Please someone solve the error of unexpected error at x=D./2f

clear all;

close all;

clc;

n=1.49;

D=0.1:.02:0.3;

f=0.2;

x=D./2f;

NA=n*sin(atan(x));

plot(D,NA);

xlabel('Diameter of lens');

ylabel('Numerical Aperture');

title('Variation in numerical aperture with increase in diameter')

Answer 1

[Cedric]

What is 2f? Is this what you are trying to compute?

 x = D ./ (2*f) ;