petsc-3.5.4 2015-05-23

MatGetOrdering

Gets a reordering for a matrix to reduce fill or to improve numerical stability of LU factorization.

Synopsis

#include "petscmat.h" 
PetscErrorCode  MatGetOrdering(Mat mat,MatOrderingType type,IS *rperm,IS *cperm)

Collective on Mat

Input Parameters

	mat	- the matrix
	type	- type of reordering, one of the following:

     MATORDERINGNATURAL - Natural

     MATORDERINGND - Nested Dissection

     MATORDERING1WD - One-way Dissection

     MATORDERINGRCM - Reverse Cuthill-McKee

     MATORDERINGQMD - Quotient Minimum Degree

Output Parameters

	rperm	- row permutation indices
	cperm	- column permutation indices

Options Database Key

-mat_view_ordering draw -plots matrix nonzero structure in new ordering

Notes

This DOES NOT actually reorder the matrix; it merely returns two index sets that define a reordering. This is usually not used directly, rather use the options PCFactorSetMatOrderingType()

The user can define additional orderings; see MatOrderingRegister().

These are generally only implemented for sequential sparse matrices.

The external packages that PETSc can use for direct factorization such as SuperLU do not accept orderings provided by this call.

Keywords

matrix, set, ordering, factorization, direct, ILU, LU,
fill, reordering, natural, Nested Dissection, One-way Dissection, Cholesky, Reverse Cuthill-McKee, Quotient Minimum Degree

Examples

src/mat/examples/tutorials/ex1.c.html
src/ksp/ksp/examples/tutorials/ex18.c.html