Adding clarification for incompatible MPI stubs in both Trilinos and PETSc.

diff --git a/cmake/configure/configure_2_trilinos.cmake b/cmake/configure/configure_2_trilinos.cmake
index 0472228b2034217ce626208201c79401b9dc3eb4..7dfa69d9fca628bb8f57f7424f9ba2c75776bc31 100644 (file)
--- a/cmake/configure/configure_2_trilinos.cmake
+++ b/cmake/configure/configure_2_trilinos.cmake
@@ -109,12 +109,14 @@ MACRO(FEATURE_TRILINOS_FIND_EXTERNAL var)
     #
     IF( DEAL_II_WITH_TRILINOS AND DEAL_II_WITH_PETSC AND NOT DEAL_II_WITH_MPI )
       MESSAGE(STATUS "Incompatible configuration settings: "
-        "MPI must be enabled to use both Trilinos and PETSc."
+        "MPI must be enabled to use both Trilinos and PETSc, as both libraries "
+       "provide mutually incompatible MPI stubs."
         )
       SET(TRILINOS_ADDITIONAL_ERROR_STRING
         ${TRILINOS_ADDITIONAL_ERROR_STRING}
         "To enable both Trilinos and PETSc, deal.II must be configured with MPI "
-        "or enable one between Trilinos and PETSc removing MPI, but found:\n"
+        "or enable one between Trilinos and PETSc removing MPI. Both Trilinos and PETSc "
+       "provide mutually incompatible MPI stubs, but found:\n"
         "  DEAL_II_WITH_MPI = ${DEAL_II_WITH_MPI}\n"
         "  DEAL_II_WITH_TRILINOS = ${DEAL_II_WITH_TRILINOS}\n"
         "  DEAL_II_WITH_PETSC = ${DEAL_II_WITH_PETSC}\n"