From b5e16444e4ec4980c65b9f60473ce10812ad053c Mon Sep 17 00:00:00 2001
From: Andreas Kloeckner <inform@tiker.net>
Date: Thu, 9 Feb 2017 10:27:58 -0600
Subject: [PATCH] Improve group-joined-mesh error message
---
meshmode/mesh/__init__.py | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/meshmode/mesh/__init__.py b/meshmode/mesh/__init__.py
index 6b65caf..413b79d 100644
--- a/meshmode/mesh/__init__.py
+++ b/meshmode/mesh/__init__.py
@@ -175,7 +175,9 @@ class MeshElementGroup(Record):
def join_mesh(self, element_nr_base, node_nr_base):
if self.element_nr_base is not None:
raise RuntimeError("this element group has already joined a mesh, "
- "cannot join another")
+ "cannot join another (The element group's element_nr_base "
+ "is already assigned, and that typically happens when a "
+ "group joins a Mesh instance.)")
return self.copy(
element_nr_base=element_nr_base,
--
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