[petsc-users] create PC, KSP, ST separately and use in EPS

[Jose E. Roman]

> El 29/10/2015, a las 13:32, Denis Davydov <davydden at gmail.com> escribió:
> 
> Dear all, 
> 
> I am currently looking at ways to extend deal.II PETSc/SLEPc wrappers classes to allow 
> specification of linear solvers and preconditioners to be used in SLEPc eigensolvers 
> using deal.II objects and NOT the command line arguments.

Yes, current deal.II wrappers for SLEPc are quite limited.

> 
> All examples and unit tests I came across in SLEPc work with EPSCreate() followed by 
> EPSGetST(), STGetKSP() and KSPGetPC(). This however does not fit well into object-oriented C++ code.
> Thus I plan to create each objects separately and pass them around.
> 
> I would like to ask if the way I see it (in terms of PETSc/SLEPc functions called) is conceptually correct:
> 
> — PETSc: Preconditioner class:
> PCCreate()
> PCSetType()
> PCSetFromOptions();
> —
> 
> — PETSc: Solver class (uses Preconditioner class):
> KSPCreate()
> KSPSetType()
> KSPSetPC() // set PC created above
> KSPSetConvergenceTest()
> KSPSetFromOptions()
> —
> 
> — SLEPc: SpectralTransformation class (uses Solver class)
> STCreate()
> STSetType()
> STSetShift() // some specific settings to transformation
> STSetKSP() // set KSP created above
> —
> 
> — SLEPc: Eigensolver class (uses SpectralTransformation class)
> EPSCreate()
> EPSSetTolerances()
> EPSSetConvergenceTest()
> EPSSetWhichEigenpairs()
> EPSSetProblemType()
> EPSSetType()
> EPSArnoldiSetDelayed() // any specific options to eigensolver
> EPSSetST() // set spectral transformation created above
> // solve
> EPSSetDimensions()
> EPSSetFromOptions()
> EPSSolve()
> —
> 
> Do this usage model sounds correct from SLEPc perspective?

I see no problem with this approach.

> What bothers me is that i do not call PCSetOperators()/PCSetUp() and KSPSetOperators()/KSPSetUp(), 
> which one would call while setting up PETSc objects to solve SLAE.
> Nonetheless I assume those functions are executed somewhere inside SLEPc depending on
> SHEP/GHEP and ST to be used.

Correct, EPS/ST handle the KSP coefficient matrix so KSPSetUp() must be done at EPSSetUp() and not before.

Jose

> 
> Kind regards,
> Denis.