From: Wolfgang Bangerth <bangerth@colostate.edu>
Date: Mon, 6 Jan 2020 19:48:49 +0000 (-0700)
Subject: Augment the UMFPACK error message.
X-Git-Tag: v9.2.0-rc1~722^2
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=refs%2Fpull%2F9235%2Fhead;p=dealii.git

Augment the UMFPACK error message.
---

diff --git a/include/deal.II/lac/sparse_direct.h b/include/deal.II/lac/sparse_direct.h
index a354636531..ee20a40124 100644
--- 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 "