# MatSetOption

Sets a parameter option for a matrix. Some options may be specific to certain storage formats. Some options determine how values will be inserted (or added). Sorted, row-oriented input will generally assemble the fastest. The default is row-oriented, nonsorted input.

### Synopsis

    #include "petscmat.h"
    PetscErrorCode  MatSetOption(Mat mat,MatOption op)

Collective on Mat

### Input Parameters

| mat | - the matrix
| option | - the option, one of those listed below (and possibly others), e.g., MAT_ROWS_SORTED, MAT_NEW_NONZERO_LOCATION_ERR

### Options Describing Matrix Structure

| MAT_SYMMETRIC | - symmetric in terms of both structure and value
| MAT_HERMITIAN | - transpose is the complex conjugation
| MAT_STRUCTURALLY_SYMMETRIC | - symmetric nonzero structure
| MAT_NOT_SYMMETRIC | - not symmetric in value
| MAT_NOT_HERMITIAN | - transpose is not the complex conjugation
| MAT_NOT_STRUCTURALLY_SYMMETRIC | - not symmetric nonzero structure
| MAT_SYMMETRY_ETERNAL | - if you would like the symmetry/Hermitian flag you set to be kept with all future use of the matrix including after MatAssemblyBegin/End() which could potentially change the symmetry structure, i.e. you KNOW the matrix will ALWAYS have the property you set.
| MAT_NOT_SYMMETRY_ETERNAL | - if MatAssemblyBegin/End() is called then the flags you set will be dropped (in case potentially the symmetry etc was lost).

### Options For Use with MatSetValues()

Insert a logically dense subblock, which can be

| MAT_ROW_ORIENTED | - row-oriented (default)
| MAT_COLUMN_ORIENTED | - column-oriented
| MAT_ROWS_SORTED | - sorted by row
| MAT_ROWS_UNSORTED | - not sorted by row (default)
| MAT_COLUMNS_SORTED | - sorted by column
| MAT_COLUMNS_UNSORTED | - not sorted by column (default)

Not these options reflect the data you pass in with MatSetValues(); it has nothing to do with how the data is stored internally in the matrix data structure.

When (re)assembling a matrix, we can restrict the input for efficiency/debugging purposes. These options include

| MAT_NO_NEW_NONZERO_LOCATIONS | - additional insertions will not be allowed if they generate a new nonzero
| MAT_YES_NEW_NONZERO_LOCATIONS | - additional insertions will be allowed
| MAT_NO_NEW_DIAGONALS | - additional insertions will not be allowed if they generate a nonzero in a new diagonal (for block diagonal format only)
| MAT_YES_NEW_DIAGONALS | - new diagonals will be allowed (for block diagonal format only)
| MAT_IGNORE_OFF_PROC_ENTRIES | - drops off-processor entries
| MAT_NEW_NONZERO_LOCATION_ERR | - generates an error for new matrix entry
| MAT_USE_HASH_TABLE | - uses a hash table to speed up matrix assembly

### Notes

Some options are relevant only for particular matrix types and are thus ignored by others. Other options are not supported by certain matrix types and will generate an error message if set.

If using a Fortran 77 module to compute a matrix, one may need to use the column-oriented option (or convert to the row-oriented format).

MAT_NO_NEW_NONZERO_LOCATIONS indicates that any add or insertion that would generate a new entry in the nonzero structure is instead ignored. Thus, if memory has not alredy been allocated for this particular data, then the insertion is ignored. For dense matrices, in which the entire array is allocated, no entries are ever ignored. Set after the first MatAssemblyEnd()

MAT_NEW_NONZERO_LOCATION_ERR indicates that any add or insertion that would generate a new entry in the nonzero structure instead produces an error. (Currently supported for AIJ and BAIJ formats only.) This is a useful flag when using SAME_NONZERO_PATTERN in calling KSPSetOperators() to ensure that the nonzero pattern truely does remain unchanged. Set after the first MatAssemblyEnd()

MAT_NEW_NONZERO_ALLOCATION_ERR indicates that any add or insertion that would generate a new entry that has not been preallocated will instead produce an error. (Currently supported for AIJ and BAIJ formats only.) This is a useful flag when debugging matrix memory preallocation.

MAT_IGNORE_OFF_PROC_ENTRIES indicates entries destined for other processors should be dropped, rather than stashed. This is useful if you know that the "owning" processor is also always generating the correct matrix entries, so that PETSc need not transfer duplicate entries generated on another processor.

MAT_USE_HASH_TABLE indicates that a hash table be used to improve the searches during matrix assembly. When this flag is set, the hash table is created during the first Matrix Assembly. This hash table is used the next time through, during MatSetVaules()/MatSetVaulesBlocked() to improve the searching of indices. MAT_NO_NEW_NONZERO_LOCATIONS flag should be used with MAT_USE_HASH_TABLE flag. This option is currently supported by MATMPIBAIJ format only.

MAT_KEEP_ZEROED_ROWS indicates when MatZeroRows() is called the zeroed entries are kept in the nonzero structure

MAT_IGNORE_ZERO_ENTRIES - for AIJ/IS matrices this will stop zero values from creating a zero location in the matrix

MAT_USE_INODES - indicates using inode version of the code - works with AIJ and ROWBS matrix types

MAT_DO_NOT_USE_INODES - indicates not using inode version of the code - works with AIJ and ROWBS matrix types (database option "-mat_no_inode")

Level:intermediate
Location:src/mat/interface/matrix.c
Index of all Mat routines
Table of Contents for all manual pages
Index of all manual pages

### Examples

src/mat/examples/tutorials/ex5.c.html
src/ksp/ksp/examples/tutorials/ex5.c.html
src/ksp/ksp/examples/tutorials/ex9.c.html
src/snes/examples/tutorials/ex5.c.html
src/snes/examples/tutorials/ex14.c.html
src/snes/examples/tutorials/ex5f90.F.html
src/ts/examples/tutorials/ex2.c.html
src/ts/examples/tutorials/ex3.c.html
src/ts/examples/tutorials/ex4.c.html
src/ts/examples/tutorials/ex5.c.html
src/ts/examples/tutorials/ex6.c.html