[Getdp] Q: Lanczos error

[Christophe Geuzaine]

スズキ wrote:

> Hi,
> 
> I'm new to getdp (on Windows).  I tried to solve a 
> simple eigenvalue problem using lanczos, and got an 
> error: "Lanczos algorithm not available with the GSL".  
> Questions:
> 
> (1) I took a look at the source code and found that 
> lanczos routines are intentionally disabled when 
> HAVE_GSL is defined.  Why is that?

Hi - It's because Lanczos currently uses non-free routines from the
Numerical Recipes (for the QR decomposition, IIRC), and has not been
translated yet to use the GSL (the GNU Scientific Library:
http://sources.redhat.com/gsl/).

> 
> (2) Is there a way to solve eigenvalue problems, 
> either by enabling lanczos, or by using another 
> algorithm?  

Lanczos is the only algorithm implemented in the code at the moment.
Adding another algorithm (or modifying Lanczos to use the GSL) should be
pretty simple... Your code contribution is very much welcome :-)

> 
> (3) I found a simple wave equation example in the 
> mailing-list archive, in which the formulation is 
> in time domain and resolution contains lanczos.  Does 
> it mean that specifying lanczos automatically convert 
> time-FEM into frequency domain, so I don't have to 
> rewrite FEM manually for lanczos?  

Yes, exactly.

Cheers,

Christophe

-- 
Christophe Geuzaine
Applied and Computational Mathematics, Caltech
geuzaine at acm.caltech.edu - http://geuz.org