[ADMB Users] When to use mfexp

[John Sibert]

When in doubt, use mfexp(x). It invokes special code if exp(x) would be 
outside the range of a double, if memory serves (x > 60) or (x < -60). 
Usually a problem manifests itself as a nan somewhere if you are not 
using mfexp. The source code is in linad99/mfexp.cpp.

John

On 02/16/2012 01:04 PM, Mark Maunder wrote:
>
> Are there any guidelines in using mfexp
>
> The following two bits of code give different results in a negative 
> binomial model
>
>                               
> like=-log((1.0-pzi)*mfexp(log_negbinomial_density(Obs(i,8),ypred,tau)));
>
>                               
> like=-log((1.0-pzi)*exp(log_negbinomial_density(Obs(i,8),ypred,tau)));
>
> Is there any benefit from replacing
>
> mfexp(log_negbinomial_density(Obs(i,8),ypred,tau))
>
> with
>
> negbinomial_density(Obs(i,8),ypred,tau)
>
> Thanks,
>
> Mark Maunder
>
> IATTC fall workshop: Using Oceanography for Fisheries Stock Assessment 
> and Management
>
> 11-14 October 2011, La Jolla, CA
>
> http://www.fisheriesstockassessment.com/TikiWiki/tiki-index.php?page=Using+Oceanography+for+Fisheries+Stock+Assessment+and+Management+2011
>
> Head of the Stock Assessment Program
>
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>
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>
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>
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>
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>
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>
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>
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>
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>
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>
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>
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>
>
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-- 
John Sibert
Emeritus Researcher, SOEST
University of Hawaii at Manoa

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