Improve an error message and provide guidance.

In response to a recent question on the mailing list.

diff --git a/source/fe/fe_q.cc b/source/fe/fe_q.cc
index 6ffdaf1f59f79a515aae547faf6e90d6b2dba031..fe8fd248ed5aee6c927ceb0bb3ad56f6b2c68eac 100644 (file)
--- a/source/fe/fe_q.cc
+++ b/source/fe/fe_q.cc
@@ -36,7 +36,9 @@ FE_Q<dim,spacedim>::FE_Q (const unsigned int degree)
 {
   Assert (degree > 0,
           ExcMessage ("This element can only be used for polynomial degrees "
-                      "greater than zero"));
+                      "greater than zero. If you want an element of polynomial "
+                      "degree zero, then it cannot be continuous and you "
+                      "will want to use FE_DGQ<dim>(0)."));
   std::vector<Point<1> > support_points_1d(degree+1);
   for (unsigned int i=0; i<=degree; ++i)
     support_points_1d[i][0] = static_cast<double>(i)/degree;