HELP FOR PROGRAM NLINSYST

  
  This program solves a nonlinear system of two variables:

       f(x,y) = 0
       g(x,y) = 0

  We use here a generalized Newton's method called linearization
  method.

  Starting from an initial point, (x0,y0), two series, Xn and Yn,
  are built, converging towards the system solution, alpha, beta.

  The series are defined by:

                    fg'y - gf'y
       Xk+1 = Xk - -------------
	              delta

                    gf'x - fg'x
       Yk+1 = Yk - -------------
                      delta

  with  delta = f'x.g'y - f'y.g'x
  
  f'x = partial derivative of f with respect to x
  f'y = partial derivative of f with respect to y  	   
  g'x = partial derivative of g with respect to x       
  g'y = partial derivative of f with respect to y

  The program stops when quantity |Xn-Xn+1| + |Yn-Yn+1| < required precision.

  Final Xn, Yn give an approximate system solution.


REFERENCE: "Mathematiques en Turbo-Pascal part 1, By M. Ducamp and
            A. Reverchon, Editions EYROLLES, Paris, 1987".