[Ipopt] Obtaining maximum change in NLP variables on every iteration.

[Juan Arrieta]

Hello,

I would like to display the index and delta of the NLP variable that changes the most during every iteration.

I considered reading the `IpoptData` pointer provided to the `TNLP::intermediate_callback()` method. For example, I expected the following to give me the maximum change:

     auto max_delta_x = ip_data->delta()->x()->Max();

Unfortunately this does not seem to be the proper usage, as `ip_data->HaveDeltas()` returns `false` on every iteration.

How would you advice to obtain this information?

Thank you!

  - JA

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Juan Arrieta, PhD | Mission Design
Outer Planet Mission Analysis Group
NASA Jet Propulsion Laboratory