Cell index in facet integral

[c_cosm]

Hello,

I’m looking for a way to get an index to the cell that a facet belongs to during integration over said facet, which I can then use to find that cell’s physical region given by a MeshFunction.

I have two subregions in my mesh with a different constant on each of them and I need to use the appropriate value during integration over the facets along their interface (something like my_constant(’-’)).

Is there a way to do this?

Thank you

[kamensky]

See @MiroK’s answer here:

Integrating over an interior surface

Hi, consider using restriction using + and -. Here foo('+') restricts foo to the positive cell and FacetNormal('+') is the outer normal of a positive cell. Following the discussion here the +, - side can be changed by providing a form which has a dx measure term which has specified subdomain_data by some cell function g. Then a positive cell for a facet is the one for which value of g is higher. This allows for the following from dolfin import * from mshr import * omega1 = Rectangle(Point(0, 0…

You can use the MeshFunction to control which subregion is the - side of an interior facet, which should allow you to do what it sounds like you’re trying to.