This simple test program demonstrates how to implement a PDE solver
with DOLFIN.

The problem first needs to be stated in variational form: Find u in V
such that

    a(v, u) = L(v)    for all v in V.

DOLFIN uses the FEniCS Form Compiler FFC to process variational forms.
The bilinear form a and the linear for L are here specified in the file
Poisson.form which can be compiled using the command

    ffc Poisson.form

to create the file Poisson.h included in the main program.

The simple test program saves the solution in DOLFIN XML format to the
file poisson.xml, which can be visualized using the script plot.py:

    python plot.py

This script assumes that you have PyDOLFIN installed. Since PyDOLFIN
depends on Viper for plotting, you also need to have Viper installed.
