:37 am UTC
Forum: Science
Topic: glow in the dark crab claw no joke guys what is this
Replies: 9
Views: 1785

### glow in the dark crab claw no joke guys what is this

Hello. I just found a glow-in-the-dark claw, that looks like it belongs to a crab. I found it on the beach. I'm sure it's not a toy, because it feels like crab claw material, and has a fishy smell. I found the claw attached to part of the leg. The part that seems to glow the most is the joint betwee...
Tue Jul 22, 2008 2:10 pm UTC
Forum: Mathematics
Topic: Odd Multiplication Trick on your Hands
Replies: 10
Views: 3321

### Re: Odd Multiplication Trick on your Hands

v1ND wrote:Does anyone know a good trick for multiplying by 10?

Just figure out 9*x, then add x.
Thu Jul 10, 2008 12:51 am UTC
Forum: The Help Desk
Topic: Windows and missing HD space
Replies: 10
Views: 2064

### Re: Windows and missing HD space

Ah, thanks. You can actually do it straight from Windows Explorer: Tools->Options->View Tab->Uncheck "Hide protected oeprating system files" and select "show hidden files and folders". The hibernate file was 2GB, and the page file was 2GB. I should have remembered those. Thanks f...
Thu Jul 10, 2008 12:34 am UTC
Forum: The Help Desk
Topic: Windows and missing HD space
Replies: 10
Views: 2064

### Windows and missing HD space

Hello. I got a new Lenovo laptop with XP. I got a 75 GB hard drive. I planned to have a 20 GB Windows partition, and the rest a Linux partition. Well, 6.7 GB of my HD goes to this partition called SERVICEV001, which puts my initial partition at 67.8 GB It holds back up files, I guess. Would there be...
Mon May 19, 2008 10:11 pm UTC
Forum: Mathematics
Topic: so maths is useful for what now?
Replies: 31
Views: 3711

### Re: so maths is useful for what now?

The shape of the pendant that I desire is given by the rotation of |sin(x2)+2| from x=0 to x=4cm around the x axis. I want a 2 carat embedded diamond. What is the volume of the gold needed to make my pendant? What is the surface area of the pendant?
Tue Apr 15, 2008 11:06 pm UTC
Forum: Hardware
Topic: ******NEWS FLASH: This is it for Microsoft******
Replies: 17
Views: 3210

### Re: ******NEWS FLASH: This is it for Microsoft******

Oh me yarm is this serious??? i just bought vista and i need support for it. they better still support it becasue I don't want to pay like 1000 dollars for macintosh just to be able to get support fgor it.

its just a corporate thing rite?? Or is the products effected?
Tue Mar 25, 2008 9:15 pm UTC
Forum: Mathematics
Topic: initial question
Replies: 3
Views: 933

### Re: initial question

Wow, I've never noticed that, but looking back in topics it is always true.
Mon Mar 24, 2008 3:50 pm UTC
Forum: Mathematics
Replies: 393
Views: 62011

### Re: Amusing answers to tests

Write something that has nothing to do with the topic.
Wed Mar 12, 2008 11:32 pm UTC
Forum: Mathematics
Topic: Math bloopers heard in math classes
Replies: 252
Views: 36022

### Re: Math bloopers heard in math classes

Commence necromancy. I was at an academic team meet. There was a question, not addressed to me, that went like this: "You throw 3 dice simultaneously. What's the chance that all three of them will be the same number?" They had no idea. I can excuse that. Most people at these things freeze ...
Wed Mar 12, 2008 11:05 am UTC
Forum: Language/Linguistics
Topic: I would hate to be able to read Chinese characters...
Replies: 10
Views: 3795

### Re: I would hate to be able to read Chinese characters...

Sun Mar 09, 2008 7:04 pm UTC
Forum: Mathematics
Topic: Why do people dislike maths so much?
Replies: 258
Views: 29631

### Re: Why do people dislike maths so much?

This is where people make the horrible horrible mistake of viewing maths as uncreative, or fixed and rigid[ I wrote a college essay on that. I was doodling while procrastinating about the essay, and I drew a clam. Then I found a polar function whose graph resembles a clam, and wrote about the funct...
Tue Feb 26, 2008 11:04 pm UTC
Forum: Coding
Topic: Starting Java : AP CS Gridworld problems
Replies: 4
Views: 2184

### Starting Java : AP CS Gridworld problems

Hello. I am taking the AP CS test, without having taken the class. I've done a bit of Java, but nothing too serious. I'm having a bit of trouble with setting up the grid world thing. The grid world code can be found here. I'm running Ubuntu 7.10, and I have Eclipse. My Java version: tim@TimRoom:~\$ j...