From 842b40785c7e822959826a449f5cd0eb11559b26 Mon Sep 17 00:00:00 2001 From: Wolfgang Bangerth Date: Mon, 6 Jan 2020 12:48:49 -0700 Subject: [PATCH] Augment the UMFPACK error message. --- include/deal.II/lac/sparse_direct.h | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) 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 " -- 2.39.5