New integral transform: Shehu transform a generalization of Sumudu and Laplace transform for solving differential equations
NNEW INTEGRAL TRANSFORM: SHEHU TRANSFORM AGENERALIZATION OF SUMUDU AND LAPLACE TRANSFORMFOR SOLVING DIFFERENTIAL EQUATIONS
SHEHU MAITAMA ∗ , WEIDONG ZHAO Abstract.
In this paper, we introduce a Laplace-type integral transformcalled the Shehu transform which is a generalization of the Laplace and theSumudu integral transforms for solving differential equations in the time do-main. The proposed integral transform is successfully derived from the clas-sical Fourier integral transform and is applied to both ordinary and partialdifferential equations to show its simplicity, efficiency, and the high accuracy. Introduction
Historically, the origin of the integral transforms can be traced back to the workof P. S. Laplace in 1780s and Joseph Fourier in 1822. In recent years, differentialand integral equations have been solved using many integral transforms ([1]-[11]).The Laplace transform, and Fourier integral transforms are the most commonlyused in the literature. The Fourier integral transform [12] was named after theFrench mathematician Joseph Fourier. Mathematically, Fourier integral transformis defined as: (cid:122) [ f ( t )] = f ( ω ) = 1 √ π (cid:90) ∞−∞ exp ( − iωt ) f ( t ) dt. (1.1)The Fourier transform have many applications in physics and engineering processes[13]. The Laplace integral transform is similar with the Fourier transform and isdefined as: £ [ f ( t )] = F ( s ) = (cid:90) ∞−∞ exp ( − st ) f ( t ) dt. (1.2)The Laplace transform is highly efficient for solving some class of ordinary andpartial differential equations [14]. By replacing the variable iω with the variable s in Equ.(1.1), the well-known Fourier transform will become a Laplace transformand the vice-versa. The only difference between the Laplace transform, and theFourier transform is that the Laplace transform can be defined for both stableand unstable system while the Fourier transform can only be defined on a stablesystem. In mathematical literature, the discrete-time equivalent of the Laplacetransform called z-transform [15] converts a discrete-time signal into a complexfrequency-domain representation. The basic idea of the z-transform was known toLaplace and later it was re-introduced by the Jewish-Polish mathematician WitoldHurewicz to treat a sampled-data control systems used with radar in 1947 ([16]-[17]). In mathematics and signal processing, the bilateral or two-sided z-transform Mathematics Subject Classification.
Key words and phrases.
Shehu transform; Fourier integral transform; Laplace transform; nat-ural transform; Sumudu transform; ordinary and partial differential equations. a r X i v : . [ m a t h . G M ] A p r EW INTEGRAL TRANSFORM FOR SOLVING DIFFERENTIAL EQUATIONS 2 of a discrete-time signal x [ n ] is the normal power series X ( z ) which is defined as: X ( z ) = Z { x [ n ] } = ∞ (cid:88) n = −∞ x [ n ] z − n , (1.3)where n is an integer and z is in general a complex number [18].The multiplicative version of the two-sided Laplace transform called the Mellinintegral transform is defined as [19]: M [ f ( s ); s ] = f ∗ ( s ) = (cid:90) ∞ x s − f ( x ) dx. (1.4)The Mellin integral transform is similar with the Laplace transform and Fouriertransform and is widely applied in computer science and number theory due to itsinvariant property [20, 21]. In railway engineering, the Laplace-Carson transform[22] which is a Laplace-type integral transform named after Pierre Simon Laplaceand John Renshaw Carson is defined as:ˆ f C ( p ) = p (cid:90) ∞ exp ( − pt ) f ( t ) dt, t ≥ . (1.5)The Laplace-Carson integral transform have many applications in physics and en-gineering and can easily be converted into a Mellin deconvolution problem, see([23],[24]). In mathematics, the Hankel’s integral transform [25] which is similar tothe Fourier transform was first introduced by the German mathematician HermannHankel and was widely used in physical science and engineering [26]. The Hankel’stransform is defined as: F v ( s ) = H v [ f ( r )] = (cid:90) ∞ rf ( r ) J v ( sr ) dr, r ≥ , (1.6)where J v is the Bessel function of the first kind of order v with v ≥ − .In 1993, Watugala introduced a Laplace-like integral