High Pass Filter - First Order AR Process (Matlab 2012a)

Program:
clc;
clear all;
n = input('Enter the no. of values:');
colr = ['g','b','r','k'];
for i = 1:n
    r = input('Enter the value for r:');
    d0 = 1+(r*r)+ 2*r;
    w1 = 0:0.001:pi;
    d1 = 1+(r*r)-(2*r.*cos(w1));
    ps = d0./d1;
    hold on;
    semilogy(w1,ps,colr(i));
end
xlabel('Frequency(Units of pi)');
ylabel('Power Spectrum');
title('Response of High Pass Filter');
legend('r=.5','r=.75','r=.9');

Output:
 
Enter the no. of values: 3
Enter the value for r: -0.5
Enter the value for r: -0.75
Enter the value for r: -0.9

Output Graph: