petsc-3.7.1 2016-05-15
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# MatZeroRows

Zeros all entries (except possibly the main diagonal) of a set of rows of a matrix.

### Synopsis

    #include "petscmat.h"
    PetscErrorCode MatZeroRows(Mat mat,PetscInt numRows,const PetscInt rows[],PetscScalar diag,Vec x,Vec b)

Collective on Mat Many br

### Input Parameters

| mat | - the matrix Many br
| numRows | - the number of rows to remove Many br
| rows | - the global row indices Many br
| diag | - value put in all diagonals of eliminated rows (0.0 will even eliminate diagonal entry) Many br
| x | - optional vector of solutions for zeroed rows (other entries in vector are not used) Many br
| b | - optional vector of right hand side, that will be adjusted by provided solution Many br

### Notes

For the AIJ and BAIJ matrix formats this removes the old nonzero structure, Many brbut does not release memory. For the dense and block diagonal Many brformats this does not alter the nonzero structure. Many br

If the option MatSetOption(mat,MAT_KEEP_NONZERO_PATTERN,PETSC_TRUE) the nonzero structure Many brof the matrix is not changed (even for AIJ and BAIJ matrices) the values are Many brmerely zeroed. Many br

The user can set a value in the diagonal entry (or for the AIJ and Many brrow formats can optionally remove the main diagonal entry from the Many brnonzero structure as well, by passing 0.0 as the final argument). Many br

For the parallel case, all processes that share the matrix (i.e., Many brthose in the communicator used for matrix creation) MUST call this Many brroutine, regardless of whether any rows being zeroed are owned by Many brthem. Many br

Each processor can indicate any rows in the entire matrix to be zeroed (i.e. each process does NOT have to Many brlist only rows local to itself). Many br

You can call MatSetOption(mat,MAT_NO_OFF_PROC_ZERO_ROWS,PETSC_TRUE) if each process indicates only rows it Many browns that are to be zeroed. This saves a global synchronization in the implementation. Many br

Many br

### See Also

MatZeroRowsIS(), MatZeroRowsStencil(), MatZeroEntries(), MatZeroRowsLocal(), MatSetOption()

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/ksp/ksp/examples/tutorials/ex3.c.html
src/ksp/ksp/examples/tutorials/ex10.c.html
src/ksp/ksp/examples/tutorials/ex49.c.html
src/ksp/ksp/examples/tutorials/ex51.c.html