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GMRES/MLMG: Set the number of MG V-cycles per GMRES iteration #3875

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merged 1 commit into from May 9, 2024
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GMRES/MLMG: Set the number of MG V-cycles per GMRES iteration #3875

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27 changes: 21 additions & 6 deletions Src/LinearSolvers/AMReX_GMRES_MLMG.H
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Expand Up @@ -91,14 +91,19 @@ public:

void precond (MF& lhs, MF const& rhs) const;

//! Control whether or not to use MLMG as preconditioner.
bool usePrecond (bool new_flag) { return std::exchange(m_use_precond, new_flag); }

//! Set the number of MLMG preconditioner iterations per GMRES iteration.
void setPrecondNumIters (int precond_niters) { m_precond_niters = precond_niters; }

private:
GM m_gmres;
MG* m_mlmg;
MLLinOpT<MF>* m_linop;
bool m_use_precond = true;
bool m_prop_zero = false;
int m_precond_niters = 1;
};

template <typename MF>
Expand Down Expand Up @@ -184,12 +189,22 @@ void GMRESMLMGT<MF>::precond (MF& lhs, MF const& rhs) const
if (m_use_precond) {
m_mlmg->prepareMGcycle();

LocalCopy(m_mlmg->res[0][0], rhs, 0, 0, nComp(rhs), IntVect(0));

m_mlmg->mgVcycle(0,0);

LocalCopy(lhs, m_mlmg->cor[0][0], 0, 0, nComp(rhs), IntVect(0));

for (int icycle = 0; icycle < m_precond_niters; ++icycle) {
if (icycle == 0) {
LocalCopy(m_mlmg->res[0][0], rhs, 0, 0, nComp(rhs), IntVect(0));
} else {
m_mlmg->computeResOfCorrection(0,0);
LocalCopy(m_mlmg->res[0][0], m_mlmg->rescor[0][0], 0, 0, nComp(rhs), IntVect(0));
}

m_mlmg->mgVcycle(0,0);

if (icycle == 0) {
LocalCopy(lhs, m_mlmg->cor[0][0], 0, 0, nComp(rhs), IntVect(0));
} else {
increment(lhs, m_mlmg->cor[0][0], RT(1));
}
}
} else {
LocalCopy(lhs, rhs, 0, 0, nComp(lhs), IntVect(0));
}
Expand Down
1 change: 1 addition & 0 deletions Tests/LinearSolvers/CurlCurl/MyTest.H
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Expand Up @@ -32,6 +32,7 @@ private:

bool use_gmres = false;
bool gmres_use_precond = true;
int gmres_precond_niters = 1;

amrex::Geometry geom;
amrex::BoxArray grids;
Expand Down
2 changes: 2 additions & 0 deletions Tests/LinearSolvers/CurlCurl/MyTest.cpp
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Expand Up @@ -62,6 +62,7 @@ MyTest::solve ()
{
GMRESMLMGT<V> gmsolver(mlmg);
gmsolver.usePrecond(gmres_use_precond);
gmsolver.setPrecondNumIters(gmres_precond_niters);

// This system has homogeneous BC unlike
// Tests/LinearSolvers/ABecLaplacian_C, so the setup is simpler.
Expand Down Expand Up @@ -106,6 +107,7 @@ MyTest::readParameters ()

pp.query("use_gmres", use_gmres);
pp.query("gmres_use_precond", gmres_use_precond);
pp.query("gmres_precond_niters", gmres_precond_niters);

pp.query("beta_factor", beta_factor);
pp.query("alpha", alpha);
Expand Down