# how to create dummy vertices

Question asked by quarkinator on Jan 23, 2017
Latest reply on Jan 24, 2017 by Susanne.Heip

Hello,

I'm new to FICO XPRESS and I'm currently working on a vehicle routing problem with the possibility of refueling during the route. My problem concerns following constraint:

sum(for all j) x(ij) <= 1 for all i element of F'

According to this constraint, you can only visit a refueling station once, but it is possible to do that twice or third... route it would be optimal to visit the same refueling station as in the first route. So to distinguish the individual nodes to a refueling station it is necessary to introduce a unique node for each potential visit, let's say 10 potential visits.

F = the set of refueling stations --> in my example I have 2 refueling stations

F' = the set of dummy vertices generated to allow different visits to each node in the set of F refueling stations --> so 2 refueling stations * 10 potential visits = 20

My question is how can create this dummy set in XPRESS IVE? I have created the set of F refueling stations and given each an x and y coordinate.