Electronic Journal of Differential Equations, Vol. 2020 (2020), No. 120, pp. 1–10. ISSN: 1072-6691. URL: http://ejde.math.txstate.edu or http://ejde.math.unt.edu ROTHE’S METHOD FOR SOLVING SEMI-LINEAR DIFFERENTIAL EQUATIONS WITH DEVIATING ARGUMENTS DARSHANA DEVI, DURANTA CHUTIA, RAJIB HALOI Abstract. We consider a semi-linear differential equation of parabolic type with deviating arguments in a Banach space with uniformly convex dual, and apply Rothe’s method to establish the existence and uniqueness of a strong solution. We also include an example as an application of the main result. 1. Introduction In differential equations with deviating arguments the unknown function and its derivative are evaluated at different values of their arguments. They are consid- ered as one of the most important and frequently used differential equations and hence the study of these equations has been rapidly increasing. They are widely used in various branches of science and technology such as self-oscillating systems, automatic control, problems related with combustion in rocket motion, long-term planning in economics, biological problems, and many other areas of science and technology [11, 13]. The very familiar hot shower problem is closely related to these differential equations. For an extensive reading on differential equations with deviating arguments, we refer the reader to [8, 9, 10, 12, 14, 17]. Rothe’s method was introduced by Rothe [25] in 1930 to solve a scalar parabolic initial value problem of second order. Rothe used time discretization to develop his method so the method is also known as the method of semidiscretization or the method of lines. Later on many authors have used and developed this method, see [1, 2, 5, 7, 16, 24]. Rothe’s method is effectively used to establish the existence and uniqueness of solution of equations such as linear, nonlinear, parabolic and hyperbolic equations with higher orders. The method is also used to study the diffusion problems [6, 18, 20, 22, 23]. Recently Rothe’s method is also applied to study variational-hemivariational inequalities with applications to contact mechan- ics [3, 4, 19],. Thus the application of this method is not limited to mathematics but also applicable to physics and biology. The method becomes a strong and efficient tool to analyze the existence and uniqueness of solution to differential equations. 2010 Mathematics Subject Classification. 34G20, 34K30, 35D35, 35K58. Key words and phrases. Strong solution; deviating argument; semigroup of bounded linear operators; semidiscretization method. c©2020 Texas State University. Submitted October 23, 2020. Published December 10, 2020. 