PCSetOperators

Sets the matrix associated with the linear system and a (possibly) different one associated with the preconditioner.

Synopsis

int PCSetOperators(PC pc,Mat Amat,Mat Pmat,MatStructure flag)
Collective on PC and Mat

Input Parameters

pc - the preconditioner context
Amat - the matrix associated with the linear system
Pmat - matrix to be used in constructing preconditioner, usually the same as Amat.
flag - flag indicating information about the preconditioner matrix structure during successive linear solves. This flag is ignored the first time a linear system is solved, and thus is irrelevant when solving just one linear system.

Notes

The flag can be used to eliminate unnecessary work in the preconditionerduring the repeated solution of linear systems of the same size. Theavailable options are
SAME_PRECONDITIONER - Pmat is identical during successive linear solves. This option is intended for folks who are using different Amat and Pmat matrices and wish 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.

Caution

If you specify SAME_NONZERO_PATTERN, PETSc believes your assertionand does not check the structure of the matrix. If you erroneouslyclaim that the structure is the same when it actually is not, the newpreconditioner will not function correctly. Thus, use this optimizationfeature carefully!

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

More Notes about Repeated Solution of Linear Systems

PETSc does NOT reset the matrix entries of either Amat or Pmatto zero after a linear solve; the user is completely responsible formatrix assembly. See the routine MatZeroEntries() if desiring tozero all elements of a matrix. .keywords: PC, set, operators, matrix, linear system

See Also

PCGetOperators(), MatZeroEntries()

Location: src/pc/interface/precon.c
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