[petsc-users] MatSolve in CG - PCPreSolve

De Groof, Vincent Frans Maria Vincent.De-Groof at uibk.ac.at
Tue Nov 11 06:27:24 CST 2014

Dear all,

I think I further pinpointed the problem to the PCPreSolve. Both mine, as well as Petsc's PCG call  PCPreSolve and enter the (pc->ops->presolve). But mine does not apply the presolve.

Do I need to activate the PCPreSolve manually when I have written a KSP that I've registered using KSPRegister?


Von: De Groof, Vincent Frans Maria
Gesendet: Montag, 10. November 2014 17:57
An: petsc-users at mcs.anl.gov
Betreff: MatSolve in CG

Dear all,

I am writing a few variations on the PCG algorithm. Starting with my own PCG implementation, I noticed that my routine is quite a bit slower (~20%). I think I tracked it down to the MatSolve calls in PCApply. I am using BDDC as the preconditioner.

In the Petsc PCG function, each PCApply calls the MatSolve 3 times. It also calls MatSolve once somewhere between calling KSPSolve and KSPSolve_CG (KSP_SetUp has been called before). So MatSolve is called 1+3*(# iterations) per KSPSolve. In my own PCG variation, the initial MatSolve is not called. But MatSolve is called 4 times in each iteration, so in total 4*(# iterations).

Where does this MatSolve in between KSPSolve and KSPSolve_CG come from? And how can I make my function use less MatSolve's?

I hope that I explained the problem clearly, and maybe this is a very trivial question.

kind regards,
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