# [Gmsh] Boundary Conditions.

Stott CH Mr (PG/R - Maths & Statistics) C.Stott at surrey.ac.uk
Tue Oct 19 15:12:14 CEST 2004

```Hi,

I've searched through the manuals and the mailing list archives, but can't find an answer to this.

Say I define a square domain...

lc=0.1;

Point(1) = {0, 0, 0, 0.1*lc}; Point(2) = {1, 0, 0, lc}; Point(3) = {0, 1, 0, lc}; Point(4) = {1, 1, 0, lc};
Line(1) = {1,2}; Line(2) = {2,4}; Line(3) = {4,3}; Line(4) = {3,1};

Line Loop(5) = {1,2,3,4};
Plane Surface(6) = {5};

I want to use this with a diffusion solver, with two types of boundary conditions (Dirichlet and Neumann). So I set up some Physical Entities,

Physical Line(10) = {1,2,3};
Physical Line(11) = {4};

Physical Surface(100) = {6};

Say I want to have a zero Neumann condition on Physical Line 10, and a non-zero Dirichlet condition on Physical Line 11. Do I have to hard code the numerical values of these into my solver? or is there someway of attaching extra data to a Physical Line?

I could do something like,

Physical Line(0.0) = {1,2,3};
Physical Line(2.5) = {4};

but then how would I specify which condition was which?

Also, is it possible in gmsh to have more involved conditions (non-constant values across a line, Gaussian blob initial conditions, etc)?

Many thanks,

Chris Stott

Department of Mathematics
University of Surrey
United Kingdom
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