%% ----------------------------------------------------------------
clf;
rotate3d on;
hold on;

%% ----------------------------------------------------------------
%n = 4;
n = 20;
%n = 100;

xlo = -2.0;
xhi =  2.0;
nx  =  n;
dx  = (xhi - xlo) / nx;

ylo = -2.0;
yhi =  2.0;
ny  =  n;
dy  = (yhi - ylo) / ny;

[x,y] = meshgrid(xlo:dx:xhi, ylo:dy:yhi);

%% ----------------------------------------------------------------
%  w = y dx - x dy
% dw = 2 dx ^ dy

wx =  y;
wy = -x;

dw = 2 + x-x;

quiver(x,y,wx,wy);
figure; % Open up a second window
contour(dw);

