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[WIP] BCGSTAB: return the iterate with the smallest residual #2933

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[WIP] BCGSTAB: return the iterate with the smallest residual #2933

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BCGSTAB: return the iterate with the smallest residual
bigfooted Sep 27, 2026
e08ba03
clang
bigfooted Sep 27, 2026
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5 changes: 3 additions & 2 deletions Common/include/linear_algebra/CSysSolve.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -109,8 +109,9 @@ class CSysSolve {
mutable VectorType p; /*!< \brief Direction in CG and BCGSTAB. */
mutable VectorType z; /*!< \brief Preconditioned residual/direction in CG/BCGSTAB. */

mutable VectorType r_0; /*!< \brief The "arbitrary" vector in BCGSTAB. */
mutable VectorType v; /*!< \brief BCGSTAB "v" vector (v = A * M^-1 * p). */
mutable VectorType r_0; /*!< \brief The "arbitrary" vector in BCGSTAB. */
mutable VectorType v; /*!< \brief BCGSTAB "v" vector (v = A * M^-1 * p). */
mutable VectorType x_best; /*!< \brief BCGSTAB iterate with the smallest residual. */

mutable bool ritz_failed = false;
mutable unsigned long k = 0, k_new = 0;
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14 changes: 14 additions & 0 deletions Common/src/linear_algebra/CSysSolve.cpp
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Expand Up @@ -1087,6 +1087,7 @@ unsigned long CSysSolve<ScalarType>::BCGSTAB_LinSolver(const CSysVector<ScalarTy
p.Initialize(nBlk, nBlkDomain, nVar, nullptr);
v.Initialize(nBlk, nBlkDomain, nVar, nullptr);
z.Initialize(nBlk, nBlkDomain, nVar, nullptr);
x_best.Initialize(nBlk, nBlkDomain, nVar, nullptr);

bcg_ready = true;
}
Expand Down Expand Up @@ -1135,6 +1136,8 @@ unsigned long CSysSolve<ScalarType>::BCGSTAB_LinSolver(const CSysVector<ScalarTy
/*--- Initialization ---*/

ScalarType alpha = 1.0, omega = 1.0, rho = 1.0, rho_prime = 1.0;
ScalarType norm_best = norm_r;
x_best = x;
p = ScalarType(0.0);
v = ScalarType(0.0);
r_0 = r;
Expand Down Expand Up @@ -1195,6 +1198,10 @@ unsigned long CSysSolve<ScalarType>::BCGSTAB_LinSolver(const CSysVector<ScalarTy
/*--- Check if solution has converged, else output the relative residual if necessary ---*/

norm_r = r.norm();
if (norm_r < norm_best) {
norm_best = norm_r;
x_best = x;
}
if (norm_r < tol * norm0) break;
if (((monitoring) && (masterRank)) && ((i + 1) % monitorFreq == 0)) {
SU2_OMP_MASTER
Expand All @@ -1204,6 +1211,13 @@ unsigned long CSysSolve<ScalarType>::BCGSTAB_LinSolver(const CSysVector<ScalarTy
}
}

/*--- BCGSTAB does not reduce the residual monotonically, return the best iterate. ---*/

if ((config->GetComm_Level() == COMM_FULL) && (norm_r > norm_best)) {
x = x_best;
norm_r = norm_best;
}

/*--- Recalculate final residual (this should be optional) ---*/

if ((monitoring) && (config->GetComm_Level() == COMM_FULL)) {
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