The current model is a bit wonky.
At the first call to KSPSolve after a call to KSPSetComputeOperators the
computematrix, computerhs, and computeinitialguess are called.
In subsequent calls to KSPSolve ONLY the computerhs is called.
So for example
KSPSetComputeOperators()
KSPSolve -- computematrix, rhs, initial guess called
KSPSolve --- computerhs called
KSPSetComputerOperators()
KSPSolve -- computematrix, rhs, initial guess called
Note that the KSPSetCompute...() functions are just one particular way of
using KSP. You can also use the "standard" interface
Set values into matrix and rhs and initial guess (call
KSPSetInitialGuessNonzero)
KSPSolve(ksp,b,x)
change values in b, this would use the current values in x as the initial
guess for the next solve
KSPSolve(ksp,b,x)
change values in b and x
KSPSolve()
Change values in matrix and b and x (for initial guess)
KSPSolve()
This gives you exact detailed control over when and what you set in initial
guesses.
Is there a particular reason for your problem that it is better to use the
KSPSetCompute...() interface?
Barry
Note I wrote the KSPSetCompute...() interface so that PCMG could "build its
own" coarse grid matrix values without the user needing to set values for all
the levels before calling KSPSolve.
> On Oct 9, 2015, at 5:04 AM, Filippo Leonardi
> <[email protected]> wrote:
>
> So, I want to solve a system Ax = b multiple times, reuse A with different
> bs.
> It is natural to set differents initial guesses each time for iterative
> solvers.
>
> And
> KSPSetComputeInitialGuess(ksp,ComputeGuess,&user);
> is what PETSc provide for setting the Guess.
>
> I am unsure if I am making something wrong, but it seems to me that this
> function is called only once the matrix is first setted up. I want to be
> called each time.
>
> See my modified ex32.c for comparison.
>
> ./ex32 -pc_type mg -pc_mg_type full -ksp_type fgmres -ksp_monitor_short -
> pc_mg_levels 3 -mg_coarse_pc_factor_shift_type nonzero -
> ksp_initial_guess_nonzero
>
> Thanks.
>
> Best,
> Filippo<ex32.c>
