[Gsll-devel] Problems with SVD through gsll on OS X 10.5 with SBCL

[Nimalan Mahendran]

Hi,

Sorry, I made a stupid/obvious mistake - (unsigned-byte 32) instead of
some kind of floating-point number :P It would be nice to have an
error message though..

Thanks for gsll, it's been pretty useful so far.

On Fri, Jun 19, 2009 at 12:54 AM, Nimalan
Mahendran<nimalan.mahendran at gmail.com> wrote:
> Hello everyone,
>
> I'm trying to see whether I could use SBCL (or whatever CL
> implementation) as an alternative for Matlab in machine learning
> research. I have gsll running, but I saw that gsll's SVD,
> (sv-decomposition u s v) is converging to the wrong answers for the
> identity matrix.
>
>>> M = [1 0 0; 0 1 0; 0 0 1]
>
> but Matlab's SVD works fine.
>
> Here's what happens in gsll/SBCL:
>
> (setf M1
>      (MAKE-MARRAY '(UNSIGNED-BYTE 32) :INITIAL-CONTENTS
>                   '((1 0 0) (0 1 0) (0 0 1))))
> (setf u (copy m1))
> (setf s (make-marray 'vector-unsigned-byte-32 :dimensions 3))
> (setf v (make-marray 'matrix-unsigned-byte-32 :dimensions '(3 3)))
> (sv-decomposition u s v)
>
> GSL> u
> #<MATRIX-UNSIGNED-BYTE-32 #2A((0 0 0)
>                              (2147483648 0 3220176896)
>                              (0 2147483648 0))>
> GSL> s
> #<VECTOR-UNSIGNED-BYTE-32 #(268809831 296241371 268543215)>
> GSL> v
> #<MATRIX-UNSIGNED-BYTE-32 #2A((2083159301 2991920483 0)
>                              (2147483648 0 1072693248)
>                              (0 3220176896 0))>
> GSL>
>
> The answers are definitely not right.. I don't think the right memory
> addresses are even being accessed.
>
> I noticed in the definition of SV-decomposition in svd.lisp, the
> :outputs parameter is (A S V), but according to the GSL documentation
> at http://www.gnu.org/software/gsl/manual/html_node/Singular-Value-Decomposition.html,
> maybe it should be (A V S)? I'm not sure how these parameters to
> defmfun actually work or what they mean (although I am familiar with
> cffi..). I was getting the same numbers even when I did SVD on this
> matrix:
>
>>> M = [1 0 0; 0 2 0; 0 0 3]
>
> so a memory access error seems likely to me.
>
> Would someone mind helping me fix this?
>
> Thanks!
> --
> Nimalan Mahendran
>



-- 
Nimalan Mahendran