[Ipopt] Cutting back alpha due to evaluation error

[Stefan Vigerske]

Hi,

that the point cannot be evaluated is already recognized in the function 
evaluation code (probably to GAMS AD library in your case), the Ipopt 
interface then just signals to Ipopt that the given point could not be 
evaluated.
Unfortunately, I do not see a place in the code that would print the 
point before or after calling the evaluation routines.
If you can modify Ipopt code, then try to activate the 
DBG_PRINT_VECTOR's in 
IpoptCalculatedQuantities::trial_primal_infeasibility().

Stefan


> Hi,
>
> I have an NLP for which I often get the message
>
> 	"Warning: Cutting back alpha due to evaluation error".
>
> I know that this has something to do with constraints that are not well
> defined at the current point (like sqrt of negative numbers etc.).
>
> Is there any chance to analyze at which constraint in the model the
> problems occurs? I thought I could find some "inf" or "nan" values in
> the higher output levels but I didn't find anything.
>
> Thanks in advance,
> Martin
>
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>


-- 
Stefan Vigerske
Humboldt University Berlin, Numerical Mathematics
http://www.math.hu-berlin.de/~stefan