[Insight-developers] vnl_lsqr - some benchmarks

[Aljaz Noe]

We are using it. This is the default solver in current FEM code.

BTW: Solving the system of lin. eqns. is only one bottleneck. The other one
is assembling the sparse matrix.

Aljaz

> -----Original Message-----
> From: insight-developers-admin@public.kitware.com
> [mailto:insight-developers-admin@public.kitware.com]On Behalf Of Miller,
> James V (CRD)
> Sent: Wednesday, April 03, 2002 9:11 AM
> To: Insight-developers (E-mail)
> Subject: [Insight-developers] vnl_lsqr - some benchmarks
>
>
> Here is part of a discussion of using vnl_lsqr to solve
> a sparse matrix problem. Dominique says it compares
> favorably to the solvers in Matlab.
>
> Have the FEM folks tried this routine? How did this compare
> to the other solvers you have used?
>
> This user was solving systems with 3000-10000 cells (nodes?).  How
> does that compare to the meshes that you use in deformable registration?
>
>
> -----Original Message-----
> From: domi@vision.ee.ethz.ch [mailto:domi@vision.ee.ethz.ch]
> Sent: Thursday, March 28, 2002 10:47 AM
> To: Vxl-users@lists.sourceforge.net
> Subject: [Vxl-users] vnl_lsqr - some benchmarks
>
>
> Hi,
>
> You were right, Matlab gets dramatically slower with nonsymmetric
> non-only-diagonal matrix.
>
>
>   for (signed i=0; i<n; i++) {
> 	 A(i,i) = 1.0;
>
> 	 if( (i+1)<=(n-1) && (i-1)>=0 ){
> 		A(i,i+1) = 2.0;
> 		A(i,i-1) = -1.0;
> 	 }
>
> 	 b(i)           = i+1.0;
>   }
>
>
> Actually matlab gets far slower compared to
> vnl_lsqr but on the test system (above) I have:
>
> vnl_lsqr.cxx : The equations A*x = b are probably compatible.  Norm(A*x
> - b) is as small as seems reasonable on this machine.
>
> vnl solves this (n=3000) very quickly while matlab chews it much
> longer.
>
> n=10,000 is solved by vnl in 1.5 min on my machine, matlab after a
> longer while crashes screaming for memory.
>
>
> ---
>
> I have all optimisations on. I am using solaris with gcc2.95.
> No things like netscape running in bg, or two calculations running at
> the same time.
>
> ----
>
>
> I still will try svd today, just to compare.
>
>
>
> thank you for feedback
>
> dominique
>
>
>
>
>
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