% gradient field demo
% author: Fernando Guevara Vasquez
x =linspace(-1,1,20);
y =linspace(-1,1,20);
[xx,yy]=meshgrid(x,y);

zz = xx.^2-yy.^2;

% plot the surface
figure(1); clf;
h=mesh(xx,yy,zz); set(h,'edgecolor','k','facecolor','green','facealpha',0.5);

% plot the gradient field
figure(2); clf;
dx=2*xx; dy=-2*yy;

contour(xx,yy,zz); hold on; quiver(xx,yy,dx,dy); colorbar
