[petsc-users] Why use MATMPIBAIJ?

Jed Brown jed at jedbrown.org
Thu Jan 14 12:57:37 CST 2016

Hoang Giang Bui <hgbk2008 at gmail.com> writes:
> One more question I like to ask, which is more on the performance of the
> solver. That if I have a coupled problem, says the point block is [u_x u_y
> u_z p] in which entries of p block in stiffness matrix is in a much smaller
> scale than u (p~1e-6, u~1e+8), then AMG with hypre in PETSc still scale?

You should scale the model (as Barry says).  But the names of your
variables suggest that the system is a saddle point problem, in which
case there's a good chance AMG won't work at all.  For example,
BoomerAMG produces a singular preconditioner in similar contexts, such
that the preconditioned residual drops smoothly while the true residual
stagnates (the equations are not solved at all).  So be vary careful if
you think it's "working".
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