From 4a2835636b1c670b557d13fd1af6e899b31a3441 Mon Sep 17 00:00:00 2001 From: Wolfgang Bangerth Date: Thu, 23 Jan 2020 10:11:55 -0700 Subject: [PATCH] Improve an error message. --- include/deal.II/numerics/derivative_approximation.h | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/include/deal.II/numerics/derivative_approximation.h b/include/deal.II/numerics/derivative_approximation.h index be3854dd8c..bbe1450348 100644 --- a/include/deal.II/numerics/derivative_approximation.h +++ b/include/deal.II/numerics/derivative_approximation.h @@ -307,11 +307,16 @@ namespace DerivativeApproximation * Exception */ DeclExceptionMsg(ExcInsufficientDirections, - "We have encountered a cell on which the number of linearly " + "While computing a finite difference approximation to " + "derivatives, the algorithm encountered a cell on which " + "the number of linearly " "independent directions that span the matrix Y (discussed " "in the documentation of the DerivativeApproximation " "class) is not equal to dim. The matrix Y then is " - "rank deficient and can not be inverted."); + "rank deficient and can not be inverted. A common reason " + "why this might be happening is if a cell has neither " + "left/right (or up/down, or front/back) neighbors, for " + "example because the mesh is too coarse."); } // namespace DerivativeApproximation -- 2.39.5