# Project Robust Scheduling Based on the Scattered Buffer Technology
## 1 Introduction  
Originally, project scheduling was carried out in a deterministic environment where all of the project environmental information is known and constant; however, in fact, a project environment is full of disruptions and risks from uncertainty. Therefore, the optimization scheme generated under the deterministic environment could produce large deviation from the expected one in its realized implementation, or it could even be infeasible. Robust project scheduling is an effective method to solve project scheduling problems under the uncertain environment; the goal is to produce a buffer scheduling that has high stability and has property of absorbing uncertain factors. This scheduling guides the project execution to ensure that all activities in the project start on time and the project is completed on schedule. Project robust scheduling reduces the frequency of rescheduling and the corresponding cost of the project. The uncertain parameters of the project environment include the activity duration, resources and scope and so on; among them, the uncertain duration is the most common. Currently, the robust scheduling of the uncertain duration has become an important research part in project scheduling. With the concept of resource flow network introduced into the research of robust scheduling, many scholars also pay attention to this research field. The application of the resource flow network has become an important method to study robust scheduling. The benefits of robust buffer scheduling generated under the resource flow network is to avoid the resource conflicts in the generation of thebuffer scheduling. At the same time, when the activity duration changes, the transitive relations of resources between activities will not be broken. If the transitive relations of resources are unchanged, no matter how the random activity duration will change, the precedence relations in the schedule and the feasibility of resources will not be affected. In recent years, studies on robust scheduling are quite rich. [PERSON] et al. added the quality parameter into the traditional time/cost trade-off problem to develop a time, cost, and quality trade-off problem (TCQTP) with some practical assumptions. Then, they integrated the TCQTP with a robust solution method to minimize the variation effect on time, cost, and quality to improve the robustness [1]. For the resource-constrained project scheduling problem with uncertain durations, the minimization of completion time of project is often taken as the objective function. The establishment of a robust optimization model to get the corresponding resource allocation scheme guarantees the robustness of the solution scheme [2; 3]. [PERSON] et al. used the Monte Carlo method to simulate the practical implementation of the project schedule task duration distribution, and evaluate the project schedule robustness by the probability of completing the project in the predicted duration [4]. At the same time, there are innovations in the study of this algorithm. [PERSON] and [PERSON] designed the two-stage hybrid algorithm based on EDA's multi-objective Markov network (MMEDA), and used local search procedure to balance two targets: the completion time and the robustness [5]. [PERSON] et al. designed a genetic algorithm based on the uncertainty simulation integrated A99 to find the approximate optimal scheduling [6]. [PERSON] et al. looked for the scheduling scheme that can minimize the completion time based on ant colony algorithm [7]. [PERSON] and [PERSON]\(\ddot{u}\)cha adopted parallel heuristic algorithm to solve the resource-constrained project scheduling problem with positive and negative time delay [8]. [PERSON] et al., [PERSON] and [PERSON] applied the critical chain/buffer management technology (CC/BM) to solve the resource conflict problem to balance the relationship between completion time and resources [9; 10].