Document Type : Research Paper
Faculty of Industrial and Systems Engineering, Tarbiat Modares University, Tehran 1411713116, Iran
Background and Objectives: In this work, simultaneous production planning and scheduling in a real-world application, a production line of intravenous fluids and irrigation solutions at Darou Pakhsh Pharmaceutical Manufacturing Company is addressed.
Methods: A novel mixed-integer linear programming model is formulated for multi-period simultaneous production planning and scheduling. Since the problem is NP-hard in the strong sense, a memetic algorithm is proposed that reduces the computational effort of the problem. The chromosome representation is based on a permutation matrix, and a new algorithm is developed to construct a complete schedule from the permutation matrix through the planning horizon.
Results: 40 problems were investigated, containing 36 randomly generated instances and four real problems according to the data within the last two years. The generated instances were divided into small-sized, medium-sized, and large-sized instances. Among the 36 instances, 22 instances were optimally solved by both the exact method and the proposed memetic algorithm. The average gap for small-sized, medium-sized, and large-sized instances are respectively 0.00%, -1.15%, and -51.38%, indicating as the size of instances grows, the gap becomes considerable. The exact method could not reach an optimal solution for four real instances. The running time for real instances is expanded to 8 hours. The results revealed that the proposed memetic algorithm significantly outperformed the exact method in obtaining better solutions for real instances.
Conclusions: The computational results showed that the proposed memetic algorithm obtained optimal solutions on all the instances solved optimally by the exact method. It outperformed the exact method in other problems. This outperformance becomes more evident as the size of instances grows.