function f = Language(x,y,x0)
syms t;
if(length(x) == length(y))
    n = length(x);    
else
    disp('x和y的維數不相等！');
    return;
end                                      %檢錯

f = 0.0;
for(i = 1:n)
    l = y(i); 
    for(j = 1:i-1)
        l = l*(t-x(j))/(x(i)-x(j));      
    end;
    for(j = i+1:n)
        l = l*(t-x(j))/(x(i)-x(j));      %計算拉格朗日基函數
    end;

    f = f + l;                           %計算拉格朗日插值函數      
    simplify(f);                         %化簡

    if(i==n)
        if(nargin == 3)
            f = subs(f,'t',x0);          %計算插值點的函數值
        else
            f = collect(f);          %將插值多項式展開
            f = vpa(f,6);                %將插值多項式的系數化成6位精度的小數
        end
    end
end