=Paper= {{Paper |id=Vol-1894/num2 |storemode=property |title=Compact difference scheme for semi-linear delayed diffusion wave equation with fractional order in time |pdfUrl=https://ceur-ws.org/Vol-1894/num2.pdf |volume=Vol-1894 |authors=Ahmed S. Hendy,Vladimir G. Pimenov }} ==Compact difference scheme for semi-linear delayed diffusion wave equation with fractional order in time== https://ceur-ws.org/Vol-1894/num2.pdf
Compact difference scheme for semi-linear delayed diffusion
      wave equation with fractional order in time

                           Ahmed S. Hendy1,2                           Vladimir G. Pimenov1,3
                        ahmed.hendy@fsc.bu.edu.eg                       v.g.pimenov@urfu.ru
      1 – Institute of Natural Sciences and Mathematics, Ural Federal University (Yekaterinburg, Russia)
                       2 – Department of Mathematics, Benha University (Benha, Egypt)
                 3 – Krasovskii Institute of Mathematics and Mechanics (Yekaterinburg, Russia)




                                                        Abstract
                       A compact difference scheme for a class of non-linear fractional
                       diffusion-wave equations with fixed time delay is considered. Analysis
                       of the constructed difference scheme is done in L∞ -norm by means of
                       the discrete energy method. A numerical test example is introduced to
                       illustrate the accuracy and efficiency of the proposed method.




1    Introduction
An important class of fractional differential equations which has been studied widely in recent years is the
time fractional diffusion-wave equation (FDWE). The time FDWE is obtained from the classical diffusion-wave
equation by replacing the second-order time derivative term by a fractional derivative of order 1 < α ≤ 2.
The fractional diffusion equation was introduced in physics by Nigmatullin [16] to describe diffusion in media
with fractal geometry, which is a special type of porous media. Gorenflo et al. [10] presented the scale-invariant
solutions for the time-fractional diffusion-wave equation in terms of the generalized Wright function. Agrawal [2]
extended this formulation to a diffusion-wave equation that contains a fourth-order space derivative term in a
bounded space domain. Recently, simulations of the approximation solutions of time-fractional wave, forced wave
(shear wave) and damped wave equations are given in [1]. A novel fractional diffusion-wave equation with non-
local regularization for noise removal was presented in [24]. The existence and uniqueness of solutions for Dirichlet
initial-boundary value problem associated to the semi linear fractional wave equation was recently studied in [14].
As a numerical approach to solve FDWE, Sun and his co-authors proposed a high order difference methods for the
fractional diffusion-wave equation [8]. Also, in [22], the efforts of the authors were devoted to the application of
fractional multi-step method to obtain a numerical solution of time fractional diffusion-wave equation. Compact
finite difference schemes for the modified anomalous fractional sub-diffusion equation and fractional diffusion-
wave equation were studied in [21]. A numerical solution for a general class of diffusion problem was considered
in [3], where the standard time derivative is replaced by a fractional one. An efficient numerical method was
constructed in [26] to solve this moving boundary problem.
   Time delay occurs in many realistic applications which are modeled mathematically, e.g. [9, 6, 13, 4, 15, 5].
Reaction-diffusion equations with time delay effect have been proposed as models for the population ecology, the
cell biology and the control theory in recent years [19]. The existence of mild solutions for initial value problem
for nonlinear time fractional non-autonomous evolution equations with delay in Banach space E was studied
in [7]. Numerically, a linearized quasi-compact difference scheme was proposed for semi-linear space-fractional

Copyright c by the paper’s authors. Copying permitted for private and academic purposes.
In: A.A. Makhnev, S.F. Pravdin (eds.): Proceedings of the International Youth School-conference «SoProMat-2017», Yekaterinburg,
Russia, 06-Feb-2017, published at http://ceur-ws.org




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diffusion equations with a fixed time delay [11]. A linearized compact finite difference scheme was presented for
the semi-linear fractional delay convection-reaction–diffusion equation in [23]. The authors of the manuscript at
hand, recently proposed a difference scheme for a class of non-linear delay distributed order fractional diffusion
equations in [17]. As an extension to this contribution and depending on Sun ’s work [20], we seek to derive a
compact linear difference scheme to solve numerically FDWE effected with a non-linear delayed source function,
more specific we consider

                       ∂ α u(x, t)    ∂ 2 u(x, t)
                             α
                                   =K             + f (x, t, u(x, t), u(x, t − s)), t > 0, 0 ≤ x ≤ L,                  (1a)
                           ∂t             ∂x2
with the following initial and boundary conditions

                                                                               ∂u(x, 0)               ∂ r̃(x, t)
                   u(x, t) = r̃(x, t),    0 ≤ x ≤ L,          t ∈ [−s, 0],              = ψ̃(x) = lim            ,     (1b)
                                                                                 ∂t              t→−0     ∂t
                   u(0, t) = φ0 (t),     u(L, t) = φL (t),         t > 0,                                              (1c)

where s > 0 is the delay parameter, K is a positive constant. The fractional derivative of order 1 < α ≤ 2 is
defined in Caputo sense.
   In order to transform (1) to a system with zero Dirichlet boundary conditions, we define h(x, t) := φ0 (t) +
x
L (φL (t) − φ0 (t)) and introduce the new function v(x, t) = u(x, t) − h(x, t). Hence, we have

                        ∂ α v(x, t)     ∂ 2 v(x, t)
                                    = K             + f (x, t, v(x, t), v(x, t − s)), t > 0, 0 ≤ x ≤ L,                (2a)
                            ∂tα             ∂x2
with the following initial and boundary conditions

                                                                               ∂v(x, 0)              ∂r(x, t)
                   v(x, t) = r(x, t),     0 ≤ x ≤ L,          t ∈ [−s, 0],              = ψ(x) = lim          ,        (2b)
                                                                                 ∂t             t→−0   ∂t
                   v(0, t) = v(L, t) = 0,      t > 0.                                                                  (2c)

   We need to overcome two degrees of complexity; how to employ a suitable approximation of the time fractional
derivative on the one hand, and how to approximate the non linear delay source function linearly on the other,
in order to obtain a numerical solution for (2). Throughout this work and by the aid of [23], we suppose that the
function f (x, t, µ, v) and the solution u(x, t) of (2) are sufficiently smooth in the following sense:
    • Let m be an integer
                        Smsatisfying ms ≤ T < (m + 1)s, define Ir = (rs, (r + 1)s), for r = −1, 0, . . . , m − 1,
      Im = (ms, T ), I = q=−1 Iq and assume that u(x, t) ∈ C (6,3) ([0, L] × [0, T ]),
    • The partial derivatives fµ (x, t, µ, v) and fv (x, t, µ, v) are continuous in the 0 -neighborhood of the solution.
      Define

                                  c1 =         sup            |fµ (x, t, u(x, t) + 1 , u(x, t − s) + 2 )| ,          (3a)
                                         0                         |aij |;
                                                                                                             j6=i

                                              10 bα0  K                         1 bα0   K
                                      aii =          + 2,         ai+1,i =            − 2 = ai−1,i .
                                              12 µ̄τ  h                        12 µ̄τ  2h
Therefore, the coefficient matrix is nonsingular and the theorem is readily proved by strong induction.                          

3       Convergence and stability for the difference scheme
Now, we introduce the uniqueness, stability and convergence theorems in L∞ -norm using the discrete energy
method for the proposed difference scheme.
The spatial domain [0, L] is covered by Ωh = {xi | 0 ≤ i ≤ M, } and let Vh = {v | v = (v0 , . . . , vM ), v0 = vM =
0} be a grid function space on Ωh . For any u, v ∈ Vh , define the discrete inner products and corresponding norms
as
                                     M
                                     X −1                          M
                                                                   X
                          hu, vi = h      ui vi , hδx u, δx vi = h   (δx ui−1/2 )(δx vi−1/2 ),
                                              i=1                                i=1

