% fig 10.9a Bode Plots
%
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
plot(f,r,'k-')      % gain vs freq in Hz
% replace with   plot(f,phi)         for phase plot 
% replace with   plot(f,20*log10(r)) for decibels 
% replace with   plot(w,r) for       gain vs radian freq