RE: enhancing Bode functionality

[Julian DeMarchi]

Hmmm.  The syntax is more or less

        [mag,phase,w] = bode(sys)

and this function will not generate any plots unless
you don't specify the left-side parameters.  So, rather
than write separate functions, why not simply use bode()
as above, and plot as a second step?

        [mag,phase,w] = bode(sys);
        semilogx(w, [mag phase]);

Or something of that nature.

Note, Matlab [mag,phase] arguments are MIMO-ised
(see 
http://www.mathworks.com/access/helpdesk/help/toolbox/control/ref/bode.shtml)

I'm not sure that Octave works the same way.
Also, the example in the link uses the function tf() 
which for Octave would be tf2sys().

- JD

-----Original Message-----
From: Steven Pavao [mailto:address@hidden
Sent: Monday, November 25, 2002 3:20 PM
To: address@hidden
Subject: enhancing Bode functionality


Hi,

I'm interested in improved bode functions for Octave,
so I'm doing a little work to try and get the
improvements I'm looking for.  Maybe some others have
also done some work, or would like to help me along in
my effort.

First, I've split the bode magnitude and phase
portions into two functions I'm calling bmag and
bphase.  This lets me get around a bug I was informed
of - one where plotting multiple curves on multiple
plots on a page does not work.  So now I can get
multiple curves onto either a magnitude or phase plot.
 Cool.  I'm really most interested in the magnitude in
general, though I would like to inspect the phase as
well.  Splitting them out just made sense for my
purposes, and for geting around the bug.

Now, I really want to plot the x axis in Hz, not
radians.  It's just the right thing for my my
purposes.  I have not done the work to do this.  I
wonder if the best approach is to just change what is
sent to gnuplot, although this may not suffice for the
feature I mention in the next paragraph...

The other annoyance is the auto-scaling of the axes. 
Many times when plotting, I want to compare multiple
curves, say, based on a varying coefficient(s).  So, I
don't want it to autoscale the axes in that case.  In
that case, I'd like to expose the axes "limits" to the
command line.  Of course, for the magnitude plot, I'd
like to specify these limits in dB and Hz.  If no
limits were specified, then autoscaling based on the
most recently plotted curve would be fine.

I would appeciate any tips or help.  I'm willing to do
some work and share my results.  I know this bode
functionality could be much more useful to my learning
process if I could just accomplish this small handful
of improvements, and others could probably benefit,
too.

best,
Steve Pavao


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-------------------------------------------------------------
Octave is freely available under the terms of the GNU GPL.

Octave's home on the web:  http://www.octave.org
How to fund new projects:  http://www.octave.org/funding.html
Subscription information:  http://www.octave.org/archive.html
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