To avoid zero pivot error in IC/ILU preconditioners,  I plan to permute matrix before solving the linear system. I referred example ex10(https://petsc.org/main/src/ksp/ksp/tutorials/ex10.c.html) and ex18(https://petsc.org/main/src/ksp/ksp/tutorials/ex18.c.html), and was confused that why vector b is permuted by column permutation index set:

// in ex18.c

174:   if (permute) {
175:     Mat Aperm;
176:     MatGetOrdering(A, ordering, &rowperm, &colperm);
177:     MatPermute(A, rowperm, colperm, &Aperm);
178:     VecPermute(b, colperm, PETSC_FALSE);
179:     MatDestroy(&A);
180:     A = Aperm; /* Replace original operator with permuted version */
181:   }

Another question is why  MatReorderForNonzeroDiagonal function only works for type MATSEQAIJ? If it works for other matrix types, then this function will meet my requirement.

Thanks,

Xiaofeng