9
Journal of the European Optical Society-Rapid Publications González-Gaxiola et al. Journal of the European Optical Society-Rapid Publications (2019) 15:13 https://doi.org/10.1186/s41476-019-0111-6 RESEARCH Open Access Optical soliton perturbation of Fokas-Lenells equation by the Laplace-Adomian decomposition algorithm O. González-Gaxiola 1* , Anjan Biswas 2,3,4 and Milivoj R. Belic 5 Abstract This paper displays numerical simulation for bright and dark optical solitons that emerge from Fokas-Lenells equation which is studied in the context of dispersive solitons in polarization-preserving fibers. The Laplace-Adomian decomposition scheme is the numerical tool adopted in the paper. The numerical results, for bright and dark solitons, are expository and therefore supplement the analytical developments, thus far. Keywords: Fokas-lenells equation, Polarization-preserving fibers, Adomian decomposition method, Optical solitons solutions, Perturbation Introduction One of the governing models to study dispersive soli- tons is Fokas-Lennels equation (FLE) [113]. In such a model, in addition to group velocity dispersion (GVD), one considers, inter-modal dispersion as well as nonlin- ear dispersion thus treating it with a flavor of additional dispersive effects. There has been a plethora of analyti- cal tools that have been implemented to study FLE. They range from semi-inverse variational principle, Lie sym- metry analysis, Riccati equation approach, exp-function method, traveling wave hypothesis, trial function method and further wide varieties. This paper will be changing gears to study the model from a different perspective. One of the very many and modern numerical algorithms that will be implemented is the Laplace-Adomian decomposi- tion integration scheme. This method has been success- fully applied to variety of other models from optics [1416]. This paper now studies FLE, for the first time, by the aid of Laplace-Adomian decomposition scheme. The details are sketched in the remainder of the paper, after introducing the model. *Correspondence: [email protected] 1 Departamento de Matemáticas Aplicadas y Sistemas, Universidad Autónoma Metropolitana-Cuajimalpa, Vasco de Quiroga 4871, 05348, Mexico City, Mexico Full list of author information is available at the end of the article The Fokas-Lenells equation (FLE) in presence of perturbation terms The dimensionless form of the perturbed Fokas-Lenells equation (FLE) is given by iu t + a 1 u xx + a 2 u xt +|u| 2 (bu + iσ u x ) = i αu x + λ ( |u| 2 u ) x + μ ( |u| 2 ) x u . (1) This equation was first studied in [1724] and arises in various systems such as water waves, plasma physics, solid state physics and nonlinear optics. In Eq. (1), u(x, t ) repre- sents a complex field envelope, and x and t are spatial and temporal variables, respectively. Here, the coefficient a 1 is the group velocity dispersion (GVD) and a 2 is the spatio- temporal dispersion (STD) the coefficient b is self-phase modulation moreover σ accounts for nonlinear disper- sion. In the perturbative term of Eq. (1), the first term represents the inter-modal dispersion (IMD), the sec- ond term is the self-steepening effect and finally the last term accounts for another version of nonlinear dispersion (ND). Bright optical solitons The bright optical soliton solution to (1) is given by [5, 11]: u(x, t ) = A sech [(x ν t )] e i[κ x+ωt+θ ] . (2) Here, ν is the soliton velocity, κ is the soliton frequency, ω is the angular velocity and θ is the phase center. © The Author(s). 2019 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

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Page 1: RESEARCH OpenAccess Opticalsolitonperturbationof Fokas ...Keywords: Fokas-lenellsequation,Polarization-preservingfibers,Adomiandecompositionmethod,Opticalsolitons solutions,Perturbation

Journal of the European OpticalSociety-Rapid Publications

González-Gaxiola et al. Journal of the European Optical Society-RapidPublications (2019) 15:13 https://doi.org/10.1186/s41476-019-0111-6

RESEARCH Open Access

Optical soliton perturbation ofFokas-Lenells equation by theLaplace-Adomian decomposition algorithmO. González-Gaxiola1*, Anjan Biswas2,3,4 and Milivoj R. Belic5

Abstract

This paper displays numerical simulation for bright and dark optical solitons that emerge from Fokas-Lenells equationwhich is studied in the context of dispersive solitons in polarization-preserving fibers. The Laplace-Adomiandecomposition scheme is the numerical tool adopted in the paper. The numerical results, for bright and dark solitons,are expository and therefore supplement the analytical developments, thus far.

