FUNCTION:  CharPoly - characteristic polynomial of a group element,    
CALLING SEQUENCE:  CharPoly(w,R); ,                   CharPoly(w,R,t);
    ,PARAMETERS:  R = a root system data Structure
             w = a list of integers representing a member of W(R)
             t = a variable or expression (optional),SYNOPSIS:   
  If R is a root system of Rank n, members of the Coxeter group W(R) are
  represented as lists of integers in the range 1..n. The group element
  corresponding to w = [i_1,...,i_l] is the product of the generators
  Indexed by i_1,...,i_l. The Indexing follows Base(R).
  If w is such a group element, CharPoly(w,R,t) computes the determinant
  of 1 - t*w, as a linear transformation of the space spanned by Base(R).
  If the third argument is omitted, q is the default.
  For a description of root system data Structures, see Coxeter[Structure].
EXAMPLES:   
  CharPoly([1,3,2,3],B3);        yields           1-q+q^2-q^3
  CharPoly([1,2,3,4],D4,1);      yields                4
  CharPoly([1,2,3,2],H3,z);
  evalf(",3);                     yields   1.-1.62*z+1.62*z^2-1.00*z^3,    
