% Routine 10.1 Bode Plots
%
% JV (10/22/2002): modified with subplots
%
fmin = 0;            % min freq (in Hz) to view
fmax = .5;           % max freq (in Hz) to view
df = 0.01;           % step size
f = fmin:df:fmax;    % frequency vector
w = 2*pi*f;          % radian freq vector
s = w*i;               
N = s.*s  + 1;       % numerator of transfer fn
D = s.*s  + s + 1;   % denominator
H = N./D;            % transfer fn
r = abs(H);          % gain at freq w
phi = angle(H);      % phase lead
subplot(2,2,1)
plot(f,r)            % gain vs freq in Hz
subplot(2,2,2)
plot(f,phi)          % phase plot 
subplot(2,2,3)
plot(f,20*log10(r))  % decibels 
subplot(2,2,4)
plot(w,r)            % gain vs radian freq