Keywords: Fokas-lenells equation, Polarization-preserving fibers, Adomian decomposition method, Optical solitonssolutions, Perturbation

IntroductionOne of the governing models to study dispersive soli-tons is Fokas-Lennels equation (FLE) [1–13]. In such amodel, in addition to group velocity dispersion (GVD),one considers, inter-modal dispersion as well as nonlin-ear dispersion thus treating it with a flavor of additionaldispersive effects. There has been a plethora of analyti-cal tools that have been implemented to study FLE. Theyrange from semi-inverse variational principle, Lie sym-metry analysis, Riccati equation approach, exp-functionmethod, traveling wave hypothesis, trial function methodand further wide varieties. This paper will be changinggears to study the model from a different perspective. Oneof the very many and modern numerical algorithms thatwill be implemented is the Laplace-Adomian decomposi-tion integration scheme. This method has been success-fully applied to variety of other models from optics [14–16]. This paper now studies FLE, for the first time, bythe aid of Laplace-Adomian decomposition scheme. Thedetails are sketched in the remainder of the paper, afterintroducing the model.

*Correspondence: [email protected] de Matemáticas Aplicadas y Sistemas, Universidad AutónomaMetropolitana-Cuajimalpa, Vasco de Quiroga 4871, 05348, Mexico City, MexicoFull list of author information is available at the end of the article

The Fokas-Lenells equation (FLE) in presence ofperturbation termsThe dimensionless form of the perturbed Fokas-Lenellsequation (FLE) is given by

iut + a1uxx + a2uxt + |u|2 (bu + iσux)= i

[αux + λ

(|u|2u)x + μ

(|u|2)x u].

(1)

This equation was first studied in [17–24] and arises invarious systems such as water waves, plasma physics, solidstate physics and nonlinear optics. In Eq. (1), u(x, t) repre-sents a complex field envelope, and x and t are spatial andtemporal variables, respectively. Here, the coefficient a1 isthe group velocity dispersion (GVD) and a2 is the spatio-temporal dispersion (STD) the coefficient b is self-phasemodulation moreover σ accounts for nonlinear disper-sion. In the perturbative term of Eq. (1), the first termrepresents the inter-modal dispersion (IMD), the sec-ond term is the self-steepening effect and finally the lastterm accounts for another version of nonlinear dispersion(ND).

Bright optical solitonsThe bright optical soliton solution to (1) is given by [5, 11]:

u(x, t) = A sech [(x − νt)] ei[−κx+ωt+θ ]. (2)

Here, ν is the soliton velocity, κ is the soliton frequency, ωis the angular velocity and θ is the phase center.

© The Author(s). 2019 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, andreproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to theCreative Commons license, and indicate if changes were made.

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González-Gaxiola et al. Journal of the European Optical Society-Rapid Publications (2019) 15:13 Page 2 of 9

The amplitude A of the soliton in this case is given by

A = ±√

2(a1 − a2ν)

b − κλ + κσ, (3)

where, the velocity of the soliton in relation to the coeffi-cients that appear in the Eq. (1) is

ν = α + 2a1κ − a2ωa2κ − 1

, (4)

and the constraints conditions on the parameters are

a2κ �= 1, 3λ + 2μ − σ = 0. (5)

In the previous context κ is any parameter that satisfiesthe Eq. (5).

Dark optical solitonsnoindent The dark optical soliton solution to (1) is givenby [5, 11]:

u(x, t) = B tanh [(x − νt)] ei[−κx+ωt+θ ]. (6)

Here, ν is the soliton velocity, κ is the soliton frequency, ωis the angular velocity and θ is the phase center.The amplitude B of the soliton in this case is given by

B = ±√−2(a1 − a2ν)

b − κλ + κσ, (7)

where, the velocity of the soliton in relation to the coeffi-cients that appear in the Eq. (1) is

ν = α + 2a1κ − a2ωa2κ − 1

, (8)

and the constraints conditions on the parameters are

a2κ �= 1, 3λ + 2μ − σ = 0. (9)

In the previous context κ is any parameter that satisfiesthe Eq. (9).

