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fem-fenics questions


From: Daniel Kraft
Subject: fem-fenics questions
Date: Mon, 03 Mar 2014 09:53:07 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.3.0

Hi!

I've recently started playing around with fem-fenics, and it works very
well for my application so far.  Here are just some questions I came
across and wanted to discuss:

1) Whenever I run my script using fem-fenics (presumably during the call
to import_ufl_Problem), I see a cc1plus process popping up and using 10
s or so finish.  (This can also be seen with the Poisson example.)  I
understand that this is necessary to compile my UFL form.  Is it
possible to somehow skip this step unless the UFL file was changed?  It
takes a not negligible amount of processing time for my code and I don't
think the UFL file will change often.

2) Since I do not only want to plot the result but also work with it
further, I need to evaluate the result at my grid points.  With linear
Lagrange elements, I "could" use the coefficients obtained directly, but
this is probably a bad idea from the point of view of code design.  Thus
I'm using feval now, but it is not entirely clear to me how it is
supposed to be called.  The doc only says the second argument should be
the "coordinate" of evaluation, but doesn't specify how this coordinate
should look like.  It works for me now if I pass an array of x- and
y-coordinate.  I guess this is how the function is meant to be called?
Is it also possible to invoke it for lots of points at all?  (I think I
read somewhere that this is planned but not yet implemented ... just
checking what the current state is.)  This is a very important feature,
IMHO, for everyone working seriously with the result afterwards (and not
just plotting it).

3) I use different directories for components of my code, and use
addpath to access them.  The code invoking fem-fenics and my UFL file
are in one of those directories (say, A/), but when I try to use it from
a different one (B/), fem-fenics tries to access my UFL file in B/.
I've created a symlink B/problem.ufl -> A/problem.ufl for now, but I
think that UFL files should be read relative to the script using
import_ufl_*.  Or is it designed the way it is for some reason?

Thanks for the great work, I'm just starting to enjoy what you can do
with fem-fenics and it looks very good so far (for my own research's
requirements at least).

Yours,
Daniel

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