                                                                          1
                                       hδx2 u, vi = −hδx u, δx vi, δx ui = (ui − ui−1 ),
                                                                          h
                                        p                    p
                                  kuk = hu, ui, |u|1 = hδx u, δx ui, kuk∞ = max |u|,
                                                                                                     0≤i≤M

and denote                                    v                                  v
                                              u M                                u M −1
                                              u X                                u X
                                                                         2
                                       |v|1 = th  (δx vi )2 ,          kδx vk∞ = th    (δx2 vi )2 .
                                                     i=1                                    i=1

According to [25], the following inequalities are fulfilled
                                                  √
                                                    L                              L
                                       kuk∞ ≤         |u|1 ,                 kuk ≤ √ |u|1 .                                    (11)
                                                   2                                6
For the analysis of the difference scheme, we will use the following lemmas:
  Lemma 3. Let v ∈ Vh , we have kδx2 vk ≤ h2 |v|1 .
                                                                                                 √
    Lemma 4. [18] Let v ∈ Vh and v0 = vM = 0. Then, we have kvk∞ ≤ 2L |v|1 .
    Lemma 5. [20] For any G = {G1 , G2 , G3 , . . .} and ψ, we obtain
            m
                "         k−1
                                                            #                    m
                                                                      1−αl                  2−αl
           X
                   α
                          X α            αl            αl            tm          X         tm
                  b0 Gk −     (bk−j−1 − bk−j )Gj − bk−1 ψ Gk ≥
                                 l
                                                                               τ   G2k −             ψ2 .
                          j=1
                                                                   2(2 − α l )           2(2 − α l )
                   k=1                                                                               k=1




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   Lemma 6. Gronwall inequality [25]. Suppose that {F k | k ≥ 0} is a nonnegative sequence and satisfies
    k+1
               Pk
F     ≤ A + Bτ l=1 F l , k ≥ 0, for some nonnegative constants A and B. Then F k+1 ≤ A exp(Bkτ ).
   Theorem 2. (Convergence). Let v(x, t) ∈ [0, L]×[−s, T ], be the solution of (2) such that v(xi , tk ) = Vik and
vi (0 ≤ i ≤ M, −n ≤ k ≤ N ) be the solution of the difference scheme (9), denote eki = Vik − vik , for 0 ≤ i ≤ M ,
 k

−n ≤ k ≤ N ,                  r
                                   3L       3T                     1
                          C=           exp       (5c21 + c22 ) , θ = T α−1 Γ(3 − α),
                                  8θK        8θK                     2
then if
                                                   1
                                               3−α                  41
                                               0                       0
                                   τ ≤ τ0 =            , h ≤ h0 =            ,                                (12)
                                              4C                      4C
one has that
                                    k ek k∞ ≤ C τ 3−α + h4 , 0 ≤ k ≤ N,
                                                              
                                                                                                              (13)
where c1 , c2 and 0 are those from (3).
  The proof uses the previous formulated lemmas in the sense of our results in [12].

   To discuss the stability of the difference scheme (9), we also use the discrete energy method in the same way
like the discussion of the convergence. Let {zik | 0 ≤ i ≤ M, 0 ≤ k ≤ N } be the solution of
                                                                    
                          k−1
       1          k−1/2
                          X                       j−1/2
   A  bα  0 δt zi     −     (bα        α
                                k−j−1 − bk−j )δt zi     − bα
                                                           k−1 ψ(xi )
                                                                      
       µ̄                 j=1
                                                                                                       
                                                  k−1/2                   1     1       1         1
                                        = Kδx2 zi       + Af xi , tk−1/2 , zik + zik−1 , zik−n−1 + zik−n , (14a)
                                                                          2     2       2         2
such that 1 ≤ i ≤ M − 1,     1 ≤ k ≤ N, and supplied by appropriate initial and boundary conditions
                                  z0k = φ0 (tk ),     k
                                                     zM = φL (tk ),         1 ≤ k ≤ N,                            (14b)
                                  zik = r(xi , tk ) + ρki ,       0 ≤ i ≤ M,     −n ≤ k ≤ 0,                      (14c)