The Laplace Adomian DecompositionMethod(LADM)To illustrate the basic concept of Laplace-Adomiandecomposition algorithm, we consider the general formof second order nonlinear partial differential equations inthe form

F (u(x, t)) = 0, (10)with initial conditions

u(x, 0) = f (x), ux(x, 0) = g(x). (11)

where F is a differential operator. Now, let us decomposethis operator as F = L+R+N where L(u) = ∂u

∂t stands fora linear differential operator. The operators R and N arethe remaining linear and nonlinear parts, respectively.With these considerations, Eq. (10) can now be rewrittenas

Lu(x, t) = Ru(x, t) + Nu(x, t). (12)

Solving for Lu(x, t) and applying the Laplace transformrespect to t to Eq. (12), gives

L {Lu(x, t)} = L {Ru(x, t) + Nu(x, t)} . (13)

Thus, Eq. (13) turns out to be equivalent to

su(x, s) − u(x, 0) = L {Ru(x, t) + Nu(x, t)} . (14)

Using Eq. (11), one get

u(x, s) = f (x)s

+ 1sL {Ru(x, t) + Nu(x, t)} . (15)

Finally, by applying inverse Laplace transformation L−1

on both sides of the Eq. (15), we obtain

u(x, t) = f (x) + L−1[1sL{Ru(x, t) + Nu(x, t)}

]. (16)

The Laplace-Adomian decomposition algorithmassumes the solution u(x, t) can be expanded into infiniteseries given by

u(x, t) =∞∑n=0

un(x, t). (17)

Moreover, Also the nonlinear operator N is decomposedas

Nu(x, t) =∞∑n=0

An(u0,u1, . . . ,un), . (18)

Each An is an Adomian polynomial of u0,u1, . . . ,un thatcan be calculated for all forms of nonlinearity accordingto the following formula [25–27]:

A0 = N(u0),

An = 1n

m∑i=1

n−1∑k=0

(k + 1)ui,k+1∂

∂ui,0An−1−k , n ≥ 1.

(19)

Therefore Adomian’s polynomials are given byA0 = N(u0)A1 = u1N ′(u0)A2 = u2N ′(u0) + 1

2u21N ′′(u0)

A3 = u3N ′(u0) + u1u2N ′′(u0) + 13!u

31N (3)(u0)

A4 = u4N ′(u0)+( 12u

22 + u1u3

)N ′′(u0)+ 1

2!u21u2N (3)(u0)+

14!u

41N (4)(u0)

...All other polynomials are calculated in a similar way.Substituting (17) and (18) into Eq. (16) gives rise to

∞∑n=0

un(x, t) =f (x) + L−1[1sL

{R

∞∑n=0

un(x, t)

+∞∑n=0

An(u0,u1, . . . ,un)}]

.(20)

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Table 1 Bright optical solitons

Cases a1 a2 b σ α λ μ ν κ A N |Max Error|1 1.00 0.50 2.00 1.00 2.00 1.00 −1.00 −1.66 0.50 0.27 12 2.10 × 10−10

2 3.00 0.16 1.00 1.00 2.00 1.00 −1.00 −3.47 0.25 2.67 12 3.00 × 10−10

3 1.50 0.25 3.00 1.00 1.00 −1.00 2.00 −5.00 1.00 0.31 12 1.50 × 10−10

4 0.20 0.33 4.00 2.00 2.00 2.00 −2.00 −7.40 2.00 1.45 12 1.00 × 10−10

Hence, Eq. (20) suggests the following iterative algorithm{u0(x, t) = f (x),un+1(x, t) = L−1 [ 1

s L {Run(x, t) + An(u0,u1, . . . ,un)}], n = 0, 1, 2, . . .

(21)

Finally, after determining un’s, the N-term truncatedapproximation of the solution is obtained as

uN (x, t) =N−1∑n=0

un(x, t), N ≥ 1. (22)

From this analysis it is evident that, the Adomian decom-position method, combined with the Laplace transformrequires less effort in comparison with the traditionalAdomian decomposition method. This method consider-ably decreases the number of calculations. In addition,Adomian decomposition procedure is easily establishedwithout requiring to linearize the problem.

