“…To be more precise, in this paper, we will study the fractional diffusion equation described by the Grunwald-Letnikov derivative. For history, there exist many discussions related to the good definition of the fractional derivatives, and many papers were addressed in these directions, see [20,21]. Nowadays the most used fractional derivatives in fractional calculus are: Caputo-Liouville derivative [19], Liouville-Riemann derivative [19], conformable derivative, Grunwald-Letnikov derivative, Atangana-Baleanu derivative [22], Caputo-Fabrizio derivative [23].…”