1 2 D. DEVI, D. CHUTIA, R. HALOI EJDE-2020/120 Raheem and Bahuguna [23] applied Rothe’s method to study the fractional in- tegral diffusion equation in a Banach space X, ∂u(t) ∂t +Au(t) = 1 Γ(α) ∫ t 0 u(s) (t− s)1−α ds+ f(t), t ∈ (0, T ], u(0) = u0, where 0 < α < 1, -A is the infinitesimal generator of a C0-semigroup of contractions, f is a given map from [0, T ] to X, and the initial point u0 ∈ D(A) ⊂ X, the domain of A. Dubey [7] used the method for the nonlinear nonlocal functional differential equation in a Banach space X, u′(t) +Au(t) = f(t, u(t), ut), t ∈ (0, T ], h(u0) = φ on [−τ, 0], where 0 < T < ∞, φ ∈ C0 := C([−τ, 0];X), τ > 0, the nonlinear operator A is single-valued and m-accretive defined from the domain D(A) ⊂ X to X, the nonlinear map f is defined from [0, T ]×X×C0 to X, the map h is defined from C0 to C0. For u ∈ CT := C([−τ, T ];X), the map ut ∈ C0 is defined by ut(s) = u(t+ s) for s ∈ [−τ, 0]. Here, Ct := C([−τ, t];X) for t ∈ [0, T ] is the Banach space of all continuous functions from [−τ, t] into X endowed with the supremum norm, ‖φ‖t = sup τ≤η≤t ‖φ(η)‖, φ ∈ Ct, where ‖ · ‖ is the norm in X. In this article, we consider the following semi-linear differential equation with deviating arguments. Let (X, ‖·‖) be a Banach space with a uniformly convex dual X∗. ∂u(t) ∂t +Au(t) = f(t, u(t), u(h(u(t), t))), t ∈ (0, T ], u(0) = u0, u0 ∈ X. (1.1) We assume that for each t ∈ (0, T ], −A is the infinitesimal generator of a C0- semigroup of contractions, the non-linear continuous maps f : [0, T ]×X ×X → X and h : X×[0, T ]→ [0, T ] satisfy suitable growth conditions in its arguments stated in next section. 2. Preliminaries and main result In this section we briefly state some definitions and results need for proving the main result. At the end of this section, we state our main result. Definition 2.1. Let X be a Banach space and X∗ be its dual. For every x ∈ X we define the duality map P as P (x) = {x∗ ∈ X∗ : (x∗, x) = ‖x‖2 = ‖x∗‖2}, where (x∗, x) denotes the value of x∗ at x. Definition 2.2. A nonlinear operator A : D(A) ⊂ X → X is called m-accretive if (i) (Ax−Ay, P (x− y)) ≥ 0, for all x, y ∈ D(A), (ii) R(I +A) = X, where R(·) is the range of an operator. Lemma 2.3 ([21, Theorem 1.4.3]). If -A is the infinitesimal generator of a C0 semigroup of contractions, then A is m-accretive, i.e., EJDE-2020/120 ROTHE’S METHOD WITH DEVIATING ARGUMENTS 3 (i) (Au−Av, P (u− v)) ≥ 0, for all u, v ∈ D(A), where P is the duality map. (ii) For each λ > 0, we have R(I + λA) = X, where I is the identity operator on X and R(·) denotes range of an operator. Lemma 2.4 ([15, Lemma 2.5]). Let X be a Banach space and X∗ be its uniformly convex dual. Let -A be the infinitesimal generator of a C0 semigroup of contractions. Consider the sequence Xn ∈ D(A), n = 1, 2, 3, . . . such that Xn → u ∈ X and if ‖AXn‖ are bounded, then u ∈ D(A) and AXn ⇀ Au. Lemma 2.5 ([23]). Let α1, α2, . . . , αj be non-negative numbers satisfying (i) α1 ≤ B, (ii) αi ≤ B + Cλ ∑i−1 k=1 αk, where B, C and λ are positive constants. Then for each i = 1, 2, . . . , j we have αi ≤ BeC(i−1)λ. We use the following assumptions for proving our main result. (A1) Suppose there exists a constant Lf > 0 such that for each x, y, x′, y′ ∈ X and t, s ∈ [0, T ], the function f : [0, T ]×X ×X → X satisfies ‖f(t, x, x′)− f(s, y, y′)‖ ≤ Lf (|t− s|+ ‖x− y‖+ ‖x′ − y′‖). (A2) Let there exists a constant L1 > 0 such that for each x, y ∈ X and t, s ∈ [0, T ] the map h : X × [0, T ]→ [0, T ] satisfies |h(x, t)− h(y, s)| ≤ L1(‖x− y‖+ |t− s|). Remark 2.6. For each x, y ∈ X and t, s ∈ [0, T ], we have ‖x(h(x, t))− y(h(y, s))‖ ≤ L2(|h(x, t)− h(y, s)|) ≤ L2[L1(‖x− y‖+ |t− s|)] = Lh(‖x− y‖+ |t− s|), for some constants L1, L2, Lh > 0. Theorem 2.7. Let (A1) and (A2) be satisfied. Then the initial value problem (1.1) has a unique strong solution u on the interval [0, T ]. More precisely we have, u ∈ C([0, T ];X) such that u(t) ∈ D(A), u is differentiable a.e. on [0, T ] and u satisfies (1.1). 3. Approximation In this section, we use time discretization to approximate the system (1.1) by corresponding parabolic problems and construct an approximate solution to the original problem. Also we prove the convergence of this approximate solution to the solution of (1.1) with the help of analogues results for the approximate equations of the original system. To apply the Rothe’s Method, we consider the interval [0, T ] and divide it into the subintervals of length λn = T n . We use the following approximate equations to replace the system (1.1). For i = 1, we have un1 − un0 λn +Aun1 = f0, un0 = u0, (3.1) and for 2 ≤ i ≤ n, we use the equations, uni − uni−1 λn +Auni = fni−1, (3.2) 4 D. DEVI, D. CHUTIA, R. HALOI EJDE-2020/120 where, fni = f(tni , u n i , u ′n i ), uni = u(tni ), u′ n i = u(h(uni , t n i )), and f0 = fn(0, u0, u(h(u0, 0))). Next we successively establish the existence and uniqueness of solution of the approximate equations un1 − un0 λn +Aun1 = f0, un0 = u0, (3.3) uni − uni−1 λn +Auni = fni−1, i = 2, 3, . . . , n. (3.4) The existence of a unique solution uni ∈ D(A) to the system (3.2) is a consequence of Lemma 2.3. We now define the Rothe’s sequence as Un(t) = { u0, if t = 0, uni−1 + 1 λn (t− tni−1)(uni − uni−1), if t ∈ (tni−1, t n i ]. Before proving the main result, we now present some results which are needed. Lemma 3.1. For each n ∈ N and i = 1, 2, . . . , n, the estimate ‖uni ‖ ≤ C holds for some constant C > 0 and the constant is independent of n, i and λn. Proof. From (3.3), we have un1 + λnAu n 1 = un0 + λnf0. Applying P (un1 ) on both sides and using the definition of accretivity of A, we obtain ‖un1‖ ≤ ‖un0‖+ λn‖f0‖ ≤ ‖u0‖+ T‖f0‖ = C1(say). From (3.4) and for 2 ≤ i ≤ n, we have uni + λnAu n i = uni−1 + λnf n i−1. We apply P (uni ) on both sides and use the definition of accretivity of A to obtain ‖uni ‖ ≤ ‖uni−1‖+ λn‖fni−1‖. By using the hypotheses (A1) and (A2) in the above equation, we obtain ‖uni ‖ ≤ ‖uni−1‖+ λn [ Lf { |tni−1|+ ‖uni−1 − u0‖+ Lh ( ‖uni−1 − u0‖+ |tni−1| )} + ‖f0‖ ] = ‖uni−1‖+ λn [ Lf |tni−1|(1 + Lh) + ‖f0‖ ] + λnLf‖uni−1 − u0‖(1 + Lh). Repeating above process, we obtain ‖uni ‖ ≤ ‖u0‖+ iλn [ Lf |tni−1|(1 + Lh) + ‖f0‖ ] + iλnLf‖u0‖(1 + Lh) + λnLf (1 + Lh) i−1∑ j=1 ‖unj ‖ ≤ ‖u0‖ { 1 + TLf (1 + Lh) } + T { LfT (1 + Lh) + ‖f0‖ } + λnLf (1 + Lh) i−1∑ j=1 ‖unj ‖. EJDE-2020/120 ROTHE’S METHOD WITH DEVIATING ARGUMENTS 5 Applying Lemma 2.5 on the above inequality, we obtain ‖uni ‖ ≤ [ ‖u0‖ { 1 + TLf (1 + Lh) } + T { LfT (1 + Lh) + ‖f0‖ }] eLf (1+Lh)(i−1)λn ≤ [ ‖u0‖ { 1 + TLf (1 + Lh) } + T { LfT (1 + Lh) + ‖f0‖ }] eLf (1+Lh)T = C. This completes the proof. � Lemma 3.2. For each n ∈ N and i = 1, 2, . . . , n there exists a positive constant C which is independent of n, i and λn such that ‖ uni − uni−1 λn ‖ ≤ C. Proof. From (3.3), we obtain un1 − u0 λn +Aun1 −Au0 = f0 −Au0. Applying P (un1 − u0) on the above equation and using the definition of accretivity of A, we obtain ‖u n 1 − u0 λn ‖ ≤ ‖f0‖+ ‖Au0‖ = C1(say). (3.5) We rewrite the equation (3.4) for the index i− 1 and subtract it from (3.4), we obtain uni − uni−1 λn +Auni −Auni−1 = uni−1 − uni−2 λn + fni−1 − fni−2. Again we apply P (uni − uni−1) on both sides to deduce the following estimates∥∥uni − uni−1 λn ∥∥ ≤ ∥∥uni−1 − uni−2 λn ∥∥+ ‖fni−1 − fni−2‖ ≤ ∥∥uni−1 − uni−2 λn ∥∥+ Lf { |tni−1 − tni−2|+ ‖uni−1 − uni−2‖ + Lh ( ‖uni−1 − uni−2‖+ |tni−1 − tni−2| )} = ∥∥uni−1 − uni−2 λn ∥∥+ Lf (1 + Lh)|tni−1 − tni−2|+ Lf (1 + Lh)λn ∥∥uni−1 − uni−2 λn ∥∥ = Lf (1 + Lh)λn + { 1 + Lf (1 + Lh)λn }∥∥uni−1 − uni−2 λn ∥∥ . We put C2 = Lf (1 + Lh) and repeating the above inequality, we obtain∥∥uni − uni−1 λn ∥∥ ≤ K + (1 + C2λn)i−1 ∥∥un1 − u0 λn ∥∥, (3.6) where, K = C2λn { 1 + (1 + C2λn) + (1 + C2λn)2 + · · ·+ (1 + C2λn)i−2 } = (1 + C2λn)i−1 − 1. Now, we have (1 + C2λn)i−1 ≤ eC2λn(i−1) ≤ eC2T . 6 D. DEVI, D. CHUTIA, R. HALOI EJDE-2020/120 Hence K is a constant independent of n, i and λn. Thus from the estimates (3.5) and (3.6), we obtain ∥∥uni − uni−1 λn ∥∥ ≤ K + eC2TC1 = C. This completes the proof. � Next we define a sequence of step functions Y n(t) = { u0 if t = 0, uni if t ∈ (tni−1, t n i ]. Remark 3.3. From Lemma 3.2, we can conclude that Un(t) is uniformly Lipschitz continuous and Un(t)− Y n(t)→ 0 as n→∞. We define fn(t) = f(tni , u n i , u ′n i ). Then equation (3.3) and (3.4) can be rewritten as d dt Un(t) +AY n(t) = fn(t), t ∈ (0, T ]. (3.7) where d dt denotes the left derivative in the interval (0, T ]. For t ∈ (0, T ], we have∫ t 0 AY n(s)ds = u0 − Un(t) + ∫ t 0 fn(s)ds. (3.8) Lemma 3.4. There exists u ∈ C([0, T ];X) such that Un → u in C([0, T ];X) as n→∞. Moreover, u is Lipschitz continuous on [0, T ]. Proof. From (3.7), we see that d dt Un(t)− d dt Um(t) +AY n(t)−AY m(t) = fn(t)− fm(t). Applying P (Y n(t)− Y m(t)), using the definition of accretivity of A, we obtain ( d dt Un(t)− d dt Um(t), P (Y n(t)− Y m(t)) ≤ (fn(t)− fm(t), P (Y n(t)− Y m(t)). From the above inequality and using that ( d dt Un(t)− d dt Um(t), P (Un(t)− Um(t)) = 1 2 d dt ∥∥Un(t)− Um(t) ∥∥2, we obtain ( d dt Un(t)− d dt Um(t), P (Un(t)− Um(t)) ≤ (fn(t)− fm(t), P (Y n(t)− Y m(t)) + ( d dt Un(t)− d dt Um(t), P (Un(t)− Um(t)) − ( d dt Un(t)− d dt Um(t), P (Y n(t)− Y m(t)) = ∥∥ d dt (Un(t)− Um(t) ∥∥(‖Un(t)− Um(t)‖ − ‖Y n(t)− Y m(t)‖ ) + ‖fn(t)− fm(t)‖‖Y n(t)− Y m(t)‖ ≤ ∥∥ d dt (Un(t)− Um(t) ∥∥(‖Un(t)− Um(t)− Y n(t) + Y m(t)‖ ) + ‖fn(t)− fm(t)‖‖Y n(t)− Y m(t)‖. EJDE-2020/120 ROTHE’S METHOD WITH DEVIATING ARGUMENTS 7 which implies 1 2 d dt ∥∥Un(t)− Um(t) ∥∥2 ≤ ∥∥ d dt (Un(t)− Um(t) ∥∥(‖Un(t)− Y n(t)‖+ ‖Um(t)− Y m(t)‖ ) + Lf { |tni − tmi |+ ‖uni − umi ‖+ Lh(‖uni − umi ‖+ |tni − tmi |) } ‖Y n(t)− Y m(t)‖ which implies d dt ∥∥Un(t)− Um(t) ∥∥2 ≤ σ1 nm(t) (say), and σ1 nm(t)→ 0 as n,m→∞. This implies ‖Un(t)− Um(t)‖2 ≤ σ2 nm(t), where σ2 nm(t) = ∫ t 0 σ1 nm(s)ds and σ2 nm(t)→ 0 as n,m→∞. Taking the supremum, we obtain sup tε(0,T ] ‖Un(t)− Um(t)‖2 ≤ σ2 nm(t). Using the above inequality, we conclude that Un → u in C([0, T ], X). Since each Un is uniformly Lipschitz continuous, it follows that u is Lipschitz continuous. � Remark 3.5. As the sequence Un(t) − Y n(t) → 0 as n → ∞, Y n(t) → u(t). Furthermore it is clear that Y n(t) ∈ D(A) for each n ∈ N. Also ‖AY n‖ are bounded so by Lemma 2.4, we can conclude that AY n ⇀ Au. Proof of Theorem 2.7. For every x∗ ∈ X∗ and t ∈ (0, T ], we have∫ t 0 (AY n(s), x∗)ds = (u0, x ∗)− (Un(t), x∗) + ∫ t 0 (fn(s), x∗)ds. (3.9) From the Lemma 3.4, Remark 3.5 and the bounded convergence theorem, from (3.9) after considering the limit as n→∞, we obtain∫ t 0 (Au(s), x∗)ds = (u0, x ∗)−(u(t), x∗)+ ∫ t 0 (f(s, u(s), u(h(u(s), s))), x∗)ds. (3.10) Since Au(t) is Bochner integrable on [0, T ], from equation (3.10), we obtain d dt u(t) +Au(t) = f(t, u(t), u(h(u(t), t))) a.e. t ∈ (0, T ]. (3.11) Now it is clear that u ∈ C([0, T ];X) and differentiable on (0, T ] with u(t) ∈ D(A); u(0) = u0 and satisfies the problem (3.11). Therefore it will be a strong solution of the problem (1.1) on [0, T ]. Next we prove the uniqueness of the solution. For this, if possible we assume that u1 and u2 are two strong solutions of (1.1). We put u = u1 − u2, from (3.11), we have ( du(t) dt , P (u(t))) + (Au(t), P (u(t))) = (f(t, u1(t), u(h(u1(t), t))− f(t, u2(t), u(h(u2(t), t)), P (u(t))). 8 D. DEVI, D. CHUTIA, R. HALOI EJDE-2020/120 By using the definition of accretivity of A, we obtain(du(t) dt , P (u(t)) ) ≤ (f(t, u1(t), u1(h(u1(t), t))− f(t, u2(t), u2(h(u2(t), t)), P (u(t))). We used that (du(t) dt , P (u(t)) ) = 1 2 d dt ‖u(t)‖2. From an easy calculation we obtain d dt ‖u(t)‖2 ≤ C‖u(t)‖2 a.e. t ∈ (0, T ], where C = 2Lf (1 + Lh). Integrating over the interval (0, t), we obtain ‖u(t)‖2 ≤ C ∫ t 0 ‖u(s)‖2ds. Applying Gronwall’s inequality, we obtain u = 0 on [0, T ]. This shows the unique- ness of the strong solution and hence it completes the proof. � 4. Application We consider the equation with deviating argument, ∂u(t, x) ∂t + ∂2u(t, x) ∂x2 = F (x, u(t, x)) +G(t, x, u(t, x)), u(t, 0) = u(t, 1), 0 < t ≤ T, u(0, x) = u0(x), x ∈ Ω. (4.1) where Ω is a bounded domain in Rn. Here F (x, u(t, x)) = ∫ x 0 ξ(x, y)u(f(t)|u(t, y)|, y)dy ∀(t, x) ∈ (0, T ]× Ω. We assume that f : [0, T ]→ R+ is locally Hölder continuous in t with f(0) = 0; ξ ∈ C1(Ω × Ω;R); the function G : [0, T ] × Ω × R → R is measurable in x, locally Hölder continuous in