This usually isn't possible for iterative solvers and saves very little
for direct solvers (you still have to pay the factorization cost, but
can save a little on solve cost which is already vastly cheaper).
While it's easy to make the residual zero for some subset of unknowns,
that says nothing
Dear all,
I'm a PETSc user, solving some matrix equations using GMRES method. The
matrix is dense and huge, i.e. 10,000~100,000 unknowns. But I'm only
interested in the last six unknowns. Is it possible to accelerate the
convergence rate of them, even others are less accuracy.
Thanks.
Best,
