Abstract
We consider the clustered travelling salesman problem in which vertices ( except the starting vertex) of the network are divided into some prespecified clusters. The problem is to find a least cost Hamiltonian cycle (tour) in which vertices of any cluster are visited contiguously and the clusters are visited in the prespecified order. The problem is NP-hard and it arises in practical transportation and sequencing problems. This paper develops a lexisearch algorithm for obtaining exact optimal solution to the problem. The efficiency of the algorithm against an existing algorithm to the problem has been examined for asymmetric TSPLIB instances of various sizes and clusters. Finally, we present solutions to some symmetric TSPLIB instances.