Indicator

The Indicator class allows to define a criterion that quantifies the schedule so that it can be compared with other schedules. An Indicator measures a specific behaviour you need to trace, evaluate or optimize.

All builtin indicators inherit from the base class Indicator:

classDiagram
  Indicator
class Indicator{
    +List[int, int] bounds
  }

Indicator values are computed by the solver, and are part of the solution. If the solution is rendered as a matplotlib Gantt chart, the indicator value is displayed on the upper right corner of the chart.

Note

There is no limit to the number of Indicators defined in the problem. The mathematical expression must be expressed in a polynomial form and using the Sqrt function. Any other advanced mathematical functions such as exp, sin, etc. is not allowed because not supported by the solver.

Builtin indicators

Available builtin indicators are listed below:

Type	Apply to	Description
IndicatorTardiness	List of tasks	Unweighted total tardiness of the selected tasks
IndicatorEarliness	List of tasks	Unweighted total earliness of the selected tasks
IndicatorNumberOfTardyTasks	List of tasks	Number of tardy tasks from the selected tasks
IndicatorMaximumLateness	List of tasks	Maximum lateness of selected tasks
IndicatorResourceUtilization	Single resource	Resource utilization, from 0% to 100% of the schedule horizon, of the selected resource
IndicatorResourceIdle	Single resource	Resource idle, i.e. total time waiting for the next job to be processed
IndicatorNumberTasksAssigned	Single resource	Number of tasks assigned to the selected resource
IndicatorResourceCost	List of resources	Total cost of selected resources
IndicatorMaxBufferLevel	Buffer	Maximum level of the selected buffer
IndicatorMinBufferLevel	Buffer	Minimum level of the selected buffer

Customized indicators

Use the IndicatorFromMathExpression class to define an indicator that may not be available from the previous list.

ind = ps.IndicatorFromMathExpression(name="Task1End",
                                     expression=task_1._end)

or

ind = ps.IndicatorFromMathExpression(name="SquareDistanceBetweenTasks",
                                     expression=(task_1._start - task_2._end) ** 2)

Customized indicators can also be bounded, although it is an optional feature. Bounds are constraints over an indicator value. It is useful if the indicator is further be maximized (or minimized) by an optimization solver, in order to reduce the computation time. For example,

indicator1 = Indicator(name='Example1',
                       expression=task2.start - task1.end,
                       bounds = (0,100)) # If lower and upper bounded
indicator2 = Indicator(name='Example2',
                       expression=task3.start - task2.end,
                       bounds = (None,100)) # If only upper bounded
indicator3 = Indicator(name='Example3',
                       expression=task4.start - task3.end,
                       bounds = (0,None)) # If only lower bounded

Bounds are set to None by default.