Flux cone projection. (A): A small metabolic network. The reactions in the interesting subnetwork are shown as thick arrows. (B): The flux cone of this network, shown in light gray, can be generated by vectors g1 and g2. The projected cone is shown in dark gray. The projected cone can be generated by g1 and g3 in a 2D plane. (C): the same metabolic network as in A, but with reaction 3 removed. The flux cone of this network is generated by only one vector, namely g1.