画Beta分布图
X=0:0.01:1;

y1 = betapdf(X, 40, 40 );
figure;
plot(X,y1,'Color','g');

hold on;
y2 = betapdf(X,100,100);
plot(X,y2,'Color','r');

hold on;
y3 = betapdf(X,20,40);
plot(X,y3,'Color','b');