FUNCTION:  Orbit_Size - Size of a Reflection group Orbit,    
CALLING SEQUENCE:  Orbit_Size(v,R);,                   Orbit_Size(v,R,-1);
    ,PARAMETERS:  R = a root system data Structure
             v = a linear combination of e1,e2,...,SYNOPSIS:   
  A "vector" (distinct from the vector data Structure used by Maple) is a
  linear combination of the standard orthonormal basis e1,e2,e3,..., with
  coefficients that are rational or floating-point.
  If v is a vector, Orbit_Size(v,S) returns the Size of the Orbit of W(R)
  acting on v by Reflections. This number is determined by finding a set
  of Reflections that generate the stabilizer of v. If any floating-point
  coordinates occur in v or Base(R), then there is a (small) potential for
  error, in that the Reflection corresponding to a root r is considered to
  fix v if abs(Iprod(r,v)) is at most epsilon ( = 0.001, by default).
  If a third argument is present, the number returned is the Size of the
  union of the Orbits of v and -v, or equivalently the Size of the Orbit
  of v under the action of the group generated by -1 and W(R).
  To adjust epsilon, assign a new value to Coxeter/default[epsilon].

  For a description of root system data Structures, see Coxeter[Structure].
EXAMPLES:   ,  with(Weyl,Weights); w:=Weights(D5);
  Orbit_Size(w[1],D5);                        yields      16
  Orbit_Size(w[1],D5,-1);                     yields      32
  v:=Base(H4)[1];
  Orbit_Size(v,H4);                           yields      120,    
SEE ALSO:  Base, Iprod, Orbit, Size, Structure, Vec2FC):
