Octave and multiple Bode plots - octave

Question

I'm teaching myself Octave and as a motivational exercise am attempting to create some Bode plots. I'd like to create a plot that has multiple curves for different values of a parameter in a transfer function, for example the time constant of a simple RC filter. I'm trying to do it as follows:
tau = [1,2,3]
for i = tau
g(i) = tf(1,[tau(i),1])
endfor
bode(g(1),g(2),g(3))
But it doesn't work, I get the error
error: octave_base_value::imag (): wrong type argument `struct'
However, it works fine if there are not multiple arguments to the bode command and the last line is simply:
bode(g(1))
Any advice as to where I've gone wrong would be appreciated - is there a better way to do what I want to do?

Answer 1

I was able to do it with the following sequence (with octave 3.2.4 on debian):
bode(g(1))
set (findobj (gcf, "type", "axes"), "nextplot", "add")
bode(g(2))
bode(g(3))
The second command is similar to hold on but it works when there are subplots; I found it here.

Answer 2

Using your own code:
subplot(211), hold on
subplot(212), hold on
tau = [1,2,3]
for i = 1:length(tau),
g(i) = tf(1,[tau(i),1]);
bode(g(i))
endfor
The problem with this solution is that you cannot identify a specific plot. You cannot access figure properties through bode() function directly.
Here then a plausible solution to bring you colorful plots:
colorsplot = ["b","m","g"]
tau = [1,2,3]
g = tf(1,[tau(1),1]);
[mag, ph, w] = bode(g);
subplot(211), semilogx(w,20*log(mag)), hold on
subplot(212), semilogx(w,ph), hold on
for i = 2:length(tau),
g = tf(1,[tau(i),1]);
[mag, ph, waux] = bode(g,w);
subplot(211), semilogx(w,20*log(mag),colorsplot(i))
subplot(212), semilogx(w,ph,colorsplot(i))
endfor