Linear connections on graphs

In recent years, discrete spaces such as graphs have attracted much attention as models for physical spacetime or as models for testing the spirit of noncommutative geometry. In this work, we construct the differential algebras for graphs by extending the work of Dimakis et al. and discuss linear connections and curvatures on graphs. Especially, we calculate connections and curvatures explicitly for the general nonzero torsion case. There is a metric, but no metric-compatible connection in general except the complete symmetric graph with two vertices.