function [xi,yi] = find_intersection(x,y,w)
%[xi,yi] = find_intersection(x,y,w) finds the intersection 
%  point(s) of the two curves given by the vectors 'y' and 'w'.
%  The vector 'x' is the collection of x-axis inpedendent data 
%  points.  All vectors must be the same length.  
%  Note: this function does not work on matrices yet.
%
%  Example use:
%    x=0:0.01:3; y=x.*sin(x); w=0.07*exp(x)+0.4; 
%    [xi,yi]=find_intersection(x,y,w);
%    plot(x,y,'b',x,w,'g',xi,yi,'ro'); grid on;
%
%  Last Edit by Colin Joye, 6/27/03F

% n is the index of the point just before intersection.
n = find( abs( diff( ((y-w)>0)-((y-w)<0) ) )>0 );

% compute line slopes:
m1 = ( y(n+1) - y(n) )./( x(n+1) - x(n) );
m2 = ( w(n+1) - w(n) )./( x(n+1) - x(n) );

% compute line points:
b1 = y(n) - m1 .* x(n);
b2 = w(n) - m2 .* x(n);

% compute line intersections:
xi = (b2 - b1) ./ (m1 - m2);
yi = m2 .* xi + b2;
% ------------- END find_intersection.m -----------------