Node-arc incidence matrix
For the minimum-cost network-flow problem, this is a matrix in which the rows i correspond to the nodes and the columns j correspond to the arcs. For an arc (i, j), with its flow directed from i to j, the entry in matrix location (i, j)is a + 1 and the entry in location (j, i)is a − 1. All other entries are zero. Thus, every column has only two nonzero entries. Such matrices are unimodular. Minimum-cost network-flow problem; Multicommodity network flows; Network optimization.