Approximating discrete collections via local improvements
Proceedings of the sixth annual ACM-SIAM symposium on Discrete algorithms
Efficient web searching using temporal factors
Theoretical Computer Science
Approximate sequencing for variable length tasks
Theoretical Computer Science
On polynomial-time approximation algorithms for the variable length scheduling problem
Theoretical Computer Science
Matching Theory (North-Holland mathematics studies)
Matching Theory (North-Holland mathematics studies)
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The Variable Length Scheduling Problem has been studied in the context of web searching, where the execution time for a task depends on the start time for the task. The objective is to minimize the total completion time of all the tasks. It is known that the problem is NP-Hard to approximate within a factor of nO(1). For the case when the execution times are from the set {1, 2}, the optimal execution sequence can be determined in polynomial time. Also, when the execution times are from the set {k1, k2} the problem is NP-complete and can be approximated within a ratio of 2 + k2/2k1. Here we note that the approximation ratio for the case when the execution times are from the set {k1, k2} can be improved to 2 + 2k2/5k1.