[petsc-users] Question about MatMultDiagonalBlock

[John Fettig]

In mpiaij.c, there is this if statement:

   if (a->inode.size) mat->ops->multdiagonalblock = MatMultDiagonalBlock_MPIAIJ;

which prevents the operation MatMultDiagonalBlock from being set if
a->inode.size is zero.  Why is this?  What is wrong with the diagonal
block when inode.size==0?

Thanks,
John