FUNCTION:  WeightCoords - coords of a vector w.r.t. fundamental Weights
    ,CALLING SEQUENCE:  WeightCoords(v,R);,    
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 in the span of Base(R), WeightCoords(v,R) returns the
  list of coordinates of v relative to the fundamental Weights (Weights(R)).

  More generally, v can be any linear combination of e1,e2,..., provided
  that the function calls coeff(v,e1),coeff(v,e2),... return valid answers.
  That is, the coefficients of v need not be rational or floating-point.

  For a description of root system data Structures, see Coxeter[Structure].
EXAMPLES:   
  WeightCoords(Rho(F4),F4);            yields        [1,1,1,1]
  WeightCoords(a*e1+b*e2+c*e3,B3);     yields    [2*a, -a+b, -b+c],    
SEE ALSO:  Weights, Coxeter[RootCoords], Coxeter[Structure]):
