MatReorderForNonzeroDiagonal#
Changes matrix ordering to remove zeros from diagonal. This may help in the PCLU
factorization to prevent a zero pivot.
Synopsis#
#include "petscmat.h"
PetscErrorCode MatReorderForNonzeroDiagonal(Mat mat, PetscReal abstol, IS ris, IS cis)
Collective
Input Parameters#
mat - matrix to reorder
rmap,cmap - row and column permutations. Usually obtained from
MatGetOrdering()
.
Notes#
This is not intended as a replacement for pivoting for matrices that
have ``bad’’ structure. It is only a stop-gap measure. Should be called
after a call to MatGetOrdering()
, this routine changes the column
ordering defined in cis.
Only works for MATSEQAIJ
matrices
Options Database Keys (When using KSP
)#
-pc_factor_nonzeros_along_diagonal - Reorder to remove zeros from diagonal
Algorithm Notes#
Column pivoting is used.
Choice of column is made by looking at the non-zero elements in the troublesome row for columns that are not yet included (moving from left to right).
If (1) fails we check all the columns to the left of the current row and see if one of them has could be swapped. It can be swapped if its corresponding row has a non-zero in the column it is being swapped with; to make sure the previous nonzero diagonal remains nonzero
Level#
intermediate
Location#
Index of all Mat routines
Table of Contents for all manual pages
Index of all manual pages