[petsc-users] Slepc Matrix memory preallocation

[Michael R Nowak]

Hello,

I'm setting up a matrix with Slepc, and manually setting the preallocation
for nonzero entries row-by-row using the MatMPISBAIJSetPreallocation
function as follows:

MatMPISBAIJSetPreallocation(LaplaceOperator,
                            1,
                            0,
                            nonzeroEntries,
                            0,
                            PETSC_NULL);

The problem with this is that the number of nonzero entries per row that I
give Slepc is not the same as the number of nonzero entries that Slepc
allocates space for, slepc always seems to allocate N more nonzeroes than
needed, with N being the number of rows in the matrix. This is a problem
for me, since I would like to reduce the number of unneeded nonzero entries
to exactly zero, in order to save memory. The number of nonzero entries
that I give in nonzeroEntries is exactly what is used, so why are extra
nonzeroes being allocated? Any help with this would be much appreciated.

Thanks,

Mike Nowak