PETSc version 3.17.4
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# MatSetUnfactored

Resets a factored matrix to be treated as unfactored.

### Synopsis

    #include "petscmat.h"
    PetscErrorCode MatSetUnfactored(Mat mat)

Logically Collective on Mat

### Input Parameter

| mat | - the factored matrix to be reset

### Notes

This routine should be used only with factored matrices formed by in-place factorization via ILU(0) (or by in-place LU factorization for the MATSEQDENSE format). This option can save memory, for example, when solving nonlinear systems with a matrix-free Newton-Krylov method and a matrix-based, in-place ILU(0) preconditioner.

Note that one can specify in-place ILU(0) factorization by calling

         PCType(pc,PCILU);
         PCFactorSeUseInPlace(pc);

or by using the options -pc_type ilu -pc_factor_in_place

In-place factorization ILU(0) can also be used as a local solver for the blocks within the block Jacobi or additive Schwarz methods (runtime option: -sub_pc_factor_in_place). See Users-Manual: ch_pc for details on setting local solver options.

Most users should employ the simplified KSP interface for linear solvers instead of working directly with matrix algebra routines such as this. See, e.g., KSPCreate().

### See Also

PCFactorSetUseInPlace(), PCFactorGetUseInPlace()

### Level

developer

### Location

src/mat/interface/matrix.c

### Implementations

MatSetUnfactored_MPIAIJ in src/mat/impls/aij/mpi/mpiaij.c
MatSetUnfactored_MPIBAIJ in src/mat/impls/baij/mpi/mpibaij.c
MatSetUnfactored_MPISBAIJ in src/mat/impls/sbaij/mpi/mpisbaij.c
MatSetUnfactored_MPISELL in src/mat/impls/sell/mpi/mpisell.c
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