[Ipopt] what's the meaning of the new_x flag in eval_* function in Ipopt?

[lqc234]

Hi everybody,hi Andreas:

 I noticed that there is a  new_x flag in every eval_* function,the 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.

I don't understand the meaning of this section very cleary.I guess the meaning is that we can calculate the value,grandient,and hessian for my function in only one of the eval_* function.If so,how should I write my program? Would you please explain the new_x flag in detail?Thank you very much in advance!

Regards,

LiuQuanchang
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