function result = slope(x1,y1,x2,y2)
%slope calculate slope of a line given two points on that line
%
% consumes: x1, y1   the coordinates of the first point
%           x2, y2   the coordinates of the second point
%
% produces: result, the slope of the line 
%
%
% examples:
%       >>  slope(1,1,9,5)
%       ans =
%            0.5
%       >>  slope(0,-5,-5,5)
%       ans =
%            -2
%       >>   
%  P. Conrad for CISC106, Sect 99, 09/15/2007

  result = (y2 - y1) / (x2 - x1);
  return;
end