dolfin team mailing list archive

["Martin Sandve Alnæs" <martinal@xxxxxxxxx>]

2008/12/2 Anders Logg <logg@xxxxxxxxx>:
> Would it be difficult to add the possibility of sending in a SymPy or
> Swiginac expression to the Function constructor? As I understand, both
> can generate C++ code so it seems we could reuse what we already have
> for cppexpr.

Trivial. Except that the symbols used must be named like
x = swiginac.symbol("x[0]") etc from the user side, we can
just call "swiginac_expression.printc()" to get a scalar string.
Eventually "swiginac_expression.evalm().evalf().printc()"
to be on the safe side.

> Then, one could do things like
>
> f = Function(V, sin(x))
>
> which would be close to optimal.

You're forgetting namespace clashes here...
In real code there will have to be detailed imports from different
modules or explicit namespace handling to separate
sympy.sin, numpy.sin, ufl.sin and math.sin.

> The best of course would be if one
> did not need to first define f and then use it, but instead could
> write it directly in the form:
>
> L = v*sin(x)*dx

We can do that easily if we add terminal symbols x,y,z or x[0], x[1],
... to UFL.

from ufl import *
polygon = triangle
element = FiniteElement("CG", polygon, 1)
v = TestFunction(element)
x = SpatialCoordinate(polygon)
f = sin(x[0])
a = f*v*dx

Generated quadrature code can handle this directly, while tensor
representation would require some function extraction magic.

--
Martin