Support for LP solvers

[Stazer]

Hi,

I added a feature for replacing the modified Edmonds-Karp algorithm with the usage of LP solvers like SCIP or IBM's CPLEX. Nevertheless, selecting other solvers like the modified Edmonds-Karp or Ford-Fulkerson is possible. Distributing 1000 users to 21 choices takes with SCIP (non-commercial solver) around 4 seconds and with CPLEX 3 seconds. LP solvers can be used on remote machines as well, either by using SSH or HTTP(S). All settings can be made by using moodles plugin settings form. The main purpose is for many ratingallocate instances, which run simultaneously and for moodle sites with high traffic, since the remote usage of LP solvers reduce web servers load.

Hopefully there is a use for it!

Best Regards

[tobiasreischmann]

Hey Stazer,
first of all, thanks for all the work you put in here and sorry that I did not reply for so long. However, I am not so sure if I want to take your code into the core of this plugin for two reasons. First, I do not see the necessity to solve the problems on external machines, since the algorithm runs usually as part of the cron, which does not have to be executed by the webserver, which serves the moodle site. Additional servers also increase the workload of maintenance.
Second, you produced lots of code, which I do not want to maintain in the future, since it generates additional workload for preparing future versions.
Nevertheless, I have a proposal for you. What do you think about a subplugin type for mod_ratingallocate, which allows to create own solvers and install them into the plugin. This subplugin type would offer an API, which allows for the development of different solvers such as the edmonds-karp algorithm or your lp solver. The subplugins would be stored in own repositories and could be linked in the readme. I hope this suggestion suits you.
We would need to discuss the interfaces of the subplugin API. Let me know, what you think.
Best regards,
Tobias