[Ipopt] how to use the new_x flag in eval_* function?

Andreas Waechter andreasw at watson.ibm.com
Tue Mar 9 05:06:26 EST 2010

Hi QuanChang,

I just replied to an earlier posting by Jens, trying to explain it a bit 
clearer.  If you want to see an example, please have a look at the AMPL 
interface as I suggested in that email.



On Tue, 9 Mar 2010, lqc234 wrote:

> Hi all,
I noticed there is a  new_x flag in every eval_* function,the Ipopt's document said about the new_x flag:

The boolean variable new_x will be false if the last call to any of the evaluation methods(eval_*) used
the same x values.This can be helpful when users have efficient implementations that calculate multiple
outputs at once. Ipopt internally caches results from the TNLP and generally,this flag can be ignored.

However, I don't understand the flag very clearly.I want to understand the meaning of new_x flag and how I should use this flag in eval_* function. Anyone one can give me some explanations in detail? Thank you very much in advance!


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