**petsc-3.9.4 2018-09-11**

# MatDiagonalSet

Computes Y = Y + D, where D is a diagonal matrix that is represented as a vector. Or Y[i,i] = D[i] if InsertMode is INSERT_VALUES.
### Synopsis

#include "petscmat.h"
PetscErrorCode MatDiagonalSet(Mat Y,Vec D,InsertMode is)

### Input Parameters

Neighbor-wise Collective on Mat and Vec

Notes: If the matrix Y is missing some diagonal entries this routine can be very slow. To make it fast one should initially
fill the matrix so that all diagonal entries have a value (with a value of zero for those locations that would not have an
entry).

### Keywords

matrix, add, shift, diagonal

### See Also

MatShift(), MatScale(), MatDiagonalScale()

### Level

intermediate

### Location

src/mat/utils/axpy.c
### Examples

src/ts/examples/tutorials/ex50.c.html

src/tao/pde_constrained/examples/tutorials/elliptic.c.html

### Implementations

MatDiagonalSet_MPIAIJ in src/mat/impls/aij/mpi/mpiaij.c

MatDiagonalSet_SeqAIJ in src/mat/impls/aij/seq/aij.c

MatDiagonalSet_IS in src/mat/impls/is/matis.c

MatDiagonalSet_MFFD in src/mat/impls/mffd/mffd.c

MatDiagonalSet_Nest in src/mat/impls/nest/matnest.c

MatDiagonalSet_MPISELL in src/mat/impls/sell/mpi/mpisell.c

MatDiagonalSet_Shell in src/mat/impls/shell/shell.c

Index of all Mat routines

Table of Contents for all manual pages

Index of all manual pages