From: Martin Kronbichler Date: Tue, 19 Mar 2024 17:29:20 +0000 (+0100) Subject: SolverGMRES: Switch default orthogonalization strategy to delayed CGS2 X-Git-Tag: v9.6.0-rc1~472^2 X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=8d0715905415d7c3ebc71e16ac04fc1bd5c53df5;p=dealii.git SolverGMRES: Switch default orthogonalization strategy to delayed CGS2 --- diff --git a/doc/news/changes/incompatibilities/20240312Kronbichler b/doc/news/changes/incompatibilities/20240312Kronbichler index bcc4ad89e6..05c708e196 100644 --- a/doc/news/changes/incompatibilities/20240312Kronbichler +++ b/doc/news/changes/incompatibilities/20240312Kronbichler @@ -6,6 +6,9 @@ value of the basis size is now 30, compared to 28 used before. The old variable SolverGMRES::AdditionalData::max_n_tmp_vectors is still available, but whenever SolverGMRES::AdditionalData::max_basis_size is set to a non-zero value (including the value set by the default constructor), the latter takes -precedence. +precedence. Furthermore, the default algorithm has been changed from +the modified Gram-Schmidt algorithm to the classical Gram-Schmidt algorithm. +The latter uses unconditional reorthogonalization delayed by one step, +following the algorithm described in @cite Bielich2022.
-(Martin Kronbichler, 2024/04/12) +(Martin Kronbichler, 2024/03/12) diff --git a/doc/news/changes/minor/20240312Kronbichler b/doc/news/changes/minor/20240312Kronbichler index 77a5da56df..10d90b7d2b 100644 --- a/doc/news/changes/minor/20240312Kronbichler +++ b/doc/news/changes/minor/20240312Kronbichler @@ -6,4 +6,4 @@ SolverGMRES. Since the Arnoldi process is sensitive to roundoff errors, this change might slightly affect iteration counts (often giving slightly better results).
-(Martin Kronbichler, 2024/04/12) +(Martin Kronbichler, 2024/03/12) diff --git a/doc/news/changes/minor/20240319Kronbichler b/doc/news/changes/minor/20240319Kronbichler new file mode 100644 index 0000000000..e858a30194 --- /dev/null +++ b/doc/news/changes/minor/20240319Kronbichler @@ -0,0 +1,8 @@ +New: SolverGMRES and SolverFGMRES can now use an additional orthogonalization +strategy, controlled by +LinearAlgebra::OrthogonalizationStrategy::delayed_classical_gram_schmidt. This +implements the classical Gram-Schmidt method with delayed reorthogonalization, +a low-synchronization algorithm (performing one global reduction per GMRES +iteration for deal.II's own vectors) that has excellent stability properties. +
+(Martin Kronbichler, 2024/03/19) diff --git a/include/deal.II/lac/solver_gmres.h b/include/deal.II/lac/solver_gmres.h index 667bb99a03..7229f3ce9c 100644 --- a/include/deal.II/lac/solver_gmres.h +++ b/include/deal.II/lac/solver_gmres.h @@ -358,17 +358,19 @@ public: * to the default residual, and re-orthogonalization only if * necessary. Also, the batched mode with reduced functionality to track * information is disabled by default. Finally, the default - * orthogonalization algorithm is the modified Gram-Schmidt method. + * orthogonalization algorithm is the classical Gram-Schmidt method with + * delayed reorthogonalization, which combines stability with fast + * execution, especially in parallel. */ - explicit AdditionalData( - const unsigned int max_basis_size = 30, - const bool right_preconditioning = false, - const bool use_default_residual = true, - const bool force_re_orthogonalization = false, - const bool batched_mode = false, - const LinearAlgebra::OrthogonalizationStrategy - orthogonalization_strategy = - LinearAlgebra::OrthogonalizationStrategy::modified_gram_schmidt); + explicit AdditionalData(const unsigned int max_basis_size = 30, + const bool