Solution of the perturbed Fokas-Lenells equationby LADMIn this section, we outline the application of LADM toobtain explicit solution of Eq. (1) with the initial condi-tions u(x, 0) = f (x), ux(x, 0) = g(x).

Let us consider the dimensionless form of the perturbedFokas-Lenells equation Eq. (1) in an operator form

Lu(x, t)+Ru(x, t)+N1u(x, t)+N2u(x, t)+N3u(x, t) = 0(23)

where the notation N1u = −i|u|2(bu + iσux),N2u = −λ(|u|2u)x and N3u = −μu(|u|2)x symbol-ize the nonlinear term, respectively. The notation Ru =− (αux + ia1uxx + ia2uxt) symbolize the linear differen-tial operator and Lu = ut simply means derivative withrespect to time.The LADM represents solution as an infinite series ofcomponents given below,

u(x, t) =∞∑n=0

un(x, t). (24)

The nonlinear terms N1u, N2u and N3u can be decom-posed into infinite series of Adomian polynomials givenby:

N1u = −i|u|2(bu + iσux) =∞∑n=0

Pn(u0,u1, . . . ,un),

(25)

Fig. 1 Dynamic evolution profile of |u|2 via LADM (left) and contour plot of the wave amplitude of |u|2 (right) for the values of the parameters usedin case 1 with |Max Error| = 2.1 × 10−10

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Fig. 2 Dynamic evolution profile of |u|2 via LADM (left) and contour plot of the wave amplitude of |u|2 (right) for the values of the parameters usedin case 2 with |Max Error| = 3.0 × 10−10

N2u = −λ(|u|2u)

x =∞∑n=0

Qn(u0,u1, . . . ,un), (26)

andN3u = −μu

(|u|2)x =∞∑n=0

Rn(u0,u1, . . . ,un). (27)

Here Pn, Qn and Rn are the Adomian polynomials andcan be calculatedby the formula givenby the Eq. (19), that is,

P0 = N1(u0), Q0 = N2(u0), R0 = N3(u0),

and for every n ≥ 1 we have

Pn = 1n

m∑i=1

n−1∑k=0

(k + 1)ui,k+1∂

∂ui,0Pn−1−k , (28)

Fig. 3 Dynamic evolution profile of |u|2 via LADM (left) and contour plot of the wave amplitude of |u|2 (right) for the values of the parameters usedin case 3 with |Max Error| = 1.5 × 10−10

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Fig. 4 Dynamic evolution profile of |u|2 via LADM (left) and contour plot of the wave amplitude of |u|2 (right) for the values of the parameters usedin case 4 with |Max Error| = 1.0 × 10−10

Qn = 1n

m∑i=1

n−1∑k=0

(k + 1)ui,k+1∂

∂ui,0Qn−1−k , (29)

Rn = 1n

m∑i=1

n−1∑k=0

(k + 1)ui,k+1∂

∂ui,0Rn−1−k . (30)

The first few Adomian polynomials are given by

P0 = −ibu20u0,

P1 = −2ibu0u1u0 − ibu20u1,

P2 = −2ibu0u2u0 − ibu21u0 − 2ibu0u1u1 − ibu20u2,

P3 = −2ibu0u3u0 − 2ibu1u2u0 − 2ibu0u2u1 − ibu21u1− 2ibu0u1u2 − ibu20u3,

P4 = −ibu0u22 − 2ibu0u0u4 − 2ibu0u1u3 − 2ibu0u1u3− 2ibu1u1u2 + 2u0u2u2 − ibu21u2

− 2ibu0u1u3 − ibu20u4,...

Q0 = −(λ + μ)u20u0x,Q1 = −(λ + μ)

(u20u1x + 2u0u1u0x

),

Q2 =−(λ+μ)(u21u0x+u20u2x+2u0u1u1x+2u0u2u0x

),

Q3 = −(λ + μ)(u21u1x + u20u3x + 2u0u1u2x

+2u0u2u1x + 2u0u3u0x + 2u1u2u0x) ,Q4 = −(λ + μ)

(u22u0x+u21u2x+2u0u1u3x + 2u0u2u2x

+2u0u3u1x + 2u0u4u0x + 2u1u2u1x + 2u1u3u0x) ,...

