> Ooops, of course, this is what you are already doing. Sorry, haven't
> had coffee yet :-)
>
> But I still think there may be a way to tell PETSc to avoid
> recomputing the preconditioner at every timestep.
>
From the petsc manual:
"When solving multiple linear systems of the same size with the same
method, several options are available.
To solve successive linear systems having the same preconditioner matrix
(i.e., the same data structure
with exactly the same matrix elements) but different right-hand-side
vectors, the user should simply call
KSPSolve,() multiple times. The preconditioner setup operations (e.g.,
factorization for ILU) will be done
during the first call to KSPSolve() only; such operations will not be
repeated for successive solves.
To solve successive linear systems that have different
preconditioner matrices (i.e., the matrix elements
and/or the matrix data structure change), the user must call
KSPSetOperators() and KSPSolve() for each
solve. See Section 4.1 for a description of various flags for
KSPSetOperators() that can save work for such
cases."
Also, it says that in order to use LU, you should use the option
"-ksp_type preonly -pc_type lu"
- Dave
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