t, locally Lipschitz continuous in u and uniformly continuous in x. Let X = L2(Ω;R). We define X1 = D(A) = H2(Ω) ∩ H1 0 (Ω) and Au = ∂2u ∂x2 . Then X1/2 = D((A)1/2) = H1 0 (Ω). For x ∈ Ω, we define the map f : [0, T ]×H2(Ω)× L2(Ω)→ H1 0 (Ω) by g(t, φ, ψ) = F (x, ψ) +G(t, x, φ), where F (x, ψ(x, t)) = ∫ x 0 ξ(x, y)ψ(y, t)dy. We also assume that the map G : [0, T ]× Ω×H2(Ω)→ H0 1 (Ω) that a C > 0, ‖G(t, x, u)−G(r, x, w)‖ ≤ C(|t− r|+ ‖u− v‖). Thus, the map g satisfies assumption (A1) (see [9]) and h : H2(Ω) × [0, T ] → R+ defined by h(φ(x, t), t) = f(t)|φ(x, t)| satisfies assumption (A2) (see [9]). Then problem (4.1) reduces to the system ∂u(t) ∂t +Au(t) = f(t, u(t), u(h(u(t), t))), t ∈ (0, T ], u(0) = u0, u0 ∈ X, EJDE-2020/120 ROTHE’S METHOD WITH DEVIATING ARGUMENTS 9 which is the same as in equation (1.1) and satisfies all the assumptions. By applying Theorem 2.7 we obtain a unique strong solution of (4.1). Acknowledgements. D. Chutia wants to thank the DST INSPIRE for their grant DST/INSPIRE Fellowship/2017/IF170509. R. Haloi wants to acknowledge funding from NBHM (Grant No. 02011/9/2019 NBHM(R.P.)/R, D II/1324), and the DST MATRICS (Grant No. SERB/F/12082/2018-2019). References [1] S. Agarwal, D. Bahuguna; Method of semidiscretization in time to nonlinear retarded differ- ential equation with nonlocal history conditions, IJMMS, 2004 (2004), 1943–1956. [2] D. Bahuguna, V. Raghavendra; Application of Rothe’s method to nonlinear Schrodinger type equations, Appl. Anal., 31(1988), no. 1–2, 149–160. [3] K. Bartosz; Convergence of Rothe scheme for a class of dynamic variational inequalities involving Clarke subdifferential, Appl. Anal., 97(2018), no. 13, 2189–2209. [4] K. Bartosz, M. Sofonea; The Rothe method for variational-hemivariational inequalities with applications to contact mechanics, SIAM J. Math. Anal.,48(2016), 861–883. [5] A. Bouziani; Application of Rothe’s method to a semilinear hyperbolic equation, Georgian Math. J., 17 (2010), no. 3, 437–458. [6] A. Chaoui, A. Hallaci; On the solution of a fractional diffusion integrodifferential equation with Rothe time discretization, Numer. Func. Anal. Opt., 39 (2018), no. 6 , 643–654. [7] S. A. Dubey; The method of lines applied to nonlinear nonlocal functional differential equa- tions, J. Math. Anal. Appl., 376 (2011), no. 1, 275–281. [8] L. E. El’sgol’ts, S. B. Norkin; Introduction to the theory of differential equations with devi- ating arguments, Academic Press, 1973. [9] C. G. Gal; Nonlinear abstract differential equations with deviated argument, J. Math. Anal. Appl., 333 (2007), no. 2, 971–983. [10] R. Haloi; Solutions to quasi-linear differential equations with iterated deviating arguments, Electron. J. Differ. Eq., 2014 (2014), no. 249, 1–13. [11] R. Haloi, D. Bahuguna, D. N. Pandey; Existence and uniqueness of solutions for quasi-linear differential equations with deviating arguments, Electron. J. Differ. Eq., 2012 (2012), no. 13, 1–10. [12] R. Haloi, D. N. Pandey, D. Bahuguna; Existence and