dolfin team mailing list archive

[Johan Jansson <jjan@xxxxxxxxxx>]

Hi!

Me and Peter Brune ran into an issue with coefficient initialization for 
functionals, specifically that the mesh is missing.

In the lift-drag demo in DOLFIN you have:

Function p(Vp, "../pressure.xml.gz");
FacetNormal n;


If you do:

Lift::Functional L(p, n);

then this works fine.

And that is equivalent to doing:

Lift::Functional L;
L.p = p;
L.n = n;

which also works fine.

However, if you switch the order:

Lift::Functional L;
L.n = n;
L.p = p;

then you get a dolfin_error with:

 what():  *** Error: Unable to extract mesh from form (no mesh found).

from:

Lift::Form_0_Coefficient_n::create_function_space

(it's trying to do something like this: new 
Form_0_FunctionSpace_0(form.mesh()); without the form having a mesh)

We suggest to solve this by requiring a mesh argument for Functional 
initialization. What do you think?

For now we've solved this by re-ordering the arguments to our functional 
(to give the coefficient with a function space as the first argument), 
but you could have cases where none of the coefficients have a function 
space at the time of the functional initialization.

 Johan