R0 = (σ − 2λ − μ)u0u0u0x,R1 = (σ − 2λ − μ)(u0u0u1x + u0u1u0x + u1u0u0x),R2 = (σ − 2λ − μ) (u0u0u2x + u0u1u1x + u0u2u0x

+u1u0u1x + u1u1u0x + u2u0u0x) ,R3 = (σ − 2λ − μ) (u0u0u3x + u0u1u2x + u0u2u1x

+ u0u3u0x + u1u0u2x + u1u1u1x + u1u2u0x+u2u0u1x + u2u1u0x + u3u0u0x) ,

R4 = (σ − 2λ − μ) (u0u0u4x + u0u1u3x + u0u2u2x+ u0u3u1x + u0u4u0x + u1u0u3x + u1u1u2x+ u1u2u1x + u1u3u0x + u2u0u2x + u2u1u1x+u2u2u0x + u3u0u1x + u3u1u0x + u4u0u0x) ,

...

Table 2 Dark optical solitons

Cases a1 a2 b σ α λ μ ν κ B N |Max Error|5 2.00 0.25 1.00 −1.00 −2.00 1.00 −2.00 −2.33 1.00 1.68 12 2.50 × 10−10

6 1.50 0.20 −3.00 2.00 −1.00 0.33 0.50 −4.71 1.50 3.12 12 2.50 × 10−10

7 0.20 0.33 −4.00 2.00 2.00 2.00 −2.00 −7.40 2.00 1.15 12 1.00 × 10−10

8 3.00 0.16 −4.00 3.50 1.00 0.50 1.00 −10.04 1.20 4.83 12 1.50 × 10−10

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Fig. 5 Dynamic evolution profile of |u|2 via LADM (left) and contour plot of the wave amplitude of |u|2 (right) for the values of the parameters usedin case 5 with |Max Error| = 2.5 × 10−10

Then, the Adomian polynomials corresponding to thenonlinear part Nu = N1u + N2u + N3u are

A0 = −ibu20u0 − (λ + μ)u20u0x + (σ − 2λ − μ)u0u0u0x,A1 = −2ibu0u1u0−ibu20u1 −(λ + μ)(u20u1x + 2u0u1u0x)

+ (σ − 2λ − μ)(u0u0u1x + u0u1u0x + u1u0u0x),A2 = −2ibu0u2u0 − ibu21u0 − 2ibu0u1u1 − ibu20u2

− (λ + μ)(u21u0x + u20u2x + 2u0u1u1x + 2u0u2u0x

)+ (σ − 2λ − μ)(u0u0u2x + u0u1u1x + u0u2u0x

+ u1u0u1x + u1u1u0x + u2u0u0x),A3 = −2ibu0u3u0 − 2ibu1u2u0 − 2ibu0u2u1 − ibu21u1

− 2ibu0u1u2 − ibu20u3 − (λ + μ)(u21u1x + u20u3x+ 2u0u1u2x + 2u0u2u1x + 2u0u3u0x + 2u1u2u0x)

+ (σ − 2λ − μ) × (u0u0u3x + u0u1u2x + u0u2u1x+ u0u3u0x + u1u0u2x + u1u1u1x + u1u2u0x+ u2u0u1x + u2u1u0x + u3u0u0x),

Fig. 6 Dynamic evolution profile of |u|2 via LADM (left) and contour plot of the wave amplitude of |u|2 (right) for the values of the parameters usedin case 6 with |Max Error| = 2.5 × 10−10

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Fig. 7 Dynamic evolution profile of |u|2 via LADM (left) and contour plot of the wave amplitude of |u|2 (right) for the values of the parameters usedin case 7 with |Max Error| = 1.0 × 10−10

and so on for other Adomian polynomials.By applying the Laplace transform with respect to t on

both sides of the Eq. (23) and using the linearity of theLaplace transform gives:

L {Lu(x, t)} = −L{Ru(x, t)} − L {N1u(x, t)}− L {N2u(x, t)} − L {N3u(x, t)} . (31)

Because of the differentiation property of Laplace trans-form, Eq. (31) can be written as

sL{u(x, t)} − u(x, 0) = −L {Ru(x, t)} − L {N1u(x, t)}− L {N2u(x, t)} − L {N3u(x, t)} .

