(Newton插值多项式——cos x)帮忙看下这程序为啥不对好吗？谢谢老师和同学

function[P,G]=fun(xx,n)
x=[0.0,0.2,0.4,0.6,0.8,1.0,1.2];
y=[1.0,0.980067,0.921061,0.825336,0.696707,0.540302,0.362358];
t=[1.0,0,0,0,0,0,0];
A=[1.0,0,0,0,0,0,0];
for k=2:n
t(k)=y(k);
for j=(k-1):1
t(j)=(t(j+1)-t(j))/(x(k)-x(j));
continue
end
A(k)=t(1);
continue
end
P=A(n);
for i=n:2
P=P*(xx-x(i-1))+A(i-1);
end
G=abs(P-cos(xx));

下面代码有注释的地方是程序问题所在。按下面的程序运行结果是没问题的。更多问题请在此贴后回复。

代码:

clear;clc;
xx = 0.3;
n = 7;
x=[0.0,0.2,0.4,0.6,0.8,1.0,1.2];
y=[1.0,0.980067,0.921061,0.825336,0.696707,0.540302,0.362358];
t=[1.0, 0, 0, 0, 0, 0, 0];
A=[1.0, 0, 0, 0, 0, 0, 0];

for k=2:n
    t(k)=y(k);
    for j=(k-1):-1:1  %注意此处循环 (k-1):-1:1
        t(j)=(t(j+1)-t(j))/(x(k)-x(j));   
    end
    A(k)=t(1);
end
P=A(n);
for i=n:-1:2  %注意此处循环n:-1:2
    P=P*(xx-x(i-1))+A(i-1);
end
G=abs(P-cos(xx));