matlab 拉格朗日插值法

function Lagrange(X,Y,x0)
Len_y=length(Y);
Len_x=length(X);
if Len_y~=Len_x
    errorlog('維數不等');
else
    syms x;
    p=0;
    for i=1:Len_y
        q=1;
        for j=1:Len_x
            if j~=i
                q=q*(x-X(j))/(X(i)-X(j));
            end
        end
        p=p+q*Y(i);
    end
    
    simplify(p);
    
    if nargin==3
        sprintf('給定點處的函數值得近似值為: %f',subs(p,'x',x0))
    else 
        sprintf('所求的拉格朗日的插值函數為: ')
        p=collect(p);
        p=vpa(p,6),
    end
end
end

    
        
        
    
                
 clc;
X=[2 2.5 4];
Y=[0.5 0.4 0.25];
Lagrange(X,Y);