PETSc version 3.15.5

PCPreSolve

Optional pre-solve phase, intended for any preconditioner-specific actions that must be performed before the iterative solve itself.

#include "petscksp.h" 
PetscErrorCode  PCPreSolve(PC pc,KSP ksp)

Collective on PC

	pc	- the preconditioner context
	ksp	- the Krylov subspace context

    PCPreSolve(pc,ksp);
    KSPSolve(ksp,b,x);
    PCPostSolve(pc,ksp);

The pre-solve phase is distinct from the PCSetUp() phase.

KSPSolve() calls this directly, so is rarely called by the user.

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