how do i fit an exponential to a waveform?

[ConfusedJason]

I have a waveform that I want fitted with an exponential.  First of all, I'm having trouble trying to timeshift the waveform. I'm trying to do this by modifying the waveform attributes but this does not seem to be work.  Once I do that I need to convert the waveform into something that the exponential fitting function will accept.  Is there any easy way to do this? 

[ConfusedJason]

It looks like the best way to approach this is to convert my waveform to (x,y) points, but I can't for the love of god figure out what kind of output that function is giving.  If I treat the output as an array of clusters it gives me an error saying that it is a cluster, and if I treat the output as a cluster of arrays, it gives me an error saying that it is a 1-D array.  What exactly is it? 

[altenbach]

Are the points equally spaced in x? Can you attach a small VI that contains your waveform as a diagram constant?

[ConfusedJason]

Yes, they're equally spaced.  I attached an example of a waveform I want to fit.  The part I want to fit is the 2nd "section"

[altenbach]

After your graph contains data, right-click on it and select "Data operations...Make current values default". Save it and attach it again. Thanks!

[ConfusedJason]

Ah, I was about to upload the fixed file just as I read your post 🙂

[altenbach]

Sorry, I no longer have LabVIEW 6.1. LabVIEW 7.0 and higher actually has an express VI for fitting, including single exponentials with offset.

The Nonlinear Lev-Mar fit contains your desired function by default, so you can use it "out-of-the-box". Just give it some reasonable initial estimates.

It seems to work fine. I have attached it as an image of the code and output graph. Just wire it up as shown. 😉

Message Edited by altenbach on 10-31-2005 04:59 PM

[ConfusedJason]

Neat.  I'll try that out.  Thanks for the help!