[petsc-users] Get and Set the k-th diagonal elements

[Barry Smith]

  How are you planning to use these diagonals? This might help us make suggestions as to what is a reasonable approach. Accessing diagonals is not a natural operation for sparse matrices stored by rows or columns.

   Barry



On May 6, 2011, at 3:56 PM, Xiangdong Liang wrote:

> Hello everyone,
> 
> I am wondering whether there is some function like MatGetDiagonal to
> get the k-th diagonal (above or below the main diagonal) of the matrix
> A. If I have to write my own function, what built-in function should I
> use to get a particular element of A? It seems that MatGetValues
> returns a block of matrix. I guess if I only extract one element once,
> it would not be efficient. Any suggestions? Thanks.
> 
> Best,
> Xiangdong