MATPOWER 2-bus test cases for OPF relaxations

This data set is composed of two test cases for optimal power flow (power flow optimisation in electrical networks). One test case "case2_parallel", shows a second-order cone relaxation gap when using the canonical branch flow model, but not when using the bus injection model. The other test case "case2_gap" shows a significant relaxation gap without total current constraints, and a much lower one with enforcement of total current limits.\nLineage: - The case2_parallel is a novel test case. \n- case2_gap was inspired by PowerModels.jl's "case5_gap" test case, itself available under BSD license.