KSPSetOperators

Synopsis

#include "petscksp.h" 
PetscErrorCode  KSPSetOperators(KSP ksp,Mat Amat,Mat Pmat,MatStructure flag)

Input Parameters

Notes

   SAME_PRECONDITIONER -

     Pmat is identical during successive linear solves.

     This option is intended for folks who are using

     different Amat and Pmat matrices and want to reuse the

     same preconditioner matrix.  For example, this option

     saves work by not recomputing incomplete factorization

     for ILU/ICC preconditioners.

   SAME_NONZERO_PATTERN -

     Pmat has the same nonzero structure during

     successive linear solves. 

   DIFFERENT_NONZERO_PATTERN -

     Pmat does not have the same nonzero structure.

All future calls to KSPSetOperators() must use the same size matrices!

Passing a PETSC_NULL for Amat or Pmat removes the matrix that is currently used.

If you wish to replace either Amat or Pmat but leave the other one untouched then first call KSPGetOperators() to get the one you wish to keep, call PetscObjectReference() on it and then pass it back in in your call to KSPSetOperators().

Caution

If in doubt about whether your preconditioner matrix has changed structure or not, use the flag DIFFERENT_NONZERO_PATTERN.

Alternative usage: If the operators have NOT been set with KSP/PCSetOperators() then the operators are created in PC and returned to the user. In this case, if both operators mat and pmat are requested, two DIFFERENT operators will be returned. If only one is requested both operators in the PC will be the same (i.e. as if one had called KSP/PCSetOperators() with the same argument for both Mats). The user must set the sizes of the returned matrices and their type etc just as if the user created them with MatCreate(). For example,

        KSP/PCGetOperators(ksp/pc,&mat,PETSC_NULL,PETSC_NULL); is equivalent to

          set size, type, etc of mat

        MatCreate(comm,&mat);

        KSP/PCSetOperators(ksp/pc,mat,mat,SAME_NONZERO_PATTERN);

        PetscObjectDereference((PetscObject)mat);

          set size, type, etc of mat

and

        KSP/PCGetOperators(ksp/pc,&mat,&pmat,PETSC_NULL); is equivalent to

          set size, type, etc of mat and pmat

        MatCreate(comm,&mat);

        MatCreate(comm,&pmat);

        KSP/PCSetOperators(ksp/pc,mat,pmat,SAME_NONZERO_PATTERN);

        PetscObjectDereference((PetscObject)mat);

        PetscObjectDereference((PetscObject)pmat);

          set size, type, etc of mat and pmat

The rational for this support is so that when creating a TS, SNES, or KSP the hierarchy of underlying objects (i.e. SNES, KSP, PC, Mat) and their livespans can be completely managed by the top most level object (i.e. the TS, SNES, or KSP). Another way to look at this is when you create a SNES you do not NEED to create a KSP and attach it to the SNES object (the SNES object manages it for you). Similarly when you create a KSP you do not need to attach a PC to it (the KSP object manages the PC object for you). Thus, why should YOU have to create the Mat and attach it to the SNES/KSP/PC, when it can be created for you?

Keywords

See Also

Level:beginner
Location:src/ksp/ksp/interface/itcreate.c
Index of all KSP routines
Table of Contents for all manual pages
Index of all manual pages

Examples