Augment the UMFPACK error message.

diff --git a/include/deal.II/lac/sparse_direct.h b/include/deal.II/lac/sparse_direct.h
index a3546365311580578c112a3b9758728fca685369..ee20a40124027cb9a026a5673e9096d666735778 100644 (file)
--- a/include/deal.II/lac/sparse_direct.h
+++ b/include/deal.II/lac/sparse_direct.h
@@ -304,9 +304,12 @@ public:
         "want to check your assembly procedure. Similarly, a "
         "matrix can be rank deficient if you forgot to apply the "
         "appropriate boundary conditions. For example, the "
-        "Laplace equation without boundary conditions has a "
-        "single zero eigenvalue and its rank is therefore "
-        "deficient by one."
+        "Laplace equation for a problem where only Neumann boundary "
+        "conditions are posed (or where you forget to apply Dirichlet "
+        "boundary conditions) has exactly one eigenvalue equal to zero "
+        "and its rank is therefore deficient by one. Finally, the matrix "
+        "may be rank deficient because you are using a quadrature "
+        "formula with too few quadrature points."
         "\n\n"
         "The other common situation is that you run out of memory. "
         "On a typical laptop or desktop, it should easily be possible "