make triangulation tests stronger with more randomness
Currently we test against the standard simplex.
We could improve matters by applying a random affine transform to the standard simplex, and checking that the tests still pass.
We would also need to have functions for generating points around simplices (inside, outside, on face). This should not be too hard.
For example we can generate points on a face by choosing ndim
positive random numbers from successively smaller intervals, and then choosing a final number so that the sum is 1. These are the coordinates of a point in a simplex in the basis of the vertex vectors.