transform called the Sumuduintegral transform [27]. In recent years, Sumudu transform has been applied tomany real-life problems because of its scale and unit preserving properties ([28]-[31]). The mathematical definition of the Sumudu transform is given by: S [ f ( t )]( u ) = G ( u ) = 1 u (cid:90) ∞ exp (cid:18) − tu (cid:19) f ( t ) dt, (1.7)provided the integral exists for some u . Based on the basic idea of the Laplace andthe Sumudu integral transform, the Elzaki transform was proposed in 2011. TheElzaki transform is closely related with the Laplace transform, Sumudu transform,and the natural transform. Elzaki transform is defined as [32]: E [ f ( t )] = T ( u ) = u (cid:90) ∞ exp (cid:18) − tu (cid:19) f ( t ) dt, (1.8)provided the integral exists for some u .The natural transform [33] which is similar to Laplace and Sumudu integraltransform was introduced in 2008. In recent years, natural transform was success-fully applied to many applications (see [34, 35]). The natural transform is definedby the following integral: N + [ f ( t )]( s, u ) = R ( s, u ) = 1 u (cid:90) ∞ exp (cid:18) − stu (cid:19) f ( t ) dt, s > , u > , (1.9) EW INTEGRAL TRANSFORM FOR SOLVING DIFFERENTIAL EQUATIONS 3 provided the integral exists for some variables u and s . Recently, a new integraltransform called the M -transform which is also similar to natural transform isintroduced by Srivastava et al. in 2015. Mathematically speaking, M -transform isclosely connected with the well-known Laplace transform and the Sumudu integraltransform. M -transform was successfully applied to first order initial-boundaryvalue problem (see Srivastava et al. [36]). The M -transform is defined as: M ρ,m [ f ( t )]( u, v ) = (cid:90) ∞ exp ( − ut ) f ( vt )( t m + v m ) ρ dt, (1.10)( ρ ∈ C ; (cid:60) ( ρ ) ≥ , m ∈ Z + = 1 , , , · · · ) , where both u ∈ C and v ∈ R + are the M -transform variables.In 2013, Atangana and Kilicman introduced a novel integral transform calledthe Abdon-Kilicman integral transform [37] for solving some differential equationswith some kind of singularities. The novel integral transform is defined as: M n ( s ) = M n [ f ( x )]( s ) = (cid:90) ∞ x n exp ( − xs ) f ( x ) dx. (1.11)The Atangana-Kilicman integral becomes Laplace transform when n = 0. Recently,a Laplace-type integral transform called the Yang transform ([38]-[40]) for solvingsteady heat transfer problems was introduced in 2016. The integral transform isdefined as: Y [ φ ( τ )] = φ ( ω ) = (cid:90) ∞ exp (cid:18) − τω (cid:19) φ ( τ ) dτ, (1.12)provided the integral exists for some ω .Due to the rapid development in the physical science and engineering models,there are many other integral transforms in the literature. However, most of theexisting integral transforms have some limitations and cannot be used directly tosolved nonlinear problems or many complex mathematical models. As a result,many authors became highly interested to come up with the alternative approachfor solving many real-life problems. In 2016, Atangana and Alkaltani introduceda new double integral equation and their properties based on the Laplace trans-form and decomposition method. The double integral transform was successfullyapplied to second order partial differential equation with singularity called the two-dimensional Mboctara equation [41]. Recently, Eltayeb applied double Laplacedecomposition method to nonlinear partial differential equations [42]. In 2017, Bel-gacem el at. extended the applications of the natural and the Sumudu transformsto fractional diffusion and Stokes fluid flow realms [43].Motivated by the above-mentioned researches, in this paper we proposed aLaplace-type integral transform called Shehu transform for solving both ordinaryand partial differential equations. The Laplace-type integral transform convergesto Laplace transform when u = 1, and to Yang integral transform when s = 1.The proposed integral transform is successfully applied to both ordinary and par-tial differential equations. All the results obtained in the applications section caneasily be verified using the Laplace or Fourier integral transforms. Throughout thispaper, the Shehu transform is denoted by an operator S [ . ]. EW INTEGRAL TRANSFORM FOR SOLVING DIFFERENTIAL EQUATIONS 4 Main result
Definition 1.
