Bode plot of individual poles and zeros

I need help with one of my homework problems. I am trying to plot the bode plot using the approximation method. Basically I need to use semilogx function to plot each individual pole and zero like in the screenshot attached.

What is the best approach to write this program?

[Walter Roberson]

Reminder: (s+10) is a pole at -10 not at 10 .

Answer 1

[Chunru]

z = 1000;
p = [10 10 100];
k = 200;

bode(zpk(z, p, k), 'k'); hold on

for i=1:length(z)
    bode(zpk(z(i), [], 1/z(i)), 'b--')   % (s-z(i))/z(i)
end

for i=1:length(p)
    bode(zpk([], p(i), p(i)), 'r:')         % p(i)/(s-p(i))
end

% You need to  use the approximation for each zero and pole to replace the
% bode above.  You may consider to write a simple approximation function
% for that purpose.