Curve Fitting to high order exponential function

Hello everybody, this is my first question here.

What I was trying to do is to fit an exponential function to a data. I already tried Matlab's Curve Fitting Tool, however it only fits exponential functions up to 2nd order. My data is more complex than that unfortunately, therefore 2nd order fit doesn't give me good result. Do you know any other tools or methods that I can use in Matlab to make the exponential fitting higher than 2nd order ?

Thanks in advance

Anil

[dpb]

You can fit any model you can write; however, I'd ask what the purpose of this fitting is? If for interpolation, you'll likely do better with a spline; if for model estimation then is there a candidate model based on first principles?

IOW, the last thing to do is to simply start throwing more terms into an equation and hoping for good result.

Seeing the data would possibly lead to better and more specific suggestions.

[John D'Errico]

I wish I could up-vote a comment. I would do so for dpb's comment were that possible.

[ANIL ALAN]

Hello dpb

Thanks for the comment. Let me go a little deeper into the problem. I am going to design a controller for a physical system. Before going into to design phase, I would like to create a nice model. A part of this system is a BLDC (as actuator). I would like to create motors model by its response to a step input. I am using its own driver card and I see that when I first introduce the step position change command, driver pass the command through some kind of filter to smoothen harsh change. Eventually, I would like to model this pre-filter hoping to fit output to a linear system. Its output looks alike a linear filter of high order with most of the states zero. I attached the output data to comment.

Answer 1

[Rakesh Chavan]

Hi Alan,

Have you tried using the System Identification APP in MATLAB. It the App can be used for identifying linear models given data which I think you want to achieve. Documentation for the app can be found at the following link:

http://www.mathworks.com/help/ident/gs/identify-linear-models-using-the-gui.html

There are other functions like 'iddata' and 'ssest' where given data and order we can obtain a state space model for the plant. Kindly refer to the following link:

http://www.mathworks.com/help/mpc/gs/system-identification-toolbox-models.html

Hope this helps.

[ANIL ALAN]

Thank you, that is the answer I am looking for.