On Thu, Feb 28, 2008 at 11:25 AM, Lisandro Dalcin <dalcinl at gmail.com> wrote: > Good point, the current code seems to require that...
Its not the code, its the algorithm. It requires symmetry. Matt > ierr = KSP_PCApply(ksp,R,Z);CHKERRQ(ierr); /* z <- B*r */ > ierr = VecDot(R,Z,&dp);CHKERRQ(ierr); > /*...*/ > if (dp < 0.0) { > ksp->reason = KSP_DIVERGED_INDEFINITE_PC; > PetscFunctionReturn(0); > } > > Indeed, the following (simple minded, diagonal matrix) test fails with > -pc_type jacobi, but success with -pc_type none > > import sys, petsc4py > petsc4py.init(sys.argv) > from petsc4py import PETSc > import numpy as N > A = PETSc.Mat().createAIJ([10,10]) > for i in range(0,5): > A[i,i] = -(i + 1) > for i in range(5,10): > A[i,i] = +(i + 1) > A.assemble() > A.view() > x, b= A.getVecs() > b.set(1) > ksp = PETSc.KSP().create() > ksp.type = 'minres' > ksp.setOperators(A) > ksp.setFromOptions() > ksp.solve(b,x) > > > > > On 2/28/08, Barry Smith <bsmith at mcs.anl.gov> wrote: > > > > But does it require a positive definite preconditioner? > > > > > > > > Barry > > > > > > On Feb 28, 2008, at 9:32 AM, Matthew Knepley wrote: > > > > > Docs are wrong. > > > > > > Matt > > > > > > 2008/2/28 Lisandro Dalcin <dalcinl at gmail.com>: > > >> I've noticed that the docs for MINRES say that the operator and the > > >> preconditioner must be POSITIVE DEFINITE. But I understand MINRES is > > >> tailored for the symmetric/hermitian-indefinite case. > > >> > > >> Are the docs wrong? Or the actual code is a (very peculiar) MINRES > > >> variant? > > >> > > >> > > >> -- > > >> Lisandro Dalc?n > > >> --------------- > > >> Centro Internacional de M?todos Computacionales en Ingenier?a (CIMEC) > > >> Instituto de Desarrollo Tecnol?gico para la Industria Qu?mica (INTEC) > > >> Consejo Nacional de Investigaciones Cient?ficas y T?cnicas (CONICET) > > >> PTLC - G?emes 3450, (3000) Santa Fe, Argentina > > >> Tel/Fax: +54-(0)342-451.1594 > > >> > > >> > > > > > > > > > > > > -- > > > What most experimenters take for granted before they begin their > > > experiments is infinitely more interesting than any results to which > > > their experiments lead. > > > -- Norbert Wiener > > > > > > > > > > -- > Lisandro Dalc?n > --------------- > Centro Internacional de M?todos Computacionales en Ingenier?a (CIMEC) > Instituto de Desarrollo Tecnol?gico para la Industria Qu?mica (INTEC) > Consejo Nacional de Investigaciones Cient?ficas y T?cnicas (CONICET) > PTLC - G?emes 3450, (3000) Santa Fe, Argentina > Tel/Fax: +54-(0)342-451.1594 > > -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener