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Encodings
Several encoding and associated utilities are provided in the jobshop.encodings package.
The abstract class Encoding provides a common interface for all encodings.
The only requirement for an encoding is to be able to transform itself into a Schedule.
The jobshop.encodings package contains a Task class that allows representing a particular task of a jobshop instance.
A Task object contains a pair of integers (job, task) that respectively specify the job in which the task appears, and the index of the task in this job.
For instance the task created with new Task(0, 2) would represent the third task of the first job.
Schedule
The Schedule is direct encoding of a solution: it associates every task in the jobshop instance to a start time.
It plays a particular role as it is the standard way of representing a solution. As a consequence, all other encodings must provide a way to produce a schedule.
Convenience methods:
isValid(): returns true if the schedule is valid (no violated constraints).makespan(): computes the makespan of the solution.criticalPath(): returns a critical path in the solution.asciiGantt(): generates a Gantt chart view of the solution in ASCII art.
JobNumbers
The JobNumbers encoding consists of a sequence of job numbers. To produce a schedule, one should iterate on the job numbers and try to schedule as early as possible the next task of the job.
For instance the encoding [0 0 1 1 0 1] will produce a schedule by trying to place as early as possible the following tasks (in this order):
(0, 0): first task of the first job(0, 1): second task of the first job(1, 0): first task of the second job(1, 1): second task of the second job(0, 2): third task of the first job(1, 2): third task of the second job
ResourceOrder
The resource order encoding specifies the order in which each machine will process its tasks.
Each machine is associated with an array of tasks that specifies the order on which the tasks must be scheduled on the machine.
For instance, the (completely fictional) encoding:
machine 0: [(0, 1), (1, 0)]
machine 1: [(0, 0), (1, 1)]
machine 2: [(1, 2), (0, 2)]
specifies that the first machine (machine 0) will first process the second task of the first job (0, 1) and only when it is finished can start processing the first task of the second job (1, 0).
Unlike JobNumbers, the ResourceOrder encoding might represent invalid solutions. In this case, its toSchedule() method will return an empty result.