[Insight-developers] vnl_lsqr - some benchmarks

[Miller, James V (CRD)]

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





_______________________________________________
Vxl-users mailing list
Vxl-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/vxl-users