The gyromidpoint of a gyrosegment.
gyromidpoint(A, B, s = 1, model = "U")A point, the gyromidpoint of a the gyrosegment
joining A and B.
two distinct points (of the same dimension)
positive number, the radius of the Poincaré ball if
model="M", otherwise, if model="U", this number
defines the hyperbolic curvature
the hyperbolic model, either "M" (Möbius model, i.e.
Poincaré model) or "U" (Ungar model, i.e. hyperboloid model)