How to avoid negative intermediate guess in nlmefit

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Rui
Rui 2014 年 10 月 17 日
コメント済み: Rui 2014 年 10 月 22 日
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 年 10 月 18 日
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.
  3 件のコメント
Tom Lane
Tom Lane 2014 年 10 月 19 日
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 2014 年 10 月 22 日
Thank you!

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