//Ex:3.18
clc;
clear;
close;
n=10;// number of isotropic elements
// d=y/4
// Do=1.789(4n*(d/y))
// Do=1.789(4n*(y/4y)=2n(1/4))
Do=1.789*(4*n*(1/4));
D0=10*log(Do)/log(10);// Directivity in db
printf("the Directivity = %f dB", D0);