The traveling salesman problem is one of the most important problems in operations
research, especially when additional precedence constraints are considered. Here, we
consider the well-known variant where a linear order on k special vertices is given
that has to be preserved in any feasible Hamiltonian cycle. This problem is called Ordered
TSP and we consider it on input instances where the edge-cost function satisfies a
β-relaxed
triangle inequality, i.e., where the length of a direct edge cannot
exceed the cost of any detour via a third vertex by more than a factor of
β> 1. We
design two new polynomial-time approximation algorithms for this problem. The first
algorithm essentially improves over the best previously known algorithm for almost all
values of k
and β<
1.087889. The second algorithm gives a further improvement for
2n ≥ 11k +
7 and β< √34/3 , where n is the number of vertices in the graph.