lagrint.m

可以方便的调用这个函数

function yi=lagrint(x,y,xi)
dxi=xi-x;
n=length(x);
L=zeros(size(y));
L(1)=prod(dxi(2:n))/prod(x(1)-x(2:n));
L(n)=prod(dxi(1:n-1))/prod(x(n)-x(1:n-1));
for j=2:n-1
num=prod(dxi(1:j-1))*prod(dxi(j+1:n));
den=prod(x(j)-x(1:j-1))*prod(x(j)-x(j+1:n));
L(j)=num/den;
end
yi=sum(y.*L);