Retrieves the 'duration' variable of a task.
A cptask is represented by three cpvar:

• 'start' representing the start time of the task
• 'end' representing the completion time of the task
• 'duration' representing the duration of the task.

These three structural variables are linked with the following constraint: start + duration ≤ end.
The duration variable represents two specific parameters of the task: the minimum task duration (Dmin, represented by its lower bound) and the maximum task duration (Dmax represented by its upper bound). The graphic below illustrates these properties:

The cpvar representing the duration of t

getstart getend getconsumption getrequirement getproduction getprovision