Changes matrix ordering to remove zeros from diagonal. This may help in the LU factorization to prevent a zero pivot.
PetscErrorCode MatReorderForNonzeroDiagonal(Mat mat,PetscReal abstol,IS ris,IS cis)
Collective on Mat
|mat ||- matrix to reorder
|rmap,cmap ||- row and column permutations. Usually obtained from
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 SeqAIJ matrices
Options Database Keys (When using KSP)
Column pivoting is used.
1) 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).
2) 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
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