Improve the M-matrix check in RS

Author: gojakuch

core/multigrid/rs.cpp

@@ -59,11 +59,14 @@ void Rs<ValueType, IndexType>::generate()
         this->set_fine_op(rs_op_shared_ptr);
     }
     array<bool> is_m_matrix_array(exec, 1);
-    exec->run(rs::make_check_m_matrix(rs_op, is_m_matrix_array));
-    if (!exec->copy_val_to_host(is_m_matrix_array.get_const_data())) {
-        GKO_NOT_SUPPORTED(
-            "RS coarsening requires an M-matrix (strictly positive diagonal, "
-            "non-positive off-diagonals).");
+    if (!parameters_.skip_m_matrix_check) {
+        exec->run(rs::make_check_m_matrix(rs_op, is_m_matrix_array));
+        if (!exec->copy_val_to_host(is_m_matrix_array.get_const_data())) {
+            GKO_NOT_SUPPORTED(
+                "RS coarsening requires an M-matrix (strictly positive "
+                "diagonal, "
+                "non-positive off-diagonals).");
+        }
     }
 
     // define arrays

include/ginkgo/core/multigrid/rs.hpp

@@ -78,6 +78,8 @@ class Rs : public EnableLinOp<Rs<ValueType, IndexType>>,
             strength_threshold, 0.25);
 
         bool GKO_FACTORY_PARAMETER_SCALAR(skip_sorting, false);
+
+        bool GKO_FACTORY_PARAMETER_SCALAR(skip_m_matrix_check, false);
     };
     GKO_ENABLE_LIN_OP_FACTORY(Rs, parameters, Factory);
     GKO_ENABLE_BUILD_METHOD(Factory);

reference/multigrid/rs_kernels.cpp

@@ -34,7 +34,7 @@ void check_m_matrix(std::shared_ptr<const ReferenceExecutor> exec,
     const auto col_idxs = matrix->get_const_col_idxs();
     const auto values = matrix->get_const_values();
 
-    bool is_m_matrix = true;
+    auto is_m_matrix = is_m_matrix_array.get_data();
 
     for (size_type row = 0; row < num_rows; ++row) {
         bool has_diag = false;
@@ -46,27 +46,22 @@ void check_m_matrix(std::shared_ptr<const ReferenceExecutor> exec,
             if (row == col) {
                 has_diag = true;
                 if (val <= 0.0) {
-                    is_m_matrix = false;
-                    break;
+                    *is_m_matrix = false;
+                    return;
                 }
             } else {
                 if (val > 0.0) {
-                    is_m_matrix = false;
-                    break;
+                    *is_m_matrix = false;
+                    return;
                 }
             }
         }
 
         if (!has_diag) {
-            is_m_matrix = false;
-        }
-
-        if (!is_m_matrix) {
-            break;
+            *is_m_matrix = false;
+            return;
         }
     }
-
-    is_m_matrix_array.get_data()[0] = is_m_matrix;
 }
 
 GKO_INSTANTIATE_FOR_EACH_VALUE_AND_INDEX_TYPE(