Math Forum Discussions

Loesche

Posts: 16
Registered: 12/7/04

Again: Matlab for Linux and svd
Posted: Nov 7, 1996 1:05 PM

Plain Text

C_22.mat (0.3 K)

Hi folks,

a couple of days ago I posted a message and just one person
responded.
Maybe I didn't point at the problem straight forward enough.

Here it comes again:

I have a matrix "C_22" which is real and 6x6. (I included it at
the end.) It is supposed to have all singular values close to
1.
When I load this matrix into Matlab and try to compute the
singular values or the spectral norm, I get errors like

>> svd(C_22)
??? Error using ==> svd
Solution will not converge.

or

>> norm(C_22)
??? Error using ==> norm
Solution will not converge.

Unfortunately, this error terminates the computation and I have
some jobs running for hours.
I assume that svd or norm are heavily used inside Matlab and I do not
know when this error will occur.

It seems to be caused libc.so or libm.so.
I reported this problem to TMW and their workaround was to add
some noise to the matrix. Unfortunately this does not work for me.

I am running the update of Matlab for Linux which can be found
on ftp.mathworks.com. The binary on the CD-ROM shipped by TMW
segfaults under my Linux kernel.
I use Linux kernel 2.0.0 (2.0.20 does not solve the problem) from
the (german) "S.U.S.E.ÃÂ Linux 4.2" distribution.
The error occurrs regardless of the processor Matlab is running on.
(I verified 486DX/2-66, P5-133 (new one - not with the fdiv bug),
P5-150 (new as well), and a P6-200.)

Here are my questions:

1) Is there anybody out there running Linux 2.0.0 (or newer) AND
the update from TMW who can compute the singular values of C_22?
If so, please tell me what distribution of Linux and
combination of kernel and libraries (libm.so, libc.so...)
are used.

2) Is there anybody with Linux 2.0.* running the ORIGINAL binary
from the installation CD-ROM?
Under Linux 1.2.13 this was running smoothly and svd/norm
worked...

3) This one is for TMW specially! Is it possible (and if, how) to
replace a built-in function like svd or norm by a MEX-file?
The svd-solver from LAPACK-2.0 converges and I would like to
replace the built-in solver by the LAPACK solver.
(A straight forward approach didn't work.)

Here the uuencoded matrix comes:

At the moment downgrading to an out-of-date 1.2.13 distribution and
using the original binary seems to be the only way to get a working
Matlab.

Thank you for your efforts!

Cheers, Ralf

ps: Even on C_22(4:6,4:6) svd or norm does not work!
On our Sparc20 I get the right answers.