[petsc-users] How to get number of local nonzeros of a matrix?

[Barry Smith]

On Dec 29, 2011, at 1:28 PM, Junchao Zhang wrote:

> Hello,
>   I create a MPIAIJ matrix.  How can I know the # of nonzeros stored locally? 

   MatGetInfo()

>   Furthermore, in case it is needed, how can I get access to the Compress Sparse Row(CSR) data structure of the local matrix, i.e., the row pointer array, column index array, value array?

   PETSc MPIAIJ matrices are not actually stored as a single CSR matrix on each process. They are actually stored as two CSR matrices: the "block diagonal local portion" and the "off-processor portion" (which is complicated by remapping the column indices). Thus it is basically impossible for normal PETSc users to muck directly with the matrix entries. If you are interested in developing new matrix entry specific solvers that work directly with MPIAIJ matrices then you need to include the private include files that define the data structures (you can find them in src/mat/impls/aij in subdirectories) I warn you that you need to be pretty good at C programming the muck with this stuff. 

   Barry



>   
>   Thank you!
> -- Junchao Zhang