[petsc-users] get sub matrix from MPIBAIJ with MatCreateSubMatrix

[Smith, Barry F.]

> On Jul 26, 2018, at 10:34 AM, Xiangdong <epscodes at gmail.com> wrote:
> 
> Hello everyone,
> 
> I have a question about get the sub matrix Aodd from a MPIBAIJ matrix A. For example, if the bs=2 and the matrix size is 10x10. How can I get the 5x5 submatrix corresponding to the odd rows and odd columns only?
> 
> I tried to use the MatCreateSubMatrix, but get the error messages "Index set does not match blocks". It seems that MatCreateSubMatrix can only provide the whole block, instead of just a specific component of that block.
> 
> Can you give me some suggestions on extracting the submatrix corresponding to a specific component?

   Either create a AIJ matrix originally or use MatConvert to convert from BAIJ to AIJ and then use MatCreateSubMatrix(). Note that AIJ provides a great deal more flexibility with the utilities and solvers than BAIJ.

   Barry

> 
> Thank you.
> 
> Best,
> Xiangdong