# MatSetValuesStencil

Inserts or adds a block of values into a matrix. Using structured grid indexing

### Synopsis

    #include "petscmat.h"
    PetscErrorCode PETSCMAT_DLLEXPORT MatSetValuesStencil(Mat mat,PetscInt m,const MatStencil idxm[],PetscInt n,const MatStencil idxn[],const PetscScalar v[],InsertMode addv)

Not Collective

### Input Parameters

| mat | - the matrix
| v | - a logically two-dimensional array of values
| m | - number of rows being entered
| idxm | - grid coordinates (and component number when dof > 1) for matrix rows being entered
| n | - number of columns being entered
| idxn | - grid coordinates (and component number when dof > 1) for matrix columns being entered
| addv | - either ADD_VALUES or INSERT_VALUES, where ADD_VALUES adds values to any existing entries, and INSERT_VALUES replaces existing entries with new values

### Notes

By default the values, v, are row-oriented and unsorted. See MatSetOption() for other options.

Calls to MatSetValuesStencil() with the INSERT_VALUES and ADD_VALUES options cannot be mixed without intervening calls to the assembly routines.

The grid coordinates are across the entire grid, not just the local portion

MatSetValuesStencil() uses 0-based row and column numbers in Fortran as well as in C.

For setting/accessing vector values via array coordinates you can use the DAVecGetArray() routine

In order to use this routine you must either obtain the matrix with DAGetMatrix() or call MatSetLocalToGlobalMapping() and MatSetStencil() first.

The columns and rows in the stencil passed in MUST be contained within the ghost region of the given process as set with DACreateXXX() or MatSetStencil(). For example, if you create a DA with an overlap of one grid level and on a particular process its first local nonghost x logical coordinate is 6 (so its first ghost x logical coordinate is 5) the first i index you can use in your column and row indices in MatSetStencil() is 5.

In Fortran idxm and idxn should be declared as

        MatStencil idxm(4,m),idxn(4,n)

and the values inserted using

       idxm(MatStencil_i,1) = i

       idxm(MatStencil_j,1) = j

       idxm(MatStencil_k,1) = k

       idxm(MatStencil_c,1) = c

etc

Negative indices may be passed in idxm and idxn, these rows and columns are simply ignored. This allows easily inserting element stiffness matrices with homogeneous Dirchlet boundary conditions that you don't want represented in the matrix.

Inspired by the structured grid interface to the HYPRE package (http://www.llnl.gov/CASC/hypre)

### Efficiency Alert

The routine MatSetValuesBlockedStencil() may offer much better efficiency for users of block sparse formats (MATSEQBAIJ and MATMPIBAIJ).

### See Also

MatSetOption(), MatAssemblyBegin(), MatAssemblyEnd(), MatSetValuesBlocked(), MatSetValuesLocal()
MatSetValues(), MatSetValuesBlockedStencil(), MatSetStencil(), DAGetMatrix(), DAVecGetArray(), MatStencil

Level:beginner
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/examples/tutorials/ex22.c.html
src/ksp/examples/tutorials/ex25.c.html
src/ksp/examples/tutorials/ex28.c.html
src/ksp/examples/tutorials/ex29.c.html
src/ksp/examples/tutorials/ex22f.F.html
src/snes/examples/tutorials/ex5.c.html
src/snes/examples/tutorials/ex14.c.html
src/snes/examples/tutorials/ex18.c.html
src/snes/examples/tutorials/ex20.c.html