The Shehu transform of the function v ( t ) of exponential order isdefined over the set of functions, A = (cid:110) v ( t ) : ∃ N, η , η > , | v ( t ) | < N exp (cid:16) | t | η i (cid:17) , if t ∈ ( − i × [0 , ∞ ) (cid:111) ,by the following integral S [ v ( t )] = V ( s, u ) = (cid:90) ∞ exp (cid:18) − stu (cid:19) v ( t ) dt = lim α →∞ (cid:90) α exp (cid:18) − stu (cid:19) v ( t ) dt ; s > , u > . (2.1)It converges if the limit of the integral exists, and diverges if not.The inverse Shehu transform is given by S − [ V ( s, u )] = v ( t ) , f or t ≥ . (2.2)Equivalently v ( t ) = S − [ V ( s, u )] = 12 πi (cid:90) α + i ∞ α − i ∞ u exp (cid:18) stu (cid:19) V ( s, u ) ds, (2.3)where s and u are the Shehu transform variables, and α is a real constant and theintegral in Equ.(2.3) is taken along s = α in the complex plane s = x + iy . Theorem 1.
The sufficient condition for the existence of Shehu trans-form . If the function v ( t ) is piecewise continues in every finite interval ≤ t ≤ β and of exponential order α for t > β . Then its Shehu transform V ( s, u ) exists. Proof.
For any positive number β , we algebraically deduce (cid:90) ∞ exp (cid:18) − stu (cid:19) v ( t ) dt = (cid:90) β exp (cid:18) − stu (cid:19) v ( t ) dt + (cid:90) ∞ β exp (cid:18) − stu (cid:19) v ( t ) dt. (2.4)Since the function v ( t ) is piecewise continues in every finite interval 0 ≤ t ≤ β , thenthe first integral on the right hand side exists. Besides, the second integral on theright hand side exists, since the function v ( t ) is of exponential order α for t > β .To verify this claim, we consider the following case (cid:12)(cid:12)(cid:12)(cid:12)(cid:90) ∞ β exp (cid:18) − stu (cid:19) v ( t ) dt (cid:12)(cid:12)(cid:12)(cid:12) ≤ (cid:90) ∞ β (cid:12)(cid:12)(cid:12)(cid:12) exp (cid:18) − stu (cid:19) v ( t ) (cid:12)(cid:12)(cid:12)(cid:12) dt ≤ (cid:90) ∞ exp (cid:18) − stu (cid:19) | v ( t ) | dt ≤ (cid:90) ∞ β exp (cid:18) − stu (cid:19) N exp ( αt ) dt = N (cid:90) ∞ β exp (cid:18) − ( s − αu ) tu (cid:19) dt = − uN ( s − αu ) lim γ →∞ (cid:20) exp (cid:18) − ( s − αu ) tu (cid:19)(cid:21) γ = uNs − αu . The proof is complete. (cid:3)
EW INTEGRAL TRANSFORM FOR SOLVING DIFFERENTIAL EQUATIONS 5
Property 1.
Linearity property of Shehu transform . Let the functions αv ( t ) and βw ( t ) be in set A, then ( αv ( t ) + βw ( t )) ∈ A, where α and β are nonzero arbi-trary constants, and S [ αv ( t ) + βw ( t )] = α S [ v ( t )] + β S [ w ( t )] . (2.5) Proof.
Using the Definition 1 of Shehu transform, we get S [ αv ( t ) + βw ( t )] = (cid:90) ∞ exp (cid:18) − stu (cid:19) ( αv ( t ) + βw ( t )) dt = (cid:90) ∞ exp (cid:18) − stu (cid:19) ( αv ( t )) dt + (cid:90) ∞ exp (cid:18) − stu (cid:19) ( βw ( t )) dt = α (cid:90) ∞ exp (cid:18) − stu (cid:19) v ( t ) dt + β (cid:90) ∞ exp (cid:18) − stu (cid:19) w ( t ) dt = αu (cid:90) ∞ exp ( − st ) v ( ut ) dt + βu (cid:90) ∞ exp ( − st ) w ( ut ) dt = α S [ v ( t )] + β S [ w ( t )] . The proof is complete. (cid:3)
In particular, using the Definition 1 and Property 1, we obtain S [3 cos( t ) + 5 sin(2 t )] = 3 S [cos( t )] + 5 S [sin(2 t )]= 3 uss + u + 5 u s + (2 u ) , see entries of table 1. Property 2.
