The driver solves the PDE given by the first form in forms. This is a
first step towards instationary problems.

It allows the sorting of preambles having different
cache item type.

Feature matrix free solution of linear PDEs

This implements matrix free solution of linear PDEs. Some notes:

1. Right now the code simply uses BiCGSTAB from istl from istl for solving the linear systems. A more subtle solver setup should be postponed until the istl-ini factory arrived at PDELab.
1. Poisson DG doesn't converge. Tests with the convectiondiffusiondg lop from PDELab show that the hand written lop has the same behaviour. Because of that I turned off DG tests.
1. Right now nonlinear PDE's are not covered since PDELab doesn't seem to support nonlinear matrix free solutions. We probably have to adjust Newton first.

This merge request is related to #26 and I will update the issue accordingly.



See merge request !10

Tests/poisson variations

Test various poisson variations:

- 1D/2D/3D
- CG/DG
- triangles/quadrilaterals

This closes #19 and #18.

See merge request !9

Revert "Use loopy for evaluation of basis gradient"

This reverts commit d0a87348.

See merge request !8

This reverts commit d0a87348.

Feature/exact solution from ufl

Adds three form compiler arguments that:

- Tell the form compiler which expression of the ufl file represents the exact solution.
- Enable comparison dof vectors of numerical solution and interpolation of exact solution.
- Enable calculation of l2errorsquared of difference between numerical solution and interpolation of exact solution.

These methods only work for scalar equations. For Mixed-/Vector-/Tensorelements an exception is raised.



See merge request !7

NOTE: Works only for scalar equations

Export data object instead of namedata object



See merge request !6

Compare DBC to numerical solution

Makes it possible to compare numerical solution and dirichlet boundary condition by setting the formcompiler option '--dirichlet-is-exact-solution'.

Comparing means finding the maximum error in the dof vectors and throwing an error if it is too large. If you have any suggestions for better comparisons or option/functions names just let me know. 

See merge request !5

Solve nonlinear problem

Make it possible to solve simple nonlinear problems.

It would be nice to have a DG test case but we don't have a lop for creating a reference solution. I will open an issue for that and remove WIP from this merge request.

See merge request !4

Merge branch 'feature/nonlinear' of http://conan2.iwr.uni-heidelberg.de/git/dominic/dune-perftool into feature/nonlinear

Merge branch 'feature/nonlinear' of http://conan2.iwr.uni-heidelberg.de/git/dominic/dune-perftool into feature/nonlinear

Use loopy for evaluation of basis gradient

Implements #17

See merge request !2

Add include to vtkpredicate

Needed  to build all the tests.

See merge request !1