       Re: bode diagram

• To: mathgroup at smc.vnet.net
• Subject: [mg57151] Re: bode diagram
• From: "Mariusz Jankowski" <mjankowski at usm.maine.edu>
• Date: Thu, 19 May 2005 03:08:22 -0400 (EDT)
• Organization: University of Southern Maine
• References: <d64fjl\$9gl\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Bob, the argument of your function h must be I * s in both the magnitude
plot and the phase plot. You are therefore making a mistake in ALL of your
magnitude plots.

Mariusz

>>> DrBob<drbob at bigfoot.com> 05/14/05 5:15 AM >>>
I used the code below for each example at the link:

http://www.swarthmore.edu/NatSci/echeeve1/Ref/Bode/BodeRules.html#Examples

In several cases I got what appears to be the same result as pictured at the
link, but in other cases I got very different plots. The fourth example is
particularly strange. Am I doing this wrong?

I'm plotting magnitude and phase on a single plot in each case, and I'm ONLY
plotting the exact curves -- assuming I have the right formulae for them. I
see no point in approximate plotting techniques, with exact plots readily
available.

Needs["Graphics`Graphics`"]
SetOptions[LogLinearPlot, PlotStyle ->
{Red, Blue}, PlotRange -> All,
ImageSize -> 500];
db = 20*Log[10, Abs[#1]] & ;

Clear[h]
h[s_] = 100/(s + 20);
LogLinearPlot[{db[h[s]], Arg[h[I*s]]*(180/Pi)},
{s, 1, 10^3}];

h[s_] = (100*s + 100)/(s^2 + 110*s + 1000);
LogLinearPlot[{db[h[s]], Arg[h[I*s]]*(180/Pi)},
{s, 10^(-2), 10^4}];

h[s_] = 10*((s + 10)/(s^2 + 3*s));
LogLinearPlot[{db[h[s]], Arg[h[I*s]]*(180/Pi)},
{s, 10^(-1), 10^3}];

h[s_] = (-100*s)/(s^3 + 12*s^2 + 21*s + 10);
LogLinearPlot[{db[h[s]], Arg[h[I*s]]*(180/Pi)},
{s, 10^(-2), 10^3}];

h[s_] = 30*((s + 10)/(s^2 + 3*s + 50));
LogLinearPlot[{db[h[s]], Arg[h[I*s]]*(180/Pi)},
{s, 10^(-1), 10^3}];

h[s_] = 4*((s^2 + s + 25)/(s^3 + 100*s^2));
LogLinearPlot[{db[h[s]], Arg[h[I*s]]*(180/Pi)},
{s, 10^(-1), 10^3}];

Bobby

From: Pratik Desai <pdesai1 at umbc.edu>
To: mathgroup at smc.vnet.net
References: <200505120633.CAA08967 at smc.vnet.net>

David Park wrote:

> I'm fairly certain it could be done with Mathematica if you would only
tell
> us what a bode diagram is and give us some sample data of function that
you
> want to plot in the diagram.
>
> David Park
>
> From: GaLoIs [mailto:lanellomancante at inwind.it]
To: mathgroup at smc.vnet.net
>
>
> hi, like plotting simple bode diagrams of systems. could you give me some
> information about it? i can do it with another program, but i'd like to
see
> how mathematica works
> thank you
>
>
>
>
>
>
>
Here is a nice example from a website I found.

*http://www.swarthmore.edu/NatSci/echeeve1/Ref/Bode/Bode.html*

--
DrBob at bigfoot.com

```

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