docs for MINRES, only for positive definite?

[Matthew Knepley]

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 Dalcín
>  >  >> ---------------
>  >  >> Centro Internacional de Métodos Computacionales en Ingeniería (CIMEC)
>  >  >> Instituto de Desarrollo Tecnológico para la Industria Química (INTEC)
>  >  >> Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)
>  >  >> PTLC - Güemes 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 Dalcín
>  ---------------
>  Centro Internacional de Métodos Computacionales en Ingeniería (CIMEC)
>  Instituto de Desarrollo Tecnológico para la Industria Química (INTEC)
>  Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)
>  PTLC - Güemes 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