(32)

Thus,

L {u(x, t)} = 1su(x, 0) − 1

s(L {Ru(x, t)} + L {N1u(x, t)}

+L {N2u(x, t)} + L {N3u(x, t)}) .(33)

Fig. 8 Dynamic evolution profile of |u|2 via LADM (left) and contour plot of the wave amplitude of |u|2 (right) for the values of the parameters usedin case 8 with |Max Error| = 1.5 × 10−10

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By substituting (24), (25), (26) and (27) into (33), we obtain

L{ ∞∑n=0

un(x, t)}

= f (x)s

− 1s

(L

{R

∞∑n=0

un(x, t)}

+L{ ∞∑n=0

Pn

}+L

{ ∞∑n=0

Qn

}+L

{ ∞∑n=0

Rn

}).

(34)

Comparing both sides of the Eq. (34), the following rela-tions arise:

L {u0(x, t)} = f (x)s

(35)

L {u1(x, t)} = −1s

(L {Ru0(x, t)} + L {P0} + L {Q0} + L {R0})(36)

L {u2(x, t)}=−1s

(L {Ru1(x, t)}+L {P1}+L {Q1}+L {R1}) .(37)

In general, we get the following recursive algorithm

L {un+1(x, t)} = −1s

(L {Run(x, t)} + L {Pn}+L {Qn} + L {Rn}) , n ≥ 1.

(38)

Finally, by applying inverse Laplace transformation wededuce the following recurrence formulas for each n =0, 1, 2, . . . ,⎧⎨⎩u0(x, t) = f (x),un+1(x, t) = −L−1 [ 1

sL{Run(x, t) + Pn(u0, . . . ,un)+Qn(u0, . . . ,un) + Rn(u0, . . . ,un)}

].

(39)

Numerical simulations and graphical resultsWe perform numerical simulations for bright and darkoptical solitions.

Application to bright optical solitionsThe result and the profile of four cases are shown inTable 1 and in Figs. 1, 2, 3 and 4.

Application to dark optical solitionsThe result and the profile of four cases are shown inTable 2 and in Figs. 5, 6, 7 and 8.

ConclusionsThis paper successfully studied FLE in polarization-preserving fibers by the aid of Laplace-Adomian decom-position scheme. The numerical scheme yielded brightand dark soliton solutions. The results thus appear witha complete spectrum of soliton solutions. Although sin-gular solitons is a third form of solitons that emerge

from this model, it does not provide any interest withany kind of numerical scheme. The results of the paperare truly encouraging to study the methodology fur-ther along. Later, this scheme will be applied to vec-tor coupled FLE that studies solitons in birefringentfibers. Further along the model will be extended toaddress WDM/DWDM/UDWDM topology numerically.Such studies are currently under way.

AbbreviationsDWDM: Dense wavelength division multiplexing; FLE: Fokas-lennels equation;GVD: Group velocity dispersion; IMD: Inter-modal dispersion; LADM:Laplace-adomian decomposition method; ND: Nonlinear dispersion; STD:Spatio-temporal dispersion; UDWDM: Ultra-dense wavelength divisionmultiplexing; WDM: Wavelength-division multiplexing

AcknowledgmentsNot applicable.

Authors’ contributionsThe original ideas and results emerged from discussions among all theauthors. OGG wrote the manuscript with input from all authors. All authorsread and approved the final manuscript.

FundingThe research work of the third author (MRB) was supported by the grant NPRP8-028-1-001 from QNRF and he is thankful for it.

Availability of data andmaterialsNot applicable.

Competing interestsThe authors declare that they have no competing interests.

Author details1Departamento de Matemáticas Aplicadas y Sistemas, Universidad AutónomaMetropolitana-Cuajimalpa, Vasco de Quiroga 4871, 05348, Mexico City,Mexico. 2Department of Physics, Chemistry and Mathematics, Alabama A&MUniversity, Normal, AL, Huntsville 35762, USA. 3Department of Mathematics,King Abdulaziz University, 21589, Jeddah, Saudi Arabia. 4Department ofMathematics and Statistics, Tshwane University of Technology, 0008, Pretoria,South Africa. 5Science Program, Texas A&M University at Qatar, Doha, Qatar.

Received: 10 April 2019 Accepted: 28 May 2019

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