How to avoid negative intermediate guess in nlmefit

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Rui
Rui 2014-10-17
评论： Rui 2014-10-22
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 2014-10-18
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 2014-10-19
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.

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