Ask HN: what linear algebra do you use most often for practical problems? • Hacker News Board

Re: Ask HN: what linear algebra do you use most often for practical problems?

#21

Post by physcab » Fri, Apr 10, 2009, 4:33 PM UTC

buss wrote: post #19

jey wrote: post #14

Earlier quoted context omitted.

I've been using PROPACK lately to perform SVD on a gigantic matrix, and it kicks ass. It's a fortran and/or MATLAB package for SVD of large sparse or "structured" matrices. http://soi.stanford.edu/~rmunk/PROPACK/ You just have to provide a matrix-vector product function, specify a few parameters (how many singular values to find, should it compute the singular vectors, maximum number of iterations, etc) and it takes…

I'd be interested in trying it out, can you send it my way a la sbuss a cise d ufl d edu Cheers

Hey, I'm at UFL too! I'm taking Dr. Gader's class in machine learning right now. Are you a grad student?

Re: Ask HN: what linear algebra do you use most often for practical problems?

#22

Post by vang3lis » Fri, Apr 10, 2009, 5:44 PM UTC

jey wrote: post #16

I'm using SVD in building a porn recommendation engine. (Very NSFW, and the recommendation engine itself isn't live yet: http://fapseek.com )

maybe you could opensource your dataset? ;) (no, no, I'm after votes not images)

Re: Ask HN: what linear algebra do you use most often for practical problems?

#23

Post by krakensden » Fri, Apr 10, 2009, 6:15 PM UTC

jey wrote: post #16

I'm using SVD in building a porn recommendation engine. (Very NSFW, and the recommendation engine itself isn't live yet: http://fapseek.com )

Now there is a quality name for a porn recommendation engine...

Re: Ask HN: what linear algebra do you use most often for practical problems?

#24

Post by darkxanthos » Fri, Apr 10, 2009, 6:33 PM UTC

jey wrote: post #17

omarish wrote: post #7

You can save a ton of time by formulating a linear algebra problem as a shortest path problem; you can end up using dijkstra's algorithm to enumerate the possible solutions. http://en.wikipedia.org/wiki/Knapsack_problem

I don't get it (at all). Can you elaborate?

He's saying basically, instead of manipulating a bunch of data algebraically to get the exactly provably right answer you can use this other algo to get you a damn good answer faster. (I think)

Re: Ask HN: what linear algebra do you use most often for practical problems?

#25

Post by keefe » Fri, Apr 10, 2009, 7:18 PM UTC

It's not a very interesting answer, but technically linear algebra : transformation matrices for rotating and scaling graphics...

Re: Ask HN: what linear algebra do you use most often for practical problems?

#26

Post by jey » Fri, Apr 10, 2009, 7:22 PM UTC

vang3lis wrote: post #22

jey wrote: post #16

I'm using SVD in building a porn recommendation engine. (Very NSFW, and the recommendation engine itself isn't live yet: http://fapseek.com )

maybe you could opensource your dataset? ;) (no, no, I'm after votes not images)

Not anytime soon, but I might eventually provide a representative subset and run something like the Netflix Prize.

Re: Ask HN: what linear algebra do you use most often for practical problems?

#27

Post by frankus » Fri, Apr 10, 2009, 7:32 PM UTC

I've poked around the CGAffineTransform classes that Apple uses in their Core Animation framework a bit, but unless you're doing something out of the ordinary, you don't really need to know what's going on under the hood.

Re: Ask HN: what linear algebra do you use most often for practical problems?

#28

Post by njoubert » Fri, Apr 10, 2009, 7:45 PM UTC

Generating Jacobians for Implicit Euler Integration in a numerical simulation project. SVD for rigid body center-of-mass calculations. Conjugate Gradient for solving Ax=b on 9000x9000 matrices.

Re: Ask HN: what linear algebra do you use most often for practical problems?

#29

Post by kobs » Fri, Apr 10, 2009, 8:38 PM UTC

physcab wrote: post #21

buss wrote: post #19

Earlier quoted context omitted.

I'd be interested in trying it out, can you send it my way a la sbuss a cise d ufl d edu Cheers

Hey, I'm at UFL too! I'm taking Dr. Gader's class in machine learning right now. Are you a grad student?

I think there are a couple of gators on HN.

Re: Ask HN: what linear algebra do you use most often for practical problems?

#30

Post by jey » Sun, Apr 12, 2009, 10:28 AM UTC

redrobot5050 wrote: post #20

jey wrote: post #16

I'm using SVD in building a porn recommendation engine. (Very NSFW, and the recommendation engine itself isn't live yet: http://fapseek.com )

You hiring?

Email me.