where ρki is the perturbation of ψ(xi , tk ).
Following the same steps as in the proof of the convergence theorem, the stability of the scheme is obtained.
Theorem 3. (Stability). Let θik = zik − vik , for 0 ≤ i ≤ M, −n ≤ k ≤ N. Then there exist some arbitrary
positive constants c4 , c5 , h0 , τ0 which fulfill
                                                                           v
                                                0                          u M −1
                              k
                                         √    X
                                                     k                k
                                                                           u X
                            kθ k∞ ≤ c4 τ           kρ k, 0 ≤ k ≤ N, kρ k = th     (ρki )2 ,
                                           k=−n                                                 i=1

conditioned by
                                         h ≤ h0 ,     τ ≤ τ0 ,          max |ρki | ≤ c5 .
                                                                      −n≤k≤0
                                                                      0≤i≤M



4     Numerical Verification
Let νik be the solution of the constructed difference scheme (9) with the step sizes τ and h. Define the maximum
norm error by E(τ, h) = max kVik − νik k∞ . Also, define the following error rates
                         0≤i≤M
                         0≤k≤N
                                                                                                 
                                                  E(2τ, h)                               E(τ, 2h)
                              rate1 = log2                        ,   rate2 = log2                      .
                                                  E(τ, h)                                E(τ, h)
Consider the following numerical test example
                   ∂ α u(x, t)   ∂ 2 u(x, t)
                               =             + f (x, t, u(x, t), u(x, t − s)),           t ∈ (0, 1), 0 < x < π,   (15a)
                       ∂tα           ∂x2




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                                                         Γ(4)
f (x, t, u(x, t), u(x, t − s)) = sin(x) (t3 + 2t + 4) + Γ(4−α) t3−α − u(x, t − s) + sin(x)((t − s)3 + 2(t − s) + 4),
with the following initial and boundary conditions

                         u(x, t) = (t3 + 2t + 4) sin(x),   0 ≤ x ≤ π,    t ∈ [−s, 0),   s > 0,                   (15b)

                                          u(0, t) = u(π, t) = 0,   t ∈ [0, 1].                                   (15c)
The exact solution of this problem is
                                            u(x, t) = (t3 + 2t + 4) sin(x).                                        (16)
Results are presented in Tables (1) - (2) (time) and Table 3 (space). From these numerical results, we can see a
good agreement between theoretical and numerical results.

Table 1: Errors and convergence order of the difference scheme (9) for (15) in time variable with α = 1.25,
h = π/3000 and with time delay s = 1.

                                              τ       E(τ, h)       rate1
                                              1
                                             10       0.00015
                                              1
                                             20       0.00004       1.732
                                              1
                                             40       0.00001       1.738
                                              1
                                             80    4.049 × 10−6     1.741
                                              1
                                             160   1.209 × 10−6     1.744
                                              1
                                             320   3.597 × 10−7     1.749



Table 2: Errors and convergence order of the difference scheme (9) for (15) in time variable with α = 1.75,
h = π/3000 and with time delay s = 41 .

                                              τ       E(τ, h)       rate1
                                              1
                                             40       0.00003
                                              1
                                             80       0.00001       1.232
                                              1
                                             160   5.415 × 10−6     1.238
                                              1
                                             320   2.288 × 10−6     1.243
                                              1
                                             640   9.625 × 10−7     1.249



Table 3: Errors and convergence order of the difference scheme (9) for (15) in space variable with α = 1.5,
τ = 1/10000 and with time delay s = 12 .
                                          h       E(τ, h)     rate2
                                          π
                                          4      0.00027
                                          π
                                          8      0.000018     3.872
                                          π                −6
                                         16   1.2525 ×  10    3.880
                                          π
                                         32  8.24587 × 10−8 3.925
                                          π
                                         64  5.28023 × 10−9 3.965
                                          π
                                         128 3.33926 × 10−10 3.983


Acknowledgements
This work was supported by Government of the Russian Federation Resolution N 211 of March 16, 2013.

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