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

[Denis Davydov]

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.

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?
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.

Kind regards,
Denis.