From a84a10c005b5b6975c436bce2817e0f8227b546f Mon Sep 17 00:00:00 2001
From: tcclevenger <tcleven@clemson.edu>
Date: Wed, 15 Apr 2020 14:04:18 -0400
Subject: [PATCH] extract_constant_modes fix

---
 source/dofs/dof_tools.cc | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/source/dofs/dof_tools.cc b/source/dofs/dof_tools.cc
index 55f4c3553c..05b451da93 100644
--- 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()));
-- 
2.39.5