function i = cannon_plot ( n )
x = -5 + 10 * rand ( n, 1 );
y = -5 + 10 * rand ( n, 1 );
z = 9 * x.^2 + 16 * y.^2 - 144;
ip = find ( z < 0 );
in = find ( z > 0 );
plot ( x(ip), y(ip), 'bo', x(in), y(in), 'ko' )
