“…By invoking the works in [37,43] and due to the nonlocality of time Caputo fractional derivatives which need high computational cost and storage, we can improve our approach in the near future by presenting a high-order scheme based on the sum of exponential functions technique to speed up the evaluation. Furthermore, recalling the methodologies in [37,44] side by side to the numerical analysis in [35] and the appropriate discrete Grönwall inequality in [35,45], the unconditional convergence and stability estimates with out any constraints on time and space steps can be deduced. Assuming that a 0 ≤ a(x 1 , x 2 ) ≤ a 1 and b 0 ≤ b(x 1 , x 2 ) ≤ b 1 , such that a 0 , b 0 and a 1 , b 1 are positive constants, is essential to prove the stability and convergence estimates which will be devoted to a new study in the near future.…”