dolfin team mailing list archive

["Garth N. Wells" <g.n.wells@xxxxxxxxxx>]

On Mon, 2006-02-13 at 17:06 +0100, Johan Jansson wrote:
> On Mon, Feb 13, 2006 at 09:39:14AM -0600, Anders Logg wrote:
> > On Mon, Feb 13, 2006 at 02:46:04PM +0100, Johan Jansson wrote:
> > 
> > > I think two remaining features to implement are:
> > > 
> > > 1. Loading Functions (DiscreteFunction) from file.
> > 
> > ok, which format do we want to do initially? DOLFIN XML?
> > 
> > Maybe we should also consider some binary format that is quicker to
> > write and parse? Could be useful mostly during computations (and less
> > useful for storing solutions for future reference) for example when
> > solving the dual problem and linearizing around a previously computed
> > solution (or time sequence of solutions) that doesn't fit in memory.
> 

I think that an XML format would be great. Considering problems which
won't fit into the memory is still some time away. I'd lile to be able
to write functions to a file to allow restarts. 


> Isn't a natural candidate the VTK format? This is the standard output
> format for DOLFIN, isn't it natural to be able to read it back in?
> 

VTK is limited in the types of elements on which the functions are
defined (linear and quadratic, although the output for quadratic
elements looks weird because ParaView doesn't draw the element, but
makes it's own triangulation of the surface based on the provided data),
so values away from vertexes would be lost, and it doesn't handle
discontinuous functions.

> > > 2. An interface for projecting/interpolating between Functions. The
> > > main example which requires some manual work in solvers is defining
> > > the initial values by a UserFunction and wanting to represent that as
> > > a DiscreteFunction.
> > 
> > I'm not sure what you mean. I thought I solved this with the new
> > functionality I added to the Function class last week. You can define
> > a Function for the initial value by overloading eval(), or even by
> > 
> > Function u = 0.0;
> > 
> > and then u can change from being a user-defined Function to a discrete
> > Function. See new convection-diffusion demo.
> > 
> > You can also do
> > 
> > Function u(x, mesh, element);
> > u = f;
> > 
> > to interpolate f to u.
> > 
> 
Is the interpolation linear (to the vertexes only), or does it work for
higher-order elements?

Garth

> Ok, great! I'm sorry, I didn't realize this was what you added last
> week.
> 
> I think interpolation is enough, projection can wait.
> 
> > I have limited time to work on new features before Geilo, but I can
> > probably fit something in if I get some help.
> > 
> 
> Yes, I also have limited time. But maybe we can at least start looking
> at Function input and decide what we should do, i.e. if we should
> design a DOLFIN XML data format for Functions or use the VTK format.
> 
>   Johan
> 
> _______________________________________________
> DOLFIN-dev mailing list
> DOLFIN-dev@xxxxxxxxxx
> http://www.fenics.org/cgi-bin/mailman/listinfo/dolfin-dev
-- 
Dr. Garth N. Wells
Faculty of Civil Engineering and Geosciences
Delft University of Technology
Stevinweg 1
2628 CN Delft
The Netherlands

tel.     +31 15 278 7922
fax.     +31 15 278 6383
e-mail   g.n.wells@xxxxxxxxxx
url      http://www.mechanics.citg.tudelft.nl/~garth