“…We refer, for example, to the work of Diethelm and Ford ([10]) where the authors, by considering the equivalence of the problem with a Volterra integral equation, established sufficient conditions for the existence and uniqueness of the solution, and investigated the sensitivity of the solution to changes in the parameters of the problem, namely, in the initial value, in the order of the derivative and in the right-hand side function f . Concerning the numerical solution of (1.1)-(1.2) with a = 0 we refer, for instance, to the articles [6], [8], [12], [13], [15], [17] among many others.…”