![](bg7.png)
stances solved to optimality, the number of instances
for which the model found a solution and the number
of instances to solve for this combination.
Note that a company that solves this problem will
just have to generate all the valid routes once for each
set of customers considered, and what will change in
practice are the demands.
5 CONCLUSIONS
The multi-trip inventory routing problem has a great
practical interest in the industrial field, but on the
other hand, it is quite challenging in terms of reso-
lution.
In this paper, we propose a network flow model for
multi-trip inventory routing problem, which is solved
exactly for a set of adapted instances in the literature.
The model was able to solve instances up to 50 cus-
tomers and 15 time periods in reasonable computa-
tional times. Several instances were solved to opti-
mality when set to different parameters. The average
gap obtained was relatively low.
ACKNOWLEDGEMENTS
This work was supported by FEDER funding through
the Programa Operacional Factores de Competitivi-
dade - COMPETE and by national funding through
the Portuguese Science and Technology Founda-
tion (FCT) in the scope of the project PTDC/EGE-
GES/116676/2010.
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