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Three exponential fit with curve fitting toolbox

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Katéri Tremblay
Katéri Tremblay on 4 Nov 2020
Hi,
I'm using the Curve Fitting Toolbox in MatLab and I don't see a way to do a three term exponential fit. Is there a way I can do it? If the custom equation can be helpful, how can I use it for that kind of problem? And why MatLab Curve Fitting Toolbox doesn't offer the three term exponential fit?
Best regards,
Kateri.

Answers (2)

Asad (Mehrzad)  Khoddam
Asad (Mehrzad) Khoddam on 4 Nov 2020
In the toolbox, there is an option to define a custom model.
  2 Comments
Asad (Mehrzad)  Khoddam
Asad (Mehrzad) Khoddam on 4 Nov 2020
If you have any ideas about the cofficients, you can set a lower and upper values for them instead of -Inf and Inf

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John D'Errico
John D'Errico on 4 Nov 2020
You an always define your own custom model using fittype. Nothing stops you. But multiple term sums of exponential fits are often difficult to estimate well. Personally, if I was writing the curvefitting toolbox, I would leave it out too, just because most people lack good enough data or good enough starting values. So I would force the person who really wants to do that, to also know enough about what they are doing to have even a remote chance of success.
But nothing stops you from doing as you wish. As I said though, good data and good starting vaues will be crucial. If you allow it to choose its own random starting values, then expect possibly total crap for a result.

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