Subject: [FFC-dev] DG method for elasticity

From: Brandon Chabaud <[email-masked]>
Date: Mon, 16 Feb 2009 17:47:28 -0600

Hello,

Here is the problem that I'm having.  I want to implement a discontinuous
Galerkin method for a 2D elasticity problem.  The boundary is divided into
two subsets: Gamma_0 and Gamma_1.  One of my unknowns is the vector u, the
displacement.  Boundary conditions are imposed weakly.  In my formulation of
the method, I have a term of the form

<u_i*n_j,v_i*n_j>_{Gamma_0},

where n is the facet normal and < , >_{Gamma_0} means the integral over
Gamma_0.  Using the built-in exterior facet integral measure *ds in my .form
file will cause the compiler to integrate the term over both Gamma_1 and
Gamma_0.  How do I restrict the integration to Gamma_0 only?  Thanks.

Brandon Chabaud

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From: Anders Logg <[email-masked]>
Date: Tue, 17 Feb 2009 07:21:27 +0100

On Mon, Feb 16, 2009 at 05:47:28PM -0600, Brandon Chabaud wrote:
> Galerkin method for a 2D elasticity problem.  The boundary is divided into two
> subsets: Gamma_0 and Gamma_1.  One of my unknowns is the vector u, the

Use ds(0), ds(1) etc to specify integration over sub sets of the
boundary. Then you need matching mesh markers (MeshFunction over the
facets) to indicate the different sub sets when assembling.

-- 
Anders