[petsc-users] Zero entries of a sparse matrix in a block-wise style

[Jed Brown]

Mingchang Ding <dmcvamos at udel.edu> writes:

>> It appears that you are calling MatZeroRows with rows = {0, info.mx-1},
>> which will only affect the first and last rows.  The other entries are
>> how you have assembled them (with the matrix-matrix product).
>
> Yes. I think so. Is there anyway I can fill in the rows array with all the first and last DOF rows index efficiently instead of only filling in one row index at one time?

for (dof=0; dof<info.dof; dof++) rows[nrows++] = j*info.dof + dof;

(make sure to allocate the rows[] array to be large enough.