randn('state', 0); rand('state', 0);
ndat1 = 50; ndat2 = 150; ndata = ndat1+ndat2;
sig1=1.0;
sig2=0.5;
grp_label=[ones(1,ndat1) 2*ones(1,ndat2)];

x1=sig1*randn(1,ndat1);
y1=sig1*randn(1,ndat1);

r2=5+rand(1,ndat2);
t2=2*pi*rand(1,ndat2);
t2=sort(t2);
x2=r2.*cos(t2);
y2=r2.*sin(t2)-2;

x=[x1 x2];
y=[y1 y2];

figure(1)
plot(x,y,'.')
%   scatter(x,y,25,grp_label)