How to avoid negative intermediate guess in nlmefit

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Rui on 17 Oct 2014

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Commented: Rui on 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 on 18 Oct 2014

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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 on 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 on 22 Oct 2014

Thank you!

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