function cn=coeff(fcns,efcns,wn,x)
 
  $Id: coeff.m,v 1.19.1.6 2003-06-22 01:02:05-05 brinkman Exp $
  (c) 2002, Peter Brinkmann (brinkman@math.uiuc.edu)
 
  coeff: computes coefficients of series expansions with respect to
 	some system of orthogonal functions
 
  Usage: cn=coeff(inline('sign(x)','x'),'sinef',(1:5)'*pi,linspace(-1,1,100));
 
  Parameters:
    fcns: inline function of one variable to be developed into a series,
 		or a string containing the name of the function to be used
 		(see .octaverc for the implementation of inline functions under
 		Octave)
    efncs: a function that computes some system of orthogonal eigenfunctions,
 		given by a string containing the name or by an inline function
 		Note that these eigenfunctions do not need to be normalized because
 		coeff.m takes care of normalization.
    wn: column vector of square roots of eigenvalues
    x: row vector of x-values
 
  Return values:
    cn: column vector of coefficients of fcns with respect to the system
 		given by efcns and wn, computed with the trapezoidal rule
 
  The usage example computes the first five terms of the Fourier sine
  series of the function sign(x) on the interval [-1,1]. The function
  passed in the parameter efcns must conform to a certain interface that
  is described in the file cosef.m. Examples of functions conforming
  to the interface include cosef.m and sinef.m.
 
  The coefficients cn are approximated using the trapezoidal rule. The
  vector x indicates where the function fcns will be evaluated. It
  does not have to be evenly spaced. In general, the quality of the
  approximation will depend upon the number of points in x.