
example_alpha : read input points, compute the alpha shape in 
regularized mode and find the optimal value of $\alpha$, i. e. the smallest
$\alpha$ such that all input point are interior or on the boundary of the
alpha shape and the alpha shape has a single connected component.

example_big_alpha : buid the alpha shape for a huge set of points using
a Delaunay hirarchy as underlying triangulation for efficiency.

example_weight : build the weighted alpha shape of a small
set of spheres  and explore the  boundary of the alpha complex for $\alpha =0$.
This complex is the nerve of the union of the spheres.
