[ library(gfd) | Reference Manual | Alphabetic Index ]
# disjunctive(+StartTimes, +Durations)

Constrain the tasks with specified start times and durations to not overlap in time.
*StartTimes*
- Collection of N start times for tasks (domain variables or integers)
*Durations*
- Collection of N durations for tasks (non-negative domain variables or integers)

## Description

A disjunctive scheduling constraint. StartTimes and Durations are
collections (a la collection_to_list/2) of equal size N of integer
variables or integers. Durations must be non-negative.

The declarative meaning is that the N tasks with the given start
times and durations do not overlap at any point in time, i.e. for
any pairs of tasks X and Y, the following holds:

(Xstart + Xduration =< Ystart) or (Ystart + Yduration =< Xstart)

Note that the constraint is implemented by different Gecode propagators,
depending on if Durations contains domain variables or not. If
Durations does have domain variables, the Gecode propagator requires
an extra End domain variable specifying the end time, and a constraint

End #= Start + Duration

for each task. These are posted as part of the constraint (the End
variables are not accessible by the user).
Any input variables which are not already domain variables will be
converted into domain variables with default bounds.

This constraint is also known as disjunctive in the global constraint
catalog, but in the catalog, tasks with zero duration are allowed
to overlap with other tasks. The constraint is implemented using
Gecode's unary constraint (with extra constraints on task end times if
any task duration is a domain variable).

## Examples

[eclipse 2]: disjunctive([1,7,4],[3,2,1]). % succeed
[eclipse 3]: disjunctive([1,7,3], [3,2,1]). % fail
[eclipse 4]: disjunctive([1,4,7,4],[3,0,2,1]). % succeed
[eclipse 5]: disjunctive([1,2,7,4],[3,0,2,1]). % fail
[eclipse 5]: [S2,S4]::[1..9], disjunctive([1,S2,7,S4], [3,1,2,1]).
S2 = S2{[4 .. 9]}
S4 = S4{[4 .. 9]}

## See Also

ic_edge_finder : disjunctive / 2, ic_edge_finder3 : disjunctive / 2, edge_finder : disjunctive / 2, edge_finder3 : disjunctive / 2, disjunctive_optional / 3, cumulative / 4, cumulatives / 5, eclipse_6 : collection_to_list / 2, lists : collection_to_list / 2