Hi, I am interested in fitting some data (intensity as a function of time) to a sum of exponentials convolved with a gaussian instrument response function (IRF). I will use the Nonlinear Curve Fit LM instance of the Nonlinear Curve Fit VI and therefore intend to provide a model VI with the right connector pattern that provides an array containing the model (decay convolved with IRF. But ... I think that the model will change with each iteration of the least squares search not only because the parameters a in f(X,a) change (the normal situation) but also because of the convolution with the gaussian IRF. How do I get the levenberg Marquardt routine to feed the parameters a back into the model calculator for each iteration. Or am I missunderstanding something fundamental here.Thanks so much -nd

LabVIEW

Nonlinear curve fitting and convolution

Scarpa wrote:
I am working on a VI which takes in account an IRF by a Gaussian function but I am facing the problem of convonlution.

OK first of all, please don't use acronyms without detailed explanation. According to Google, IRF could mean anything from the "International Rectifier corporation" to the "International Rhino Foundation")

OK, looking at your VI now. Way too much code! If you want array elements in order, you don't need to wire the indiced to index array. If you are autoindexing, you don't need to get the size and wire N. You should also autoindex once and branch the wire inside the loop.

You probably get better performance with plan G code, for example the three exponential as well as the gaussian can be calculated in parallel.

I don't understand your gaussian pulse calculation. What are a and b defined as integers??? Why is the gaussian also shifted by x0?

Do you have some typical data and good parameter estimates?

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