Goyannes Gusmão Caiado, R.; Caetano Heymann, M.; Luis Rey da Silveira, C. .; Angulo Meza, L. .; Gonçalves Quelhas, O. L. Measuring the Eco-Efficiency of Brazilian Energy Companies Using DEA and Directional Distance Function. IEEE LAT AM T 2021, 18, 1844-1852.