x=1:10;
y=[4.9,3.3,4.2,4.2,5.7,6.5,7.7,9.4,14.7,19.0];
a=polyfit(x,y,2);
b=polyfit(x,y,3);
c=polyfit(x,y,4);
xx=1:0.1:10;
yy1=polyval(a,xx);
yy2=polyval(b,xx);
yy3=polyval(c,xx);
plot(x,y,'*b')
hold on
plot(xx,yy1,'-r',xx,yy2,'-g',xx,yy3,'-y')
title('2,3,4次曲线拟合')
xlabel('变量x')
ylabel('变量y')
legend('y','yy1','yy2','yy3')