dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Wed, Jun 04, 2008 at 12:44:17PM +0200, Martin Sandve Alnæs wrote:
> 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!

Very nice! I haven't tried it until now but it seems to work.

I copied your email into the manual. Until we have worked up the
motivation to start taking care of the manual (which we need to do in
a not so distant future), let's add tutorials/instructions from the
mailing list into the manual for later editing. It's good to add it
while it's fresh and the author still remembers what he was
thinking. :-)

-- 
Anders

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