On Oct 22, 2014, at 1:25 AM, Jed Brown <[email protected]> wrote:

Barry Smith <[email protected]> writes:

...

Jed

There are some additional issues when the GMRES runs for zero iterations in computing eigenvalues for Cheby.

Hmm, what is right?

I don’t know. I was never a big fan of Chebyshev smoothing anyways :-) I do know that the current situation is bad Barry

Suggest that the user set -ksp_chebyshev_estimate_eigenvalues_random? Automatically fall back to that?

Just picking arbitrary values doesn't seem right because the solver won't work right on the next solve.

...

static PetscErrorCode KSPChebyshevComputeExtremeEigenvalues_Private(KSP kspest,PetscReal *emin,PetscReal *emax) { PetscErrorCode ierr; PetscInt n,neig; PetscReal *re,*im,min,max;

PetscFunctionBegin; ierr = KSPGetIterationNumber(kspest,&n);CHKERRQ(ierr); ierr = PetscMalloc2(n,&re,n,&im);CHKERRQ(ierr); ierr = KSPComputeEigenvalues(kspest,n,re,im,&neig);CHKERRQ(ierr); min = PETSC_MAX_REAL; max = PETSC_MIN_REAL; for (n=0; n<neig; n++) { min = PetscMin(min,re[n]); max = PetscMax(max,re[n]); } ierr = PetscFree2(re,im);CHKERRQ(ierr); *emax = max; *emin = min;

* thread #1: tid = 0x3c16cf, 0x00000001041b6777 libpetsc.3.5.dylib`KSPSolve_Chebyshev(ksp=0x00007fb85197ac60) + 1495 at cheby.c:378, queue = 'com.apple.main-thread', stop reason = step over frame #0: 0x00000001041b6777 libpetsc.3.5.dylib`KSPSolve_Chebyshev(ksp=0x00007fb85197ac60) + 1495 at cheby.c:378 375 cheb->emin = cheb->tform[0]*min + cheb->tform[1]*max; 376 cheb->emax = cheb->tform[2]*min + cheb->tform[3]*max; 377 -> 378 cheb->estimate_current = PETSC_TRUE; 379 } 380 381 ksp->its = 0; (lldb) p cheb->emin (PetscReal) $11 = -1.7976931348623158E+307 (lldb) p cheb->emax (PetscReal) $12 = -Inf

This puts giberish into the eigenvalue estimates.

I am not sure how you want to handle this?

The zero right hand side zero, initial guess case is a great corner case for testing complicated solvers :-) I’d forgotten about it for many years