How can I plot a function i can´t define before calculating it?

X = [1,2,4,5, 17, 34];
Y = [8,14,25,1,-3,27];
syms x;
sum = 0;
for i = 1: length(X)
   u = 1;
   l = 1; 
   for j = 1: length(X)
       if j ~= i
           u = u * (x - X(j));
           l = l * (X(i)-X(j));
       end
   end
    sum = sum + ((u/l)*Y(i));
end
disp(simplify(sum)); 
fplot(sum(x));

I´m trying to use Lagrange´s method for finding a polynomial, but after finding it i can´t plot the function "sum".

Is there a way to do that?

Answer 1

[David Hill]

fplot(sum);

[Jose Ramirez]

Thanks! I had tried it but didn´t notice until now that the issue is actually the scale, it somehow seems off.