dolfin team mailing list archive

[Bartosz Sawicki <sawickib@xxxxxxxxxxxxx>]

phil marinier wrote:
> sry about the subject line.
>
> I understand how to use grad() in my .ufl file that I then compile to
> get a .h file. What I don't understand is how to use grad() inside my
> actual code.

In .ufl file you describe forms, then it is compiled to .h, then in C++ 
you define VariationalProblem using forms from .h, and finally you have 
to solve it.

Fenics is all about linear forms. You need to understand this concept to 
use this software efficiently.


> I am iterating my boundary condition depending on the gradient normal
> to the surface. To do this, I need to be able to find the gradient
> from inside my program. Maybe I'm just missing something, but the way
> I understand it is that I cannot use grad() directly in my C++
> program, only in my .ufl file, but if I were to use python, I would
> be able to use grad() directly in my program. I am unable to test
> this out due to unrelated problems with my compiler that I'm slowly
> working through.

In python you have just simple interface to create forms, but it doesn't 
mean that you can directly calculate gradient without solving 
variational problem.

> What I want to end up with is a C++ function that takes in a dolfin
> Function and outputs a C++ vector of the gradients normal to the
> boundary at each node.

I'm not sure how to describe your problem in UFL language. Definition of 
vector normal to the boundary at vertex will be troublesome.

cheers,
BArtek


> Thanks for your help
>
> Phil
>
>
>
>
>
> > Date: Wed, 8 Jul 2009 14:25:23 -0600 From: sawickib@xxxxxxxxxxxxx 
> > To: lonewolf_13p@xxxxxxxxxxx CC: dolfin-dev@xxxxxxxxxx Subject: Re:
> > [DOLFIN-dev] (no subject)
> >
> > Phil, could you please give subject to your emails. Subject is very
> >  important part of a message, it help readers to classify it.
> >
> > Python dolfin module is just an interface to the C++ library, so
> > every functionality available in python is in C++ too. Remember
> > that to use grad() in C++ you need to define UFL form.
> >
> > cheers,

> > phil marinier wrote:
> > > I need to find the gradient perpendicular to the boundary. I know
> > > I can find the gradient in python using the grad(v) command, but
> > > I don't think I can do the same in C++. Is it possible? and if it
> > > is possible is it worth the trouble or would it be easier to
> > > rewrite in python? Thanks for your help
> > >
> > >
> > >
> > > ------------------------------------------------------------------------
> > >
> > >
> > >
> > > _______________________________________________ DOLFIN-dev
> > > mailing list DOLFIN-dev@xxxxxxxxxx 
> > > http://www.fenics.org/mailman/listinfo/dolfin-dev