Simple $k$-crashing Plan with a Good Approximation Ratio
<|reference_start|>Simple $k$-crashing Plan with a Good Approximation Ratio: In project management, a project is typically described as an activity-on-edge network (AOE network), where each activity / job is represented as an edge of some network $N$ (which is a DAG). Some jobs must be finished before others can be started, as described by the topology structure of $N$. It is known that job $j_i$ in normal speed would require $b_i$ days to be finished after it is started. Given the network $N$ with the associated edge lengths $b_1,\ldots,b_m$, the duration of the project is determined, which equals the length of the critical path (namely, the longest path) of $N$.   To speed up the project (i.e. reduce the duration), the manager can crash a few jobs (namely, reduce the length of the corresponding edges) by investing extra resources into that job. However, the time for completing $j_i$ has a lower bound due to technological limits -- it requires at least $a_i$ days to be completed. Moreover, it is expensive to buy resources. Given $N$ and an integer $k\geq 1$, the $k$-crashing problem asks the minimum amount of resources required to speed up the project by $k$ days. We show a simple and efficient algorithm with an approximation ratio $\frac{1}{1}+\ldots+\frac{1}{k}$ for this problem.   We also study a related problem called $k$-LIS, in which we are given a sequence $\omega$ of numbers and we aim to find $k$ disjoint increasing subsequence of $\omega$ with the largest total length. We show a $(1-\frac{1}{e})$-approximation algorithm which is simple and efficient.<|reference_end|>
@article{luo2024simple,
    title={Simple $k$-crashing Plan with a Good Approximation Ratio},
    author={Ruixi Luo and Kai Jin and Zelin Ye},
    journal={arXiv preprint arXiv:2404.10514},
    year={2024},
    archivePrefix={arXiv},
    eprint={2404.10514},
    primaryClass={cs.DS}
}