x=[ -3 -1 0 2 5.5 7];
y=[3.3 4.5 2.0 1.5 2.5 -1.2];
p3=polyfit(x,y,3);
p4=polyfit(x,y,4);%次数
p5=polyfit(x,y,5);
xcurve=-3.5:0.1:7.2;%生成x的值
p3curve=polyval(p3,xcurve);
p4curve=polyval(p4,xcurve);%计算在这些x点的多项式
p5curve=polyval(p5,xcurve);
plot(xcurve,p3curve,\'--\',xcurve,p4curve,\'-.\',xcurve,p5curve,\'-\',x,y,\'*\');
lx=[-1 1.5];
ly=[0 0];
hold on
plot(lx,ly,\'--\',lx,ly-1.3,\'-.\',lx,ly-2.6,\'-\');
text(2, 0,\'degree3\');
text(2, -1.3,\'degree4\');
text(2, -2.6,\'degree5\');