Re: eigs arpack arpack++ and Debian

[Christophe Prud'homme]

David,

| I spent a large time about a year ago trying to get eigs running in
| octave. I have a full implementation but it is unstable. There is a
| thread about it on the maintainers list in April and May last year.
I saw a thread on this and your post. I was wondering if Debian disabled 
eigs/arpack or if it was actually implemented for good in octave.

|
| I believe there is something I'm doing incorrectly with arpack that
| makes the results unstable, and I'm not sure what. For real PD matrices,
| this means that the algorithm seems to be slower to converge than the
| matlab equivalent, whereas as for other types of matrices, the incorrect
| eigenvalues are returned. Someone who knows more about the Arnoldi
| algorithm or even better arpack itself than me really needs to look at
| this code to fix.
|
| I attach my latest version of eigs.cc to this message. To build it run
|
| % mkoctfile eigs.cc -larpack
I will have a look
I never wanted to use arpack directly but rather arpack++ which simplifies 
things a lot. Moreover you have different strategies depending on the nature 
of the problem which is easier for a human being to handle with arpack++

|
| There are integrated tests in the code that can test its full
| functionality. that can be run from the octave prompt as
|
| % test eigs.cc
|
| though you'll either need the octave CVS (or 2.9.5 that is coming out
| very shortly), or octave-forge to have the test function available.
I will get octave/cvs and see what I can do 

| If you have experience with arpack, then perhaps you might like to take
| a look at this code and see if you can see what I did wrong...
I have some experience with arpack/arpack++ which has been positive so far
As I said in my previous email I have a nice testsuite in arpack++ for a wide 
range of problems that could be helpful to debug eigs() in octave.

Best regards
C.
-- 
Christophe Prud'homme
EPFL SB IACS CMCS
MA B2 534 (Bâtiment MA)
Station 8
CH-1015 Lausanne
Tel: +41 (0)21 693 25 47
Fax: +41 (0)21 693 43 03



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