I am trying to write a script that graphs the Lagrange interpolation of a given set of points.
The following is the code, which logically seems to be correct, but it keeps throwing an error I do not understand and I am unsure how to fix it as I am unfamiliar with MATLAB's symbolic computation capabilities and syntax.

Code:

syms x
xanchor=input('x values (enter in vector form): '); %x values of interpolating points
yanchor=input('y values (enter in vector form): '); %y values of interpolating points
N=length(xanchor);
P=ones(1,N);
for i=1:N
for j=1:N
if i~=j
P(i)=P(i)*(x-xanchor(j))/(xanchor(i)-xanchor(j));
end
end
end
f=0;
for i=i:N
f=f+yanchor(i)*P(i);
end
x1=min(xanchor);
x2=max(xanchor);
x=x1:.1:x2;
plot(x,f)
hold on
scatter(xanchor, yanchor)
hold off

The error I am getting is:

??? The following error occurred converting from sym to double:
Error using ==> mupadmex
Error in MuPAD command: DOUBLE cannot convert the input expression into
a double array.


If the input expression contains a symbolic variable, use the VPA
function instead.


Error in ==> boom at 9
P(i)=P(i)*(x-xanchor(j))/(xanchor(i)-xanchor(j));

Any help is greatly appreciated.