- Relaxing the Irrevocability Requirement for Online Graph Algorithms.
- Joan Boyar, Lene M. Favrholdt, Michal Kotrbčík, and Kim S. Larsen.
In 15th International Algorithms and Data Structures Symposium (WADS), volume 10389 of Lecture Notes in Computer Science, pages 217-228. Springer, 2017.
Online graph problems are considered in models where the irrevocability
requirement is relaxed. Motivated by practical examples where, for
example, there is a cost associated with building a facility and no
extra cost associated with doing it later, we consider the
Late Accept model, where
a request can be accepted at a later point, but any acceptance is
irrevocable. Similarly, we also consider a Late Reject model, where an accepted
request can later be rejected, but any rejection is irrevocable (this
is sometimes called preemption).
Finally, we consider the Late Accept/Reject model,
where late accepts and rejects
are both allowed, but any late reject is irrevocable.
For Independent Set, the Late Accept/Reject model is
necessary to obtain a constant competitive ratio, but for Vertex
Cover the Late Accept model is sufficient and for Minimum Spanning Forest the
Late Reject model is sufficient.
The Matching problem has a competitive ratio of 2, but
in the Late Accept/Reject model, its competitive ratio is 3/2.
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