[rules-users] Coarse Grained Moves

[DwProd .]

Hello there,

I'm pretty new to OptaPlanner, and I must say I'm really impressed with the
maturity of it all. Great software with a great documentation !

I've been working on a variation of the Cloud Balancing example, with a few
differences, which make it look like the Machine Reassignment problem as
well :

- Some processes are already placed and are immovable (using a Selection
Filter checking a boolean property of the planning entity)
- The Computer (the planning variable) is nullable (basically this is
Multiple Muti-Dimensional Knapsack problem) which means I added a soft
constraint penalty for processes with a null host.
- Processes can only be of a few classes (which I called services, a
Problem Fact). Processes of a given service type have a certain amount of
required cpu and ram.

Taking these elements into account, I do get very good results with
OptaPlanner. However, the following constraints always put me into a score
trap :

- For some services, processes work in groups. For instance, if groups are
of size 3, having 7 processes is not any better than having 6 processes. If
there were already 2 processes (immovable and placed), I should only add 4
processes and not 5, even if there are enough resources. For this
constraint, I have tried using a rule (medium constraint) accumulating
processes of that service and using the modulo operator with the group size.
- Some services are dependant on one another. For instance, I know that if
I have n1 groups of processes of the service 1, I require Math.ceil(2.5*n1)
groups of processes of the service 2. I have implemented this similarly
with a medium constraint...

With any (or both) of these constraints, little to no processes of the
concerned services are added and I fail to reach a good solution. I have
tried benchmarking with several local search methods and various
parameters, but all give the same results...

I feel like the next logical step would be to used the often mentioned in
the documentation "Coarse Grained Moves" but I fail to locate any simple
example. The Nurse Rostering example seems to use that technique to some
extent but it seems like an overly complicated example, is it not.

Thank you very much for reading this far, if you have any question,
guideline, or just a trick, I'd be absolutely delighted to hear from you !

Cheers,

Woody
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