Example

The user can determine what method to take here by specifying it as follows:

  PC the_pc; /* the parallel preconditioner */
  {
    PC local_pc; /* a pointer to the local solver */
    ierr = PCParallelGetLocalPC(the_pc,&local_pc);
    /* example: set the local solve to full LU solve */
    ierr = PCSetType(local_pc,PCLU);
  }

The possible choices for the second argument are now all of the non-parallel preconditioners available in the Petsc library; see below. The default is an identity preconditioner.

The local solve type could have been set by the following option:

    -sub_pc_type lu

The subdomain solvers may need additional parameters, eg the type of sweep in the case of a PCSOR solver. This can be done using the normal functions on the local_pc:

    PCSORSetSymmetric(local_pc,SOR_SYMMETRIC_SWEEP);

See the Petsc manual for the functions and values available.

This is the list of the local methods available:

PCNONE

Do a simple copy instead of a solve; equivalently, use the identity matrix as solver.

PCJACOBI

Use the diagonal of the matrix as solver.

PCSOR

Use a triangular part of the matrix; see the Petsc manual for further options.

PCILU

Use an incomplete factorisation as solver.

PCEISENSTAT

The Eisenstat variant of ILU(0).

PCICC

Use the Cholesky incomplete factorisation; this presupposes a symmetric matrix.

with corresponding option values none, jacobi, sor, bjacobi, eisenstat, ilu, icc.