Add a uniform coarsening algorithm

common/unified/CMakeLists.txt

@@ -21,6 +21,7 @@ set(UNIFIED_SOURCES
     matrix/diagonal_kernels.cpp
     multigrid/pgm_kernels.cpp
     multigrid/rs_kernels.cpp
+    multigrid/uniform_coarsening_kernels.cpp
     preconditioner/jacobi_kernels.cpp
     solver/bicg_kernels.cpp
     solver/bicgstab_kernels.cpp

common/unified/multigrid/uniform_coarsening_kernels.cpp

@@ -0,0 +1,63 @@
+// SPDX-FileCopyrightText: 2017 - 2026 The Ginkgo authors
+//
+// SPDX-License-Identifier: BSD-3-Clause
+
+#include "core/multigrid/uniform_coarsening_kernels.hpp"
+
+#include <ginkgo/core/base/math.hpp>
+
+#include "common/unified/base/kernel_launch.hpp"
+#include "common/unified/base/kernel_launch_reduction.hpp"
+#include "core/components/prefix_sum_kernels.hpp"
+
+
+namespace gko {
+namespace kernels {
+namespace GKO_DEVICE_NAMESPACE {
+namespace uniform_coarsening {
+
+
+template <typename ValueType, typename IndexType>
+void fill_restrict_op(std::shared_ptr<const DefaultExecutor> exec,
+                      const array<IndexType>* coarse_rows,
+                      matrix::Csr<ValueType, IndexType>* restrict_op)
+{
+    run_kernel(
+        exec,
+        [] GKO_KERNEL(auto tidx, const auto coarse_data,
+                      auto restrict_col_idxs) {
+            if (coarse_data[tidx] >= 0) {
+                restrict_col_idxs[coarse_data[tidx]] = tidx;
+            }
+        },
+        coarse_rows->get_size(), coarse_rows->get_const_data(),
+        restrict_op->get_col_idxs());
+}
+
+GKO_INSTANTIATE_FOR_EACH_VALUE_AND_INDEX_TYPE(
+    GKO_DECLARE_UNIFORM_COARSENING_FILL_RESTRICT_OP);
+
+
+template <typename IndexType>
+void fill_incremental_indices(std::shared_ptr<const DefaultExecutor> exec,
+                              size_type coarse_skip,
+                              array<IndexType>* coarse_rows)
+{
+    const size_type num_elems = coarse_rows->get_size();
+    const size_type num_iters = gko::ceildiv(num_elems, coarse_skip);
+    run_kernel(
+        exec,
+        [] GKO_KERNEL(auto tidx, auto coarse_skip, auto coarse_data) {
+            coarse_data[tidx * coarse_skip] = tidx;
+        },
+        num_iters, coarse_skip, coarse_rows->get_data());
+}
+
+GKO_INSTANTIATE_FOR_EACH_INDEX_TYPE(
+    GKO_DECLARE_UNIFORM_COARSENING_FILL_INCREMENTAL_INDICES);
+
+
+}  // namespace uniform_coarsening
+}  // namespace GKO_DEVICE_NAMESPACE
+}  // namespace kernels
+}  // namespace gko

core/CMakeLists.txt

@@ -97,6 +97,7 @@ target_sources(
         multigrid/fixed_coarsening.cpp
         multigrid/pgm.cpp
         multigrid/rs.cpp
+        multigrid/uniform_coarsening.cpp
         preconditioner/batch_jacobi.cpp
         preconditioner/gauss_seidel.cpp
         preconditioner/ic.cpp

core/config/config_helper.hpp

@@ -72,6 +72,7 @@ enum class LinOpFactoryType : int {
     Multigrid,
     Pgm,
     Rs,
+    UniformCoarsening,
     Schwarz
 };
 

core/config/multigrid_config.cpp

@@ -4,6 +4,7 @@
 
 #include <ginkgo/core/multigrid/pgm.hpp>
 #include <ginkgo/core/multigrid/rs.hpp>
+#include <ginkgo/core/multigrid/uniform_coarsening.hpp>
 
 #include "core/config/parse_macro.hpp"
 
@@ -14,6 +15,8 @@ namespace config {
 
 GKO_PARSE_VALUE_AND_INDEX_TYPE(Pgm, gko::multigrid::Pgm);
 GKO_PARSE_VALUE_AND_INDEX_TYPE(Rs, gko::multigrid::Rs);
+GKO_PARSE_VALUE_AND_INDEX_TYPE(UniformCoarsening,
+                               gko::multigrid::UniformCoarsening);
 
 
 }  // namespace config

core/config/registry.cpp

@@ -53,6 +53,8 @@ configuration_map generate_config_map()
             {"solver::Multigrid", parse<LinOpFactoryType::Multigrid>},
             {"multigrid::Pgm", parse<LinOpFactoryType::Pgm>},
             {"multigrid::Rs", parse<LinOpFactoryType::Rs>},
+            {"multigrid::UniformCoarsening",
+             parse<LinOpFactoryType::UniformCoarsening>},
 #if GINKGO_BUILD_MPI
         {
             "preconditioner::Schwarz", parse<LinOpFactoryType::Schwarz>

core/device_hooks/common_kernels.inc.cpp

@@ -53,6 +53,7 @@
 #include "core/matrix/sparsity_csr_kernels.hpp"
 #include "core/multigrid/pgm_kernels.hpp"
 #include "core/multigrid/rs_kernels.hpp"
+#include "core/multigrid/uniform_coarsening_kernels.hpp"
 #include "core/preconditioner/batch_jacobi_kernels.hpp"
 #include "core/preconditioner/isai_kernels.hpp"
 #include "core/preconditioner/jacobi_kernels.hpp"
@@ -1154,6 +1155,16 @@ GKO_STUB_VALUE_AND_INDEX_TYPE(GKO_DECLARE_RS_COMPUTE_INTERPOLATION_KERNEL);
 }  // namespace rs
 
 
+namespace uniform_coarsening {
+
+
+GKO_STUB_VALUE_AND_INDEX_TYPE(GKO_DECLARE_UNIFORM_COARSENING_FILL_RESTRICT_OP);
+GKO_STUB_INDEX_TYPE(GKO_DECLARE_UNIFORM_COARSENING_FILL_INCREMENTAL_INDICES);
+
+
+}  // namespace uniform_coarsening
+
+
 namespace set_all_statuses {