From j.edelmann at stud.uni-heidelberg.de  Mon Mar 11 13:29:34 2024
From: j.edelmann at stud.uni-heidelberg.de (Joris Edelmann)
Date: Mon, 11 Mar 2024 13:29:34 +0100
Subject: [dune-pdelab] Error in PDELab
Message-ID: <ca8ef542-3b78-a868-0fda-dfe2aae27c97@stud.uni-heidelberg.de>

Hi,

I recognized, that in 
dune-pdelab/dune/pdelab/gridfunctionspace/gridfunctionspaceutilities.hh 
is an error:

In the class  VectorDiscreteGridFunctionGradient  and therein in the 
method "evaluate" is a miscalculation. The gradient is transformed via a 
multiplication with

JgeoIT = e.geometry().jacobianInverseTransposed(x);

It should be

JgeoIT = e.geometry().jacobianTransposed(x);

In the latter case, the derivative coincides with the one calculated via 
Paraview. Mathematical argument:

map mu: local to global,

Funktion: local to R^n: f(mu(x))

Gradient: grad(mu)^T grad(f)(mu(x)) (chain rule)


I'm using the dune verion 2.8


Best,

Joris