extract_constant_modes fix

diff --git a/source/dofs/dof_tools.cc b/source/dofs/dof_tools.cc
index 55f4c3553c670499eaf539d9585df370cedf29a8..05b451da9395c09e22a0078908d5831bac77a13c 100644 (file)
--- a/source/dofs/dof_tools.cc
+++ b/source/dofs/dof_tools.cc
@@ -1265,6 +1265,14 @@ namespace DoFTools
                          const ComponentMask &           component_mask,
                          std::vector<std::vector<bool>> &constant_modes)
   {
+    // If there are no locally owned DoFs, return with an empty
+    // constant_modes object:
+    if (dof_handler.n_locally_owned_dofs() == 0)
+      {
+        constant_modes = std::vector<std::vector<bool>>(0);
+        return;
+      }
+
     const unsigned int n_components = dof_handler.get_fe(0).n_components();
     Assert(component_mask.represents_n_components(n_components),
            ExcDimensionMismatch(n_components, component_mask.size()));