SimplePetscNonlinearSolver.cpp

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#include <sstream>
#include "petscsnes.h"
#include "SimplePetscNonlinearSolver.hpp"
#include "Exception.hpp"
#include "PetscTools.hpp"

Vec SimplePetscNonlinearSolver::Solve(PetscErrorCode (*pComputeResidual)(SNES,Vec,Vec,void*),
#if (PETSC_VERSION_MAJOR==3 && PETSC_VERSION_MINOR>=5)
                                      PetscErrorCode (*pComputeJacobian)(SNES,Vec,Mat,Mat,void*),
#else
                                      PetscErrorCode (*pComputeJacobian)(SNES,Vec,Mat*,Mat*,MatStructure*,void*),
#endif
                                      Vec initialGuess,
                                      unsigned fill,
                                      void* pContext)
{
    SNES snes;

    // Create the residual vector by copying the structure of the initial guess
    Vec residual;
    VecDuplicate(initialGuess, &residual);

    Mat jacobian; // Jacobian Matrix
    PetscInt N; // number of elements

    // Get the size of the Jacobian from the residual
    VecGetSize(initialGuess, &N);

    // Note that the Jacobian matrix might involve new non-zero elements in the course of a SNES solve
    PetscTools::SetupMat(jacobian, N, N, fill, PETSC_DECIDE, PETSC_DECIDE, true, false /*malloc flag*/);

    SNESCreate(PETSC_COMM_WORLD, &snes);

    SNESSetFunction(snes, residual, pComputeResidual, pContext);
    SNESSetJacobian(snes, jacobian, jacobian, pComputeJacobian, pContext);

#if (PETSC_VERSION_MAJOR == 3 && PETSC_VERSION_MINOR >= 4) //PETSc 3.4 or later
    SNESSetType(snes, SNESNEWTONLS);
#else
    SNESSetType(snes, SNESLS);
#endif

    SNESSetTolerances(snes,1.0e-5,1.0e-5,1.0e-5,PETSC_DEFAULT,PETSC_DEFAULT);
#if (PETSC_VERSION_MAJOR == 3 && PETSC_VERSION_MINOR == 3) //PETSc 3.3
    SNESLineSearch linesearch;
    SNESGetSNESLineSearch(snes, &linesearch);
    SNESLineSearchSetType(linesearch, "bt"); //Use backtracking search as default
#elif (PETSC_VERSION_MAJOR == 3 && PETSC_VERSION_MINOR >= 4) //PETSc 3.4 or later
    SNESLineSearch linesearch;
    SNESGetLineSearch(snes, &linesearch);
    SNESLineSearchSetType(linesearch, "bt"); //Use backtracking search as default
#endif

    // x is the iteration vector SNES uses when solving, set equal to initialGuess to start with
    Vec x;

    VecDuplicate(initialGuess, &x);
    VecCopy(initialGuess, x);

#if (PETSC_VERSION_MAJOR == 3 && PETSC_VERSION_MINOR >= 5)
    // Seems to want the preconditioner to be explicitly set to none now
    // Copied this from the similar PETSc example at:
    // http://www.mcs.anl.gov/petsc/petsc-current/src/snes/examples/tutorials/ex1.c
    // Which got it to work...
    KSP ksp;
    SNESGetKSP(snes,&ksp);
    PC pc;
    KSPGetPC(ksp,&pc);
    PCSetType(pc,PCNONE);
#endif

#if (PETSC_VERSION_MAJOR == 2 && PETSC_VERSION_MINOR == 2) //PETSc 2.2
    SNESSolve(snes, x);
#else
    SNESSolve(snes, PETSC_NULL, x);
#endif
    PetscTools::Destroy(residual);
    PetscTools::Destroy(jacobian); // Free Jacobian

    SNESConvergedReason reason;
    SNESGetConvergedReason(snes,&reason);
// LCOV_EXCL_START
    if (reason < 0)
    {
        std::stringstream reason_stream;
        reason_stream << reason;
        PetscTools::Destroy(x); // Since caller can't free the memory in this case
        SNESDestroy(PETSC_DESTROY_PARAM(snes));
        EXCEPTION("Nonlinear Solver did not converge. PETSc reason code:"
                  +reason_stream.str()+" .");
    }
// LCOV_EXCL_STOP
    SNESDestroy(PETSC_DESTROY_PARAM(snes));

    return x;
}