How to avoid negative intermediate guess in nlmefit

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Rui
Rui le 17 Oct 2014
Commenté : Rui le 22 Oct 2014
Hello everyone,
when I use nlmefit, it always comes up with some negative guess after a few iterations, these negative values crash my ODE solver. Is there a way to avoid this?
The easiest way I can think of is to set lower bound for fitted parameters, however, I cannot figure out how to do that with nlmefit.
Thank you!
Rui

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Tom Lane
Tom Lane le 18 Oct 2014
If a parameter P needs to be positive, sometimes people will instead estimate a parameter logP and then use exp(logP) in place of P in their function.
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Tom Lane
Tom Lane le 19 Oct 2014
I'd forgotten about this parameter. Yes, I'd use that to specify a log transform and let the function take care of converting the covb matrix.
Rui
Rui le 22 Oct 2014
Thank you!

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