fix tests/mpi/step-39

And yes, making a copy of the matrix was indeed a mistake here.

diff --git a/tests/mpi/step-39.cc b/tests/mpi/step-39.cc
index f9ee1d0ee1f38b53a3f23e0597936128ef1230c2..9180b959cf797362d412f8a90292d2d0b51c689c 100644 (file)
--- a/tests/mpi/step-39.cc
+++ b/tests/mpi/step-39.cc
@@ -563,7 +563,7 @@ namespace Step39
     SolverControl coarse_solver_control (1000, 1e-10, false, false);
     SolverCG<TrilinosWrappers::MPI::Vector> coarse_solver(coarse_solver_control);
     PreconditionIdentity identity;
-    TrilinosWrappers::SparseMatrix coarse_matrix = mg_matrix[0];
+    TrilinosWrappers::SparseMatrix & coarse_matrix = mg_matrix[0];
     MGCoarseGridLACIteration<SolverCG<TrilinosWrappers::MPI::Vector>,TrilinosWrappers::MPI::Vector>
     coarse_grid_solver(coarse_solver, coarse_matrix, identity);