function plotdata(x, y)
%plotdata(x,y) -- called by fig1.m & fig2.m

hold on;
p1 = find(y > 0);
p2 = find(y < 0);

plot(x(1, p1), x(2, p1), 'r+');
plot(x(1, p2), x(2, p2), 'bo');
