“…In the temporal direction, unlike these finite difference schemes in [7,10,11], we develop a C 0 -continuous Galerkin linear finite element method to descritize the time derivatives (cf. [4,[12][13][14][15]). Since the approximate solution function is a continuous piecewise linear polynomial in the whole temporal interval, the regularity assumptions on the exact solution in the error analysis can be relaxed [4,16,17] (see Remark 1 in what follows).…”