Coloring application Branching Rule contradictory code

[meffertj]

Hello,

The coloring branch and price application documentation says it selects the "most" fractional variable (both in the doc and in the branch_coloring.c itself) but in the actual code it selects the "least" fractional variable, even stating so in the comment:

https://github.com/scipopt/scip/blob/6d9a5d4b96030945e8f620bf03887a59e0bd31a9/applications/Coloring/src/branch_coloring.c#L141

[meffertj]

I could do a pull request editing the mentioned code segment to indeed select the most fractional node

[ambros-gleixner]

Yes, that would be wonderful. Thank you for noticing!

If you wanted to then you could even introduce a parameter to be able to switch between most and least fractional. But I believe that least fractional leads to better performance in practice.

[meffertj]

Alright, I changed the section in my fork. https://github.com/meffertj/scip_vcp_mostfractional/blob/master/applications/Coloring/src/branch_coloring.c

Do you have a recommendation as to what the most elegant place to introduce that parameter would be?

[ambros-gleixner]

Yes, the include method of the branching rule would be the natural place to do so, see https://github.com/meffertj/scip_vcp_mostfractional/blob/master/src/scip/branch_pscost.c#L777 for one example.

[ambros-gleixner]

A character parameter from the string "ml" might be a natural choice.

[leoneifler]

Is there any progress on this?

[meffertj]

I‘ve implemented it. My windows machine died, have since been working on my mac and was not able to test it yet

[meffertj]

I've fixed one error, now all tests run successfully - correctly solving when selecting the strategy via {m,l} and exiting with error message when not passing one of ml. I am not sure if it is justified to add myself as an author to the file, depending on your approval I can do a pull request

[ambros-gleixner]

Great, thank you very much! It is absolutely good to add you as an author. I have transferred your branch to the internal repo where we merge and run the CI. @GioniMexi will be in contact with you regarding this!

[ambros-gleixner]

Your code has been merged and should be available on the master branch now. Can you confirm and close the comment if all looks good? Thank you again for your contribution!

[meffertj]

Looks good, thank you!