how can I fit a curve in bode digram?

Hello,

I want to fit a curve using lsqcurvefit from a bode diagram of a transfer function. I do not have x data and y-data but only the transfer function. how can I find x-data and find y-data from a bode diagram?

or is there any other ways to find a fir curve from a transfer function?

Answer 1

[Shashank Prasanna]

if you have the transfer function then all you need to do to get the curve is call the bode function:

http://www.mathworks.com/help/control/ref/bode.html

How do you have the bode figure? is it a matlab figure? If so then you can extract the values from the figure.

What are you trying to fit to the curve?

[Shashank Prasanna]

I think there are better ways to do what you are tying to do. A commonly used method is balanced order reduction where you can specify the lowest order you want to represent your system:

http://www.mathworks.com/help/control/ref/balred.html

Is you have Simulink Design Optimization toolbox then there are graphical ways to do what you are tying to do:

http://www.mathworks.com/help/sldo/ug/frequency-domain-design-requirements-gui.html

Answer 2

[navin haghighizadeh]

I am trying to fit the curve with reduced kind transfer function. the original transfer function has 10 poles and 10 zeros. I found the x-data and y-data but I cannot use lsqcurvefit.

[Shashank Prasanna]

Please see my comment above. If you'd like to respond to my answer or comment, please do so right below it instead of creating a new answer. This will make the answer hard to track for others who have the same question as yours.