How to write a custom (exponential rise) fitting function?

[Thang Nguyen]

Hi,

I have a set of data which is in a shape of exponential rise function. I cannot find any fitting VI can fit this data set so I would like to build one.

I know that my data set is Y = A - B*exp(-C*X). But I don't know how should I start to make my VI can find the fit automatically.

I highly appreciate your time on reading and answering my questions.

Best regards,

Thang

[crelf]

I assume Y is an array, but which of A, B and C are scalars/arrays?

[Thang Nguyen]

Crelf : X is an arry

[ShaunR]

Are using the "Base Package"?

[mzu]

Are using the "Base Package"?

This particular implementation of Exponential fit was known to have problems when data falls below 0. Use http://zone.ni.com/reference/en-XX/help/lv/71/gmath/Levenberg_Marquardt/ instead.

I am not a great fan of express VIs, but potentially you can use Curve Fitting.vi express VI. Both require something more then base package.

An overkill for such a simple problem, but you can also use

[Thang Nguyen]

Hi,

I tried with base package but it doesn't work in my case.

I attach here the graph and data set.

Thang

TestFitData.txt

[Thang Nguyen]

I found the nonlinear curve fitting VI and play with it, but by some reason it doesn't work. I attach it here so you may can try it.

Select TestFitData.txt as source

TestFitData.txt

TestFit.vi

[vugie]

I found the nonlinear curve fitting VI and play with it, but by some reason it doesn't work. I attach it here so you may can try it.

Select TestFitData.txt as source

Can't you just move the data to domain where expotential fitting works? Like this: