fix trilinos warning

diff --git a/source/lac/trilinos_precondition_ml.cc b/source/lac/trilinos_precondition_ml.cc
index df79ff867b3396e50fe28a715e0339e819c04a1b..0b7d96eee9ee07e2daab73c2c517f33e1ac9e6c8 100644 (file)
--- a/source/lac/trilinos_precondition_ml.cc
+++ b/source/lac/trilinos_precondition_ml.cc
@@ -183,6 +183,7 @@ namespace TrilinosWrappers
     if (constant_modes_dimension > 0)
       {
         const size_type global_size = n_global_rows(matrix);
+        (void)global_length; // work around compiler warning about unused function in release mode
         Assert (global_size ==
                 static_cast<size_type>(global_length(distributed_constant_modes)),
                 ExcDimensionMismatch(global_size,