Make them a parameter instead.  This allows to switch more easily between
geodesic finite elements and projected finite elements.

Make them a parameter instead.  This allows to switch more easily between
geodesic finite elements and projected finite elements.

It still tested for the dune-fufem wrapper of a first-order basis, while nowadays
the RiemannianTRSolver class is instantiated with dune-functions bases.

It is still no function in the dune-functions sense, but at least the
basis parameter needs to be a dune-functions basis now, rather than
a deprecated dune-fufem basis.

This is needed to be able to multiply FieldMatrices with Quaternions.

Needed for gradient-flow applications.

According to Hanne, this is needed to turn 1d harmonic map heat flow into true
curve-shortening flow.

Hardwiring the weighting here is very hacky.  Something more flexible and
general will need to be implemented eventually.

Apparently, nobody had used the evaluateDerivativeLocal method before.

This are needed by the gradientflow code to implement the implicit Euler method
for an L2 gradient flow.

This is an initial version; it currently only works for a very limited set of
cases.  I tested it for triangle grids, and that works.

This is needed for the new gradientflow application.  The standard 'distance' method
doesn't cut it, because it is not differentiable near zero.  Therefore, even the
differentiable expression 'distance*distance' will fail to be differentiable for
an automatic-differentiation system.  I think in the long run we should replace
'distance' by 'distanceSquared' everywhere it is used.

Unfortunately, this patch is hacky: it only adds the method for the double/adouble
combination.

Previously, the NonplanarCosseratShellEnergy had the normal field of the unit sphere
hard-wired in the code.  With this patch, using general triangulated surface as
reference geometries is possible.

For some reason clang doesn't like it, and we are not using OpenMP anyway.

I want this file with dimworld!=3 grids, even though it only makes sense
to use it if dimworld==3.

With this patch the file still does not compile.  However, the only remaining
problem is the hacky computation of the surface normals, which needs to be
rewritten in full generality soon anyway.

We can now completely control the approximation order by a const int,
which is much nicer.

The method using the SVD works in principle.  However, it does not play nicely
with automatic differentiation, because singular values are not always differentiable.

The method proposed by Higham to compute the polar factor, on the other hand,
is a Newton method at heart.  Therefore, it can be used together with AD without
problems.

They only make sense if the 'adouble' type is known.

I intend to move as much towards the dune-functions interface for functions,
and this is a first step.

Introduce preprocessor variable PROJECTED_INTERPOLATION to switch between geodesic FE and projection-based FE

This is a temporary solution; we need something smarter eventually.

Rationale
a) Code is much simpler without it
b) Code compiles faster without it
c) P3 functions are now downsampled to P2 functions, rather than to P1 functions.
   Hence there is less loss of information now.

Simply ask the first local finite element of the dune-functions basis for the order.