In the GVF-Convex Solver calculation, the network is divided into multiple gravity and pressure sub-networks. In order to calculate each sub-network in correct order, the solver needs to find the upstream and downstream relationship between sub-networks. The following are the rules used in finding the upstream to downstream relationship between sub-networks:

• Flow direction is from upstream pressure pipe to downstream gravity node.
• Flow direction is from upstream conduit to a wet-well and then to downstream pressure sub-network.
• Flow direction is from diversion link start node gravity sub-network to stop node gravity sub-network, if the diversion link start node and stop node are not in the same gravity sub-networks