Improve an error message.

git-svn-id: https://svn.dealii.org/trunk@32075 0785d39b-7218-0410-832d-ea1e28bc413d

diff --git a/deal.II/source/numerics/matrix_tools.cc b/deal.II/source/numerics/matrix_tools.cc
index 74f5dcbba1125adf8d294bd537ab7aef22b245e0..6a726729c127a62bb53e14b7e8c6616667c20e93 100644 (file)
--- a/deal.II/source/numerics/matrix_tools.cc
+++ b/deal.II/source/numerics/matrix_tools.cc
@@ -2033,7 +2033,11 @@ namespace MatrixTools
                 Assert ((p != matrix.end(row))
                         &&
                         (p->column() == dof_number),
-                        ExcInternalError());
+                        ExcMessage("This function is trying to access an element of the "
+                            "matrix that doesn't seem to exist. Are you using a "
+                            "nonsymmetric sparsity pattern? If so, you are not "
+                            "allowed to set the eliminate_column argument of this "
+                            "function, see the documentation."));
 
                 // correct right hand side
                 right_hand_side(row) -= p->value() /