Tavares, DinaAlmeida, RicardoTorres, Delfim F. M.2018-06-282018-06-282017-04-210377-0427http://hdl.handle.net/10400.8/3309We study two generalizations of fractional variational problems by considering higher-order derivatives and a state time delay. We prove a higher-order integration by parts formula involving a Caputo fractional derivative of variable order and we establish several necessary optimality conditions for functionals containing a combined Caputo derivative of variable fractional order. Because the endpoint is considered to be free, we also deduce associated transversality conditions. In the end, we consider functionals with a time delay and deduce corresponding optimality conditions. Some examples are given to illustrate the new results. Computational aspects are discussed using the open source software package Chebfun.engFractional calculus of variationsVariable fractional orderHigh-order derivativesTime delayComputational approximationjournal article10.1016/j.cam.2017.04.042