right_preconditioning = false, + const bool use_default_residual = true, + const bool force_re_orthogonalization = false, + const bool batched_mode = false, + const LinearAlgebra::OrthogonalizationStrategy + orthogonalization_strategy = + LinearAlgebra::OrthogonalizationStrategy:: + delayed_classical_gram_schmidt); /** * Maximum number of temporary vectors. Together with max_basis_size, this diff --git a/tests/lac/gmres_reorthogonalize_01.cc b/tests/lac/gmres_reorthogonalize_01.cc index 78a5b995a0..204feebe09 100644 --- a/tests/lac/gmres_reorthogonalize_01.cc +++ b/tests/lac/gmres_reorthogonalize_01.cc @@ -15,7 +15,7 @@ // tests that GMRES builds an orthonormal basis properly for a few difficult // test matrices. In particular, this test monitors when re-orthogonalization -// kicks in. +// kicks in for the modified Gram-Schmidt algorithm. #include #include @@ -70,6 +70,8 @@ test(unsigned int variant, unsigned int min_convergence_steps) SolverControl control(1000, 1e2 * std::numeric_limits::epsilon()); typename SolverGMRES>::AdditionalData data; data.max_basis_size = 80; + data.orthogonalization_strategy = + LinearAlgebra::OrthogonalizationStrategy::modified_gram_schmidt; SolverGMRES> solver(control, data); auto print_re_orthogonalization = [](int accumulated_iterations) { diff --git a/tests/lac/gmres_reorthogonalize_02.cc b/tests/lac/gmres_reorthogonalize_02.cc index 572485a7e6..576b9765d5 100644 --- a/tests/lac/gmres_reorthogonalize_02.cc +++ b/tests/lac/gmres_reorthogonalize_02.cc @@ -44,6 +44,8 @@ test() SolverControl control(1000, 1e3 * std::numeric_limits::epsilon()); typename SolverGMRES>::AdditionalData data; data.max_basis_size = 200; + data.orthogonalization_strategy = + LinearAlgebra::OrthogonalizationStrategy::modified_gram_schmidt; SolverGMRES> solver(control, data); auto print_re_orthogonalization = [](int accumulated_iterations) { diff --git a/tests/lac/gmres_reorthogonalize_03.cc b/tests/lac/gmres_reorthogonalize_03.cc index bccc1a3524..9f441b6385 100644 --- a/tests/lac/gmres_reorthogonalize_03.cc +++ b/tests/lac/gmres_reorthogonalize_03.cc @@ -69,6 +69,8 @@ test(unsigned int variant) typename SolverGMRES>::AdditionalData data; data.max_basis_size = 80; data.force_re_orthogonalization = true; + data.orthogonalization_strategy = + LinearAlgebra::OrthogonalizationStrategy::modified_gram_schmidt; SolverGMRES> solver(control, data); auto print_re_orthogonalization = [](int accumulated_iterations) { diff --git a/tests/lac/gmres_reorthogonalize_04.cc b/tests/lac/gmres_reorthogonalize_04.cc index fd41939e92..883f84124e 100644 --- a/tests/lac/gmres_reorthogonalize_04.cc +++ b/tests/lac/gmres_reorthogonalize_04.cc @@ -74,6 +74,8 @@ test(const unsigned int n_expected_steps) SolverControl control(1000, 1e3 * std::numeric_limits::epsilon()); typename SolverGMRES>::AdditionalData data; data.max_basis_size = 200; + data.orthogonalization_strategy = + LinearAlgebra::OrthogonalizationStrategy::modified_gram_schmidt; SolverGMRES> solver(control, data); auto print_re_orthogonalization = [](int accumulated_iterations) { diff --git a/tests/lac/gmres_reorthogonalize_05.cc b/tests/lac/gmres_reorthogonalize_05.cc index 37774657d8..a251c0d7da 100644 --- a/tests/lac/gmres_reorthogonalize_05.cc +++ b/tests/lac/gmres_reorthogonalize_05.cc @@ -72,6 +72,8 @@ test() typename SolverGMRES>::AdditionalData data; data.max_basis_size = 200; data.force_re_orthogonalization = true; + data.orthogonalization_strategy = + LinearAlgebra::OrthogonalizationStrategy::modified_gram_schmidt; SolverGMRES> solver(control, data); auto print_re_orthogonalization = [](int accumulated_iterations) {