Improve an error message.

diff --git a/source/lac/trilinos_sparse_matrix.cc b/source/lac/trilinos_sparse_matrix.cc
index 0167dfc8b7877a5076557e1bf1e4a303f90dcb5b..68718d448c3e2dbedf92de6734ad803de041cd8a 100644 (file)
--- a/source/lac/trilinos_sparse_matrix.cc
+++ b/source/lac/trilinos_sparse_matrix.cc
@@ -2215,7 +2215,12 @@ namespace TrilinosWrappers
                                         const_cast<Epetra_CrsMatrix &>(
                                           tmp_result.trilinos_matrix()));
 #  else
-      Assert("false", ExcMessage("This function requires EpetraExt."));
+      Assert("false",
+             ExcMessage("This function requires that the Trilinos "
+                        "installation found while running the deal.II "
+                        "CMake scripts contains the optional Trilinos "
+                        "package 'EpetraExt'. However, this optional "
+                        "part of Trilinos was not found."));
 #  endif
       result.reinit(tmp_result.trilinos_matrix());
     }