Decision variables

Decision variables
Fi,j	Flow in t/year of ammonia from node i to node j (defined for both Exporters to ports, and ports to importers)
xEx	Binary variable indicating if a supplier is active
xPo	Binary variable indicating if a new port has been built; can only be true if the exporter is designated as coastal
VPo	Volume (in m3) of tank storage required at a nominated port