Putting transfer function expression in the title of a bode plot

Hi Consider the following code snippet:

num=[1 2];
den=[1 7 49];
trans=tf(num,den);
tran=evalc(trans);
bode(trans)
Title=('Bode plot of:', tran)

I want to put the transfer function in the title in rational form as a function of s. I got it working but the title is cut off at the top of the figure window and maximising the window does not help. How can I adjust the vertical position of the title so that it will all be visible. Or is there a better way of converting the tf expression to a string variable that can be passed to the title. Many thanks for any help you can give me. Regards. Thomas

Answer 1

[Star Strider]

I couldn’t reproduce your results with your code (the evalc call threw an error in R2017a), so I used the Symbolic Math Toolbox to create the transfer function for the title.

The Code —

num=[1 2];
den=[1 7 49];
trans=tf(num,den);

syms s 
n = sym(num);
d = sym(den);
ns = poly2sym(n,s);
ds = poly2sym(d,s);
tfsym = ns/ds;
tftitle = latex(tfsym);

figure(1)
bode(trans)
title(sprintf('Bode plot of: $$ %s $$', tftitle), 'Interpreter','latex')

The Plot —

[Thomas Gahan]

Hi Star Strider Thank you so much for your reply, much appreciated. It worked perfectly in the 2010b version also. I have included the code I was using as I might not have had it correct when I sent it to you yesterday evening as I was working from memory. Once again thank you so much. Regards Thomas clc num=[1 2]; den=[1 7 49]; trans=tf(num,den); tran=evalc('trans'); bode(num,den) title(['Bode Plot of',tran])

[Star Strider]

As always, my pleasure.

The evalc call is an option I had not considered. I could not get it to display correctly either, the reason I decided to use the Symbolic Math Toolbox and let it create the appropriate LaTeX code.

Answer 2

[Andoni Medina Murua]

Hi Star Strider, thanks for your reply. Solution works for me but it gives me this warning:

Warning: Error updating Text.

String scalar or character vector must have valid interpreter syntax:

$$

\frac{\frac{4882746935387697\,s}{35184372088832}+\frac{2444881814469459}{274877906944}}{s^2+\frac{2602689349497067\,s}{35184372088832}+\frac{1385815694070911}{1099511627776}}

$$

What's the issue, could you help me? Just tried using your example, it gives the same error.

thanks, regards

Andoni

[Star Strider]

This works correctly when I run it:

tftitle = '\frac{\frac{4882746935387697\,s}{35184372088832}+\frac{2444881814469459}{274877906944}}{s^2+\frac{2602689349497067\,s}{35184372088832}+\frac{1385815694070911}{1099511627776}}';
num=[1 2];
den=[1 7 49];
trans=tf(num,den);
syms s 
n = sym(num);
d = sym(den);
ns = poly2sym(n,s);
ds = poly2sym(d,s);
tfsym = ns/ds;
% tftitle = latex(tfsym);
figure(1)
bode(trans)
title(sprintf('Bode plot of: $$ %s $$', tftitle), 'Interpreter','latex')

You did not correctly format the string (that I call ‘tftitle’ here) when you posted it, so I have no idea what the original problem with it could be.

[Andoni Medina Murua]

Hi Star Strider

Thanks for your reply. I copy paste what you sent and still I get the same warning, maybe it's linked with the Matlab version? I'm running 2018b.