% Length of variable x and the Number of Entered data n
n = 11;
%===================================================
% Entered data
for i= 1:n
x(i)=input('Enter measured point: ');
z(i)=input('Enter depth: ');
R(i)=input('Enter Raduis: ');
rho(i)=input('Enter density: ');
end
gz = G*4*pi*R.^3/3.0.*z.*rho./(x.^2+z.^2).^1.5;
%===================================================
% Ploting the results
plot(x,gz,'r');
Assuming that you defined G before this.