% creates the function XoY where X is the X axis (to the right)
% and Y is the Y axis (up) and o denotes the Hadamard (or Schurr) product
%
% An image XoY has a positive mixed derivative; Exy > 0 or Eyx > 0
%
% F(x,y) = XoY
% In the continuous space, f(x,y) = xy
%
% Thus we have a saddle point. The diagonals are parabolas
L = 4;
M = 100;
[X,Y] = meshdom(linspace(-L,L,M), linspace(-L,L,M));
XY = X.*Y;
%mesh(XY)
% put things in the range [0..256)
XY = XY - min(min(XY));
XY = XY / max(max(XY)) *255; % should really be 256- or 255.99999999999