The OPAL Discussion Forum

[Renato Bellotti <renato.bellotti AT psi.ch>]

Dear Jochem,

Thanks for your answer.

Did you verify that the solutions you found with the surrogate model are also solutions with OPAL? (That is run the OPAL-simulation with that input and verify that it fulfils all constraints).

I have fed the Python-optimised configurations to OPAL, and the constraints are still fulfilled.

          The optimiser
              is not optimised to find the first generation quickly. There
            is an optimizer flag called `INITIAL_OPTIMIZATION`, if you
            set this to TRUE (default FALSE), it will speed up the
          first generation. It is mostly for finding the last
          feasible individuals, so it will probably not help in your
          case.
        
      
    
    This sounds interesting. What does this option do, and what do you
    mean by "the last feasible individuals"?

          What you can also do is generate the feasible solutions with
          the surrogate model, make a JSON generation file from
          them, and start the optimisation with that generation (`STARTPOPULATION`).
      
    
    This is not possible because I'd like to calculate the speedup of
    ranning an optimisation with the surrogate model vs. with OPAL.

Hope that helps,

Jochem

This helps a lot, thank you!

Cheers,

Renato

---

From: opal-request AT lists.psi.ch <opal-request AT lists.psi.ch> on behalf of Renato Bellotti <renato.bellotti AT psi.ch>
Sent: Tuesday, May 5, 2020 4:10 PM
To: opal AT lists.psi.ch
Subject: [Opal] Optimiser

 

Dear OPAL developers,

I am experiencing problems with the optimiser. I am trying to solve the following problem:

You can see that I try to restrict the beam size within the first 10m of the accelerator.

Unfortunately, the optimiser does not find a single feasible individual, although it has tried > 7500 configurations.

I know that the problem has solutions that fulfil the constraint: Thanks to an ML surrogate model, I was able to run the optimisation with the pymoo Python library.

I am now a bit at a loss that OPAL cannot solve the problem while the Python library can. Am I doing something wrong in the config file (see appendix)?

I'm looking forward to your answers,

Renato