Neumann condition

General Discussion
1

Hello everyone.
how to calculate the outward normal vector.
Because I want to find the value of Neumann condition.

When I use :
Neumann= dx(Uex)*N.x+dy(Uex)*N.y

I found
Neumann=
000000
000000
…
NB: Uex is the exact solution
Thanks.

2

The problem is by default N.X and N.Y is not defined correctly in general.

3

Merci cher professeur Frédéric pour votre réponse
Donc il n’existe pas un macro qui permet de calculer la condition de Neumann.
Cordialement.

4

You can lnear form to evaluate Neuman Condition on Poisson equation.



varf vNeuman(used,v) = int1d(Th)(v*(dx(Uex)*N.x+dy(Uex)*N.y)/lenEdge);
Vh vn; // Finite element function to store the Normal derivative
vn[]= vNeuman(0,Vh);

plot(vn,wait=1);