> On Jun 5, 2018, at 7:36 PM, Matthew Overholt <[email protected]> wrote:
>
>
> On Tue, Jun 5, 2018 at 1:48 PM, Smith, Barry F. <[email protected]> wrote:
>
>
> > On Jun 5, 2018, at 4:08 PM, Matthew Overholt <[email protected]> wrote:
> >
> > Yes to Matthew - not repeating Phase 1: Fill-reduction analysis and
> > symbolic factorization . Numerical factoring is required because the
> > matrix values have changed (although only slightly) as well as the RHS.
> >
> > We are using KSPPREONLY with Picard iterations. Thank you, Barry, for the
> > KSP*Preconditioner calls I wasn't aware of.
> >
> > It sounds like PETSc and/or Pardiso automatically determines whether Phase
> > 1 is required or not, but if we want to force a new Phase 1 (such as in a
> > long unsteady run), then I suppose we could just destroy KSP and remake it.
>
> I'm confused. Yes PETSc will do a new analysis if the nonzero structure
> changes otherwise it will never do a new analysis.
>
> Is your nonzero structure changing?
>
> If you nonzero structure is not changing you have to do nothing.
>
> If the nonzero structure does change than the code needs to do a new
> analysis because the old factors (for the numerical part) cannot work with
> the new nonzero locations of the matrix.
>
> I really don't see why you have to do anything?
>
> Barry
>
> No, the nonzero structure never changes. Redoing the analysis is not
> required, in the sense that a solution can still be obtained without it;
> however, for long unsteady runs (with heat sources turning on and off) the
> matrix values change so much that, without redoing the analysis, more
> iterations are required to converge at each time step, resulting in a
> doubling of the total solve time compared to when the analysis is
> periodically redone. I don't know exactly what Pardiso is doing "under the
> hood" but that has been our experience.
Strange; I've never heard of this before, anyways,
You could trick it by "saying" that the nonzero structure has changed even
if it has not. The matrix struct has a field A->nonzerostate you could simply
increase this value by 1 (include #include <petsc/private/matimpl.h> to get
access to the field). Any time you change this value will trigger a new
analysis stage.
>
> Matt...
