Originally posted by: SystemAdmin

[deborah said:]

Hi!

I would like to solve a scheduling problem using powerful OPL constructs. I have to schedule 'n' tasks between 'K' macchines.

I thought to declare:

-  the tasks as [i]interval [/i] variable, to define precedents constraint :

[center]dvar interval tasks[i in 1..n] size p[i];[/center]

- the machines as [i]sequence[/i] variable, becouse it represents a sequence of interval variables (tasks) :

[center]dvar sequence machines[k in 1..K] in all(i in 1..n) tasks[i];[/center]

I don't understand how I have to assign tasks to machines!!!

Thank you in advance.

Deborah


#DecisionOptimization
#OPLusingCPOptimizer

Originally posted by: SystemAdmin

[phlab said:]

Dear Deborah,
For modeling your problem in OPL/CPO, you will have to create one optional interval variable [tt]tasksOnMachine[i ][k][/tt] for each possible allocation of a given task i to one of the 'K' machines. And then, you will create an alternative constraint between [tt]task[i ][/tt] and all possible allocations [tt]tasksOnMachine[i ][k][/tt] of this task i on the K machines.

The OPL formulation looks like this:


dvar interval tasks[i in 1..n] size p;
dvar interval tasksOnMachines[i in 1..n][k in 1..K] optional;
dvar sequence machines[k in 1..K] in all(i in 1..n) tasksOnMachines[i][k];

constraints {
  forall(i in 1..n)
    alternative(tasks[i], all(k in 1..K) tasksOnMachines[i][k]);
  forall(k in 1..K)
    noOverlap(machines[k]);
};


Hope it helps,

Philippe
#DecisionOptimization
#OPLusingCPOptimizer

Originally posted by: SystemAdmin

[deborah said:]

Dear Philippe,

thank you very very much. Your response has been very useful!!

Deborah
#DecisionOptimization
#OPLusingCPOptimizer