matlab中怎样将散点用光滑曲线连接起来??

1 x=[1 2 3 4 5 6];
2 y=[3 6 8 13 31 24];
3 xx=linspace(1,6);
4 yy=spline(x,y,xx);
5 plot(xx,yy,'r',x,y,'o')