y=[11.2 16.5 20.4 26.3 30.5];
pp1=spline(x,y) %三次樣條插值
poly3=polyfit(x,y,3) %三次多項式插值
poly4=polyfit(x,y,4) %四次多項式插值
x=1:0.2:5; %重新輸入待估值的x
y_pp1=interp1(pp1,x,'spline') %三次樣條估值
y_poly3=polyval(poly3,x) %三次多項式插值
y_poly4=polyval(poly4,x) %四次多項式插值
(2)
t=-6:0.01:6;
plot3(sin(t),cos(t),t,'--')