Add a mixed precision example

examples/CMakeLists.txt

@@ -31,6 +31,7 @@ add_amgcl_example(schur_pressure_correction schur_pressure_correction.cpp)
 add_amgcl_example(cpr cpr.cpp)
 add_amgcl_example(cpr_drs cpr_drs.cpp)
 add_amgcl_example(custom_adapter custom_adapter.cpp)
+add_amgcl_example(mixed_precision mixed_precision.cpp)
 
 add_amgcl_example(ublas ublas.cpp)
 target_link_libraries(ublas ${Boost_SERIALIZATION_LIBRARY})

examples/mixed_precision.cpp

@@ -0,0 +1,65 @@
+#include <vector>
+#include <tuple>
+
+#include <amgcl/adapter/crs_tuple.hpp>
+#include <amgcl/backend/builtin.hpp>
+#include <amgcl/amg.hpp>
+#include <amgcl/coarsening/smoothed_aggregation.hpp>
+#include <amgcl/relaxation/spai0.hpp>
+#include <amgcl/solver/cg.hpp>
+#include <amgcl/profiler.hpp>
+
+#include "sample_problem.hpp"
+
+namespace amgcl { profiler<> prof; }
+using amgcl::prof;
+
+int main() {
+    // Combine single-precision preconditioner with a
+    // double-precision Krylov solver.
+    typedef
+        amgcl::amg<
+            amgcl::backend::builtin<float>,
+            amgcl::coarsening::smoothed_aggregation,
+            amgcl::relaxation::spai0
+            >
+        Precond;
+
+    // Solver is in double precision:
+    typedef
+        amgcl::solver::cg<
+            amgcl::backend::builtin<double>
+            >
+        Solver;
+
+    std::vector<int>    ptr, col;
+    std::vector<double> val_d;
+    std::vector<double> rhs;
+
+    prof.tic("assemble");
+    int n = sample_problem(128, val_d, col, ptr, rhs);
+    prof.toc("assemble");
+
+    std::vector<double> x(n, 0.0);
+    std::vector<float>  val_f(val_d.begin(), val_d.end());
+
+    auto A_f = std::tie(n, ptr, col, val_f);
+    auto A_d = std::tie(n, ptr, col, val_d);
+
+    prof.tic("setup");
+    Solver S(n);
+    Precond P(A_f);
+    prof.toc("setup");
+
+    std::cout << P << std::endl;
+
+    int iters;
+    double error;
+    prof.tic("solve");
+    std::tie(iters, error) = S(A_d, P, rhs, x);
+    prof.toc("solve");
+
+    std::cout << "Iterations: " << iters << std::endl
+              << "Error:      " << error << std::endl
+              << prof << std::endl;
+}