[petsc-users] (no subject)

Jed Brown jed at jedbrown.org
Sun Dec 1 09:45:35 CST 2019

Mark Adams <mfadams at lbl.gov> writes:

> FM matrices are slow and meant for debugging mostly (I thought,
> although the docs just give this warning if coloring is not available).
> I would check the timings from -log_view and verify that the time is spent
> in MatFDColoringApply. Running with -info should print the number of colors
> (C). The cost of an FD matrix is about C x cost of an exact Jacobian.
> Roughly. You could check that.

This depends a lot on how efficient the residual and Jacobian evaluation
is.  We've seen examples where a colored Jacobian is less expensive than
analytic, even when the analytic is not "poorly written".

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