Fitting with integral functions

[photoon]

Hi,

I try to fit the data with integral functions.  It is impossible to obtain the analytical solutions of the integrations. 

The integration is Integral[ ( T - abs[x] ) f(x) dx, T, -T ] 

Here, f(x) is one of the autocorrelation functions for different model systems.

Thanks

Doogie

[Matt-J]

Hi Doogie,

I'm not exactly sure what you are asking here. Could you clarify what you are looking for assistance with?

Thanks,

[photoon]

Hi, Matt,

I want to do fitting with the integral form. As I said, it is impossible to solve the integration so I cannot obtain the functional form without integral. How can I implement this task in Labview? Do you have any examples?

Thanks

Doogie

[Matt-J · Accepted solution]

Hi Doogie,

We certainly have integration and curve fitting VIs build into LabVIEW. For example, you can find several kinds of integrators in the Mathematics >> Integration & Differentiation palette. Also, if you are using our Control Design & Simulation Toolkit, this has integration built in as well. However, since you are dealing with an equation as opposed to sampled signals, I would begin by programming your equation in LabVIEW. Take a look at this forum thread that discusses this and has some example code posted. 

Once you have programmed the equation and can generate an array of points for your range, you could try inputting these into an integration function like the "Integrate x(t).vi" and then use a curve fitting function like the "General Polynomial Fit.vi" to generate a fitting equation for it. I would try getting started this way. Please let me know if I am not addressing the functionality you are interested in.

Best regards,

[altenbach]

See also this recent discussion.

[photoon]

Hi Matt,

I am confused about your explanation. The function which is supposed to be integrated has parameters. I don't know how to generate an array of points because these parameters should be determined by fitting later. I use nonlinear curve fit vi. Therefore, the problem is to express the integral of functions with labview functions. How do I do it with numerical integration? Please give me more advices.

- Doogie

[altenbach]

You would calculate a sufficiently dense array over the inner function between the integration boundaries, then do a numeric integration to get the integral.

[photoon]

Can I do that with literal parameters?

[altenbach]

What are literal parameters?

[photoon]

What I mean is the fitting parameters in the function which is to be integrated.