Uniqueness of a Solution for a Non- Autonomous Semilinear Integro-Differential Equation with Deviated Argument, Differ. Equ. Dyn. Syst.,20 (2012), no. 1, 1–16. [13] R. Haloi, D. N. Pandey, D. Bahuguna; Existence, uniqueness and asymptotic stability of so- lutions to non-autonomous semi-linear differential equations with deviated arguments, Non- linear Dynamics and System Theory, 12 (2012), no. 2, 179–191. [14] R. Haloi, D. N. Pandey, D. Bahuguna; On Solutions to a Nonautonomous Neutral Differential Equation with Deviating Arguments, Nonlinear Dynamics and System Theory, 13 (2012), no. 3, 242-257. [15] T. Kato; Nonlinear semigroups and evolution equations, J. Math. Soc. Jpn., 19 (1967), no. 4, 508–520. [16] J. Kačur; Application of Rothe’s method to nonlinear evolution equations, Mat. časopis, 25 (1975), no. 1, 63–81. [17] P. Kumar, D. N.Pandey, D. Bahuguna; Approximations of solutions to a fractional differen- tial equation with a deviating argument, Differ. Equ. Dyn. Syst., 22(2014), no. 4, 333–352. [18] N. Merazga, A. Bouziani; Rothe method for a mixed problem with an integral condition for the two dimensional diffusion equation, Abstr. Appl. Anal., 16 (2003), 899–922. [19] S. Migórski, S. Zeng; Rothe method and numerical analysis for history-dependent hemivari- ational inequalities with applications to contact mechanics, Numer. Algorithms, 82 (2019), no. 2, 423–450. [20] S. Migórski, S. Zeng ; The Rothe method for multi-term time fractional integral diffusion equations, Discrete Cont. Dyn.-B, 24(2019), no. 2, 719–735. [21] A. Pazy; Semigroups of Linear Operators and Applications to Partial Differential Equations, Applied Mathematical Sciences 44, Springer-Verlag, New York, 1983. 10 D. DEVI, D. CHUTIA, R. HALOI EJDE-2020/120 [22] A. Raheem, D. Bahuguna; A study of delayed cooperation diffusion system with Dirichlet boundary conditions, Appl. Math. Comput., 218 (2011), 4169–4176. [23] A. Raheem; D. Bahuguna; Rothe’s method for solving some fractional integral diffusion equation, Appl. Math. Comput., 236 (2014), 161–168. [24] K. Rektorys; On application of direct variational methods to the solution of parabolic bound- ary value problems of arbitrary order in the space variables, Czech. Math. J., 21 (1971), no. 2, 318–339. [25] E. Rothe; Zweidimensionale parabolische Randwertaufgaben als Grenzfall eindimensionaler Randwertaufgaben, Math. Ann., 102 (1930), 650–670 (in German). Darshana Devi Department of Mathematical Sciences, Tezpur University, Sonitpur, Assam, Pin 784028, India Email address: darsana.mou@gmail.com Duranta Chutia Department of Mathematical Sciences, Tezpur University, Sonitpur, Assam, Pin 784028, India Email address: durantachutia123@gmail.com Rajib Haloi Department of Mathematical Sciences, Tezpur University, Sonitpur, Assam, Pin 784028, India Email address: rajib.haloi@gmail.com, Phone +913712-275511, Fax +913712-267006 1. Introduction 2. Preliminaries and main result 3. Approximation 4. Application Acknowledgements References