“…Several complex phenomena can be modeled with the help of using these equations [10,11]. As a result, many applications of these equations can be found in the study of viscoelasticity, electrochemistry, signal processing, control theory, porous media, fluid mechanics, rheology, transport by diffusion, electrical networks, electromagnetic, probability distributions, and many other processes [5,6,12]. In fact, the existence and uniqueness results of the weak solutions were widely investigated for several fractional-order partial differential equations using Lax Milgram theorem, see [13,14] and the references therein.…”