Support for new NLP in COPT 7.2.5

[Salancelot]

In COPT 7.2.5, NLP is supported, but now only in C API, see General Nonlinear Programming (NLP). Is there any plan to support it in pyoptinterface?

[metab0t]

Definitely yes!

The NLP API of COPT and Gurobi are all based on expression tree and will be supported in PyOptInterface after careful investigation.

[Salancelot]

@metab0t by the way, is it possible to formulate an NLP problem using POI.ipopt and then write it to a .nl file? I didn't fild a API related to "write".

[metab0t]

Writing NL file is not supported now.

I am currently working on a unified (and more intuitive) NLP functionality to support NLP with COPT, Gurobi and Ipopt in PyOptInterface. Keep tuned!

The new NLP interface can capture the expression graph of each constraint and objective that makes writing NL file possible.

However, supporting NL file is not a easy task and should belong to a more ambitious project to achieve seamless interoperation between POI and the AMPL ecosystem, and I have no plans to start it now.

[Salancelot]

Writing NL file is not supported now.

I am currently working on a unified (and more intuitive) NLP functionality to support NLP with COPT, Gurobi and Ipopt in PyOptInterface. Keep tuned!

The new NLP interface can capture the expression graph of each constraint and objective that makes writing NL file possible.

However, supporting NL file is not a easy task and should belong to a more ambitious project to achieve seamless interoperation between POI and the AMPL ecosystem, and I have no plans to start it now.

Thanks for the detailed explanation! Fully understand the complexity of NL file support, and I'm excited about PyOptInterface's future NLP capabilities. The current functionality already meets my needs, and your roadmap prioritization makes perfect sense. Looking forward to the updates!

[rschwarz]

This may be off-topic here, but Pyomo does support exporting models to NL format, all by itself (without using a solver).

[metab0t]

This may be off-topic here, but Pyomo does support exporting models to NL format, all by itself (without using a solver).

@rschwarz Yes. The NL file writer and solution reader are the primary method to communicate with solvers in Pyomo (as an open source alternative of AMPL), so it has a powerful expression system and NL export functionality from the very beginning. The direct and appsi-persistent interfaces are added later to overcome the drawbacks of file-based IO. (My knowledge of Pyomo might be inaccurate)

[rschwarz]

I just wanted to point it out to users who might need NL export today, not as a suggestion for POI to follow 😃