Taillard's asymptotic tightness conjecture for permutation flowshop lower bounds

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Let MM be a fixed number of machines and let LB=max⁡{LBM+,LBJ}LB=\max\{LB_M^+,LB_J\}, where LBM+LB_M^+ and LBJLB_J are the machine-load and job-length lower bounds for the permutation flowshop scheduling problem, respectively. Let OPTOPT denote the optimal makespan, and interpret the probability over the processing-time instance distribution used for the problem.

Taillard's conjecture. For a fixed number of machines MM,

lim⁡N→∞P(LB=OPT)=1.\lim_{N\to\infty}\mathbb{P}(LB=OPT)=1.

The conjecture asserts that, as the number of jobs tends to infinity while the number of machines remains fixed, the lower bound LBLB is almost surely tight. Its resolution depends on the precise random-instance model for processing times, which is not specified in the supplied statement.

References

Primary source

J. A. Alejandro-Soto, Carlos Segura and Joel Antonio Trejo-Sanchez, “Bounds for the Permutation Flowshop Scheduling Problem: New Framework and Theoretical Insights”, arXiv:2509.23512 (2025).

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