Because a Stiffness does provide a first derivative.

Currently, all implementations of variational problems inherit
from LocalGeodesicFEStiffness, which requires gradient and Hessian
implementations.  However, most of these implementations really
only implement the energy, and leave computations of first and
second derivatives to algorithmic differentiation.  To make
this clearer, this patch introduces an abstract base class
LocalEnergy for all implementations that really only have
an energy.

This is how the new dune-functions bases should be used.  Also, it is yet
another step towards merging CosseratEnergyLocalStiffness and MixedCosseratEnergy.

[[Imported from SVN: r10112]]

Conceptually cleaner, and makes for simpler code.  Most importantly, we will want
to pass the Basis::LocalView to the local assemblers.  For that we need the actual
basis, not just the grid view and local finite element.

[[Imported from SVN: r10082]]

Instead, the FD approximation is now done in a separate class.

[[Imported from SVN: r9850]]

Because the gradient is needed anyway when computing the Hesse matrix.
Not computing it separately a second time shaves off about 8% wall time
of each iteration.

[[Imported from SVN: r9555]]

ADOL-C doesn't play nice with OpenMP.  Hence we have to disable
the latter for the time being.

[[Imported from SVN: r9446]]

[[Imported from SVN: r9421]]

[[Imported from SVN: r9391]]

[[Imported from SVN: r9390]]

[[Imported from SVN: r9294]]

[[Imported from SVN: r9284]]

the ones with i<=j.  The rest follows from symmetry of
the Hessian.

Needless to say, this makes the Hessian assembly quite
a bit faster.

[[Imported from SVN: r8587]]

The speed increase cause by the patch is, alas, hardly measurable.

[[Imported from SVN: r8360]]

[[Imported from SVN: r7837]]

[[Imported from SVN: r7611]]

and barycentric coordinates.  This is easy because we know the
number of element corners at compile time (I currently don't
see support for non-simplex elements at all).  This saves 
time, but not much: about 1%.

[[Imported from SVN: r7550]]

[[Imported from SVN: r7426]]

[[Imported from SVN: r7424]]

remove projection onto tangent space.  Is the variations are all tangent to the manifold you don't actually need it

[[Imported from SVN: r7422]]

[[Imported from SVN: r7391]]

[[Imported from SVN: r7390]]

Be smarter about when to compute what.  This speeds up assembly of the Hessian for harmonic maps from R^3 to S^2 by a factor of 3

[[Imported from SVN: r7389]]

[[Imported from SVN: r7388]]

Remove class specializations.  The old implementation for the UnitVector class will handle all cases

[[Imported from SVN: r7380]]

[[Imported from SVN: r7379]]

[[Imported from SVN: r7378]]

[[Imported from SVN: r7374]]

Remove a few specializations.  From now on we will assume that all target spaces can be parametrized by some sort of global embedding.  I don't see a case coming where that is not general enough

[[Imported from SVN: r7373]]

[[Imported from SVN: r7338]]

[[Imported from SVN: r7312]]

[[Imported from SVN: r7176]]

[[Imported from SVN: r7174]]

[[Imported from SVN: r7089]]

[[Imported from SVN: r6718]]

[[Imported from SVN: r6499]]