dolfin team mailing list archive

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

2008/6/3 Anders Logg <logg@xxxxxxxxx>:
> On Tue, Jun 03, 2008 at 11:23:41PM +0200, Martin Sandve Alnæs wrote:
>> It's easy with some helper functions I have, I can show you tomorrow.
>> It only depends on dolfin::Function (i.e. dolfin.cpp_Function) and Instant.
>
> ok, nice. Maybe we can add the helper functions to assemble.py.

Now you can do things like this:

A = assemble(..., coefficients=[myfunction, 1.23, "sin(x[0])"])

1.23 is wrapped in a cpp_Function (i.e. a constant Function), and
the string is compiled as a C++ dolfin::Function like "v[0] = ...;".

If you want more control over the implementation
(i.e. temporary variables in eval for efficiency, if-checks, etc.)
you can also do this:

code = """
class F: dolfin::Function {
 ...
};
class G: dolfin::Function {
 ...
};
"""

f, g = compile_functions(code, mesh)


Or, if you just want to precompile but don't need anything too fancy:

expressions = ["sin(x[0])",
                         ("a*x[1]", "b*x[0]")]
f, g = compile_functions(expressions, mesh)
assert f.rank() == 0
assert g.rank() == 1
g.a = 1.23
g.b = 3.21

Note that:
- a tuple is interpreted as a vector expression

- a tuple of tuples is interpreted as a matrix expression

- variables like a and b in the strings above are detected
  automatically, but this requires all builtin names to be
  registered in the variable dolfin.compile_functions._builtins,
  which currently contains some common mathematical
  functions like sqrt, pow, exp, sin, pi etc.

- variables are initialized to 0.0, so use compile_functions if
  you need control over variable values.

- assemble also accepts tuples like in compile_functions

- assemble only calls on instant once independently of
  the number of string expressions, to reduce compilation time

- Error checks are not extensive!

--
Martin