dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Fri, Feb 11, 2011 at 08:08:32AM -0800, Johan Hake wrote:
> On Friday February 11 2011 01:16:31 Anders Logg wrote:
> > How is DOLFIN_EPS treated in Expressions and boundary conditions
> > (using compile_subdomains)?
> >
> > I thought that DOLFIN_EPS was known to the JIT compiler.
> >
> > Here are somethings I noted while debugging a code:
> >
> > 1. f = Expression("sin(x[0] + DOLFIN_EPS)") does not compile.
> >
> > The log file pointed to by the JIT compiler says "syntax error" and the
> > generated code in .i file found in the same directory contains this:
> >
> > class Expression_5d66d4e2b02f54f6088fc61767e40073: public Expression
> > {
> > public:
> >   double DOLFIN_EPS;
> >   Expression_5d66d4e2b02f54f6088fc61767e40073():Expression()
> >   {
> >
> >     DOLFIN_EPS = 0.0;
> >   }
> >
> >   void eval(dolfin::Array<double>& values, const
> >   dolfin::Array<double>& x) const
> >   {
> >     values[0] = sin(x[0] + DOLFIN_EPS);
> >   }
> > };
> >
> > So there are two problems here:
> >
> > 1.a) The JIT compiler fails to compile the Expression f which looks
> > like a valid expression to me
> >
> > 1.b) DOLFIN_EPS is set to zero.
>
> Now it doesn't.

Thanks!

> > 2. When trying something similar with compile_subdomains, it seems
> > that
> >
> >   compile_subdomains("x[0] < DOLFIN_EPS")
> >
> > compiles and produces correct code. In particular the .i file does not
> > contain DOLFIN_EPS = 0.0.
>
> subdomain treats DOLFIN_EPS and on_boundary seperately.
>
> > But the magic for creating variables is a bit too clever. I had a typo
> > which said "DOFLIN_EPS" instead of "DOLFIN_EPS" which compiles without
> > any warnings and DOFLIN_EPS is set to zero. That's a litle dangerous.
>
> You cannot blame your typos on compile expressions ;)

I just did! ;-)

Would it be possible (and desirable) to require default values for all
variables in an Expression?

f = Expression("a*x[0]", a=2.0)
f.a = 3.0

The current implementation is impressively clever to figure out variable
names automatically, but it also means that all variable names that
are misspelled are automatically set to zero without warning.

--
Anders