[ADMB Users] checking for uninitialized parameters

[John Sibert]

Dave recently sent around some code to check for incorrectly variables 
in an admb template. The code is integrated into the derivative checker. 
To use it, run you application to check the derivatives before the first 
function evaluation; ie "my_app -dd 0". Enter '0' a the the prompt  "to 
check for unitialized variables enter 0)".

This code is currently only available for those who build their own admb 
libraries from source in. Check out revision 759. It will eventually 
find its way into the next stable release. It has not been extensively 
tested.

Incorrectly initialized variables can lead to unpredictable results. An 
obvious example is:
> PARAMETER_SECTION
>   init_vector x(1,5)
>   number ssum
>   objective_function_value f
> PROCEDURE_SECTION
>   ssum+=norm2(x-1.0);
>   f=ssum;
The first time the code in the PROCEDURE_SECTION is executed, the value 
of ssum is not guaranteed to be zero. A more correct version would be:
> PROCEDURE_SECTION
>   ssum = 0.0;
>   ssum+=norm2(x-1.0);
>   f=ssum;
Thanks to an ADMB user for bringing this to our attention and to Dave 
for fixing it.

Cheers,
John

-- 
John Sibert
Emeritus Researcher, SOEST
University of Hawaii at Manoa
Honolulu HI (GMT-10)
808-294-3842

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