clear
x = [0:20:500]';
x1 = [0:500]';

f = sin(x).*(1+x)./(1+x.^2);
f1 = interp1(x,f,x1);       % linear interpolation function

f2 = spline(x,f,x1);        % cubic interpolation function

figure(1)
plot(x,f,'o',x1,f1)
xlabel('x')
ylabel('f')

figure(2)
plot(x,f,'o',x1,f2)
xlabel('x')
ylabel('f')