dolfin team mailing list archive

[Matthew Knepley <knepley@xxxxxxxxxxx>]

Johan Hoffman <hoffman@xxxxxxxxxxxxxxx> writes:
> > From my experience, solving time-dependent Navier-Stokes in 3d (linear
> elements on tetrahedrons), using PetSc both for inserting elements (as blocks) in assembling the "momentum matrix" and
> solving the resulting linear system with preconditioned GMRES, the amount of time spent on one assemble of the matrix
> can be roughly about 3 times the time for solving the system.
       I have experience with this. It does depend on the \Delta t, \nu
ratio for preconditioning. The assembly in my experience was only about
30% of the time. However, assembly is almost perfectly parallel, whereas
most preconditioners as worse (esp. with adpativity). Thus, the balance
also depends on scale. What this discussion shows I think, is that theory
is currently a very imperfect guide the performance of a code, leaving
large gaps for experiment, as Rob pointed out.

           Matt
> 
> /Johan
-- 
"Failure has a thousand explanations. Success doesn't need one" -- Sir Alec Guiness