Change of scale property of Shehu transform.
Let the function v ( βt ) be in set A, where β is an arbitrary constant. Then S [ v ( βt )] = uβ V (cid:18) sβ , u (cid:19) . (2.6) Proof.
Using the Definition 1 of Shehu transform, we deduce S [ v ( βt )] = (cid:90) ∞ exp (cid:18) − stu (cid:19) v ( βt ) dt (2.7) Substituting η = βt which implies t = ηβ and dt = dηβ in Equ.(2.7) yields S [ v ( βt )] = 1 β (cid:90) ∞ exp (cid:18) − sηuβ (cid:19) v ( η ) dη = 1 β (cid:90) ∞ exp (cid:18) − stuβ (cid:19) v ( t ) dt = uβ (cid:90) ∞ exp (cid:18) − stβ (cid:19) v ( ut ) dt = uβ V (cid:18) sβ , u (cid:19) . The proof is complete. (cid:3)
EW INTEGRAL TRANSFORM FOR SOLVING DIFFERENTIAL EQUATIONS 6
Theorem 2.
Derivative of Shehu transform.
If the function v ( n ) ( t ) is the nth derivative of the function v ( t ) ∈ A with respect to (cid:48) t (cid:48) , then its Shehu transform isdefined by S (cid:104) v ( n ) ( t ) (cid:105) = s n u n V ( s, u ) − n − (cid:88) k =0 (cid:16) su (cid:17) n − ( k +1) v ( k ) (0) . (2.8)When n=1, 2, and 3 in Equ. (2.8) above, we obtain the following derivatives withrespect to t . S [ v (cid:48) ( t )] = su V ( s, u ) − v (0) . (2.9) S [ v (cid:48)(cid:48) ( t )] = s u V ( s, u ) − su v (0) − v (cid:48) (0) . (2.10) S [ v (cid:48)(cid:48)(cid:48) ( t )] = s u V ( s, u ) − s u v (0) − su v (cid:48) (0) − v (cid:48)(cid:48) (0) . (2.11) Proof.
Now suppose Equ. (2.8) is true for n = k . Then using Equ. (2.9) and theinduction hypothesis, we deduce S (cid:104) ( v ( k ) ( t )) (cid:48) (cid:105) = su S (cid:104) v ( k ) ( t ) (cid:105) − v ( k ) (0)= su (cid:34) s k u k S [ v ( t )] − k − (cid:88) i =0 (cid:16) su (cid:17) k − ( i +1) v ( i ) (0) (cid:35) − v ( k ) (0)= (cid:16) su (cid:17) k +1 S [ v ( t )] − k (cid:88) i =0 (cid:16) su (cid:17) k − i v ( i ) (0) , which implies that Equ. (2.8) holds for n = k + 1. By induction hypothesis theproof is complete. (cid:3) The following important properties are obtain using the Leibniz’s rule S (cid:20) ∂v ( x, t ) ∂x (cid:21) = (cid:90) ∞ exp (cid:18) − stu (cid:19) ∂v ( x, t ) ∂x dt = ∂∂x (cid:90) ∞ exp (cid:18) − stu (cid:19) v ( x, t ) dt = ∂∂x [ V ( x, s, u )] ⇒ S (cid:20) ∂v ( x, t ) ∂x (cid:21) = ddx [ V ( x, s, u )] , S (cid:20) ∂ v ( x, t ) ∂x (cid:21) = (cid:90) ∞ exp (cid:18) − stu (cid:19) ∂ v ( x, t ) ∂x dt = ∂ ∂x (cid:90) ∞ exp (cid:18) − stu (cid:19) v ( x, t ) dt = ∂ ∂x [ V ( x, s, u )] ⇒ S (cid:20) ∂ v ( x, t ) ∂x (cid:21) = d dx [ V ( x, s, u )] , and S (cid:20) ∂ n v ( x, t ) ∂x n (cid:21) = (cid:90) ∞ exp (cid:18) − stu (cid:19) ∂ n v ( x, t ) ∂x n dt = ∂ n ∂x n (cid:90) ∞ exp (cid:18) − stu (cid:19) v ( x, t ) dt = ∂ n ∂x n [ V ( x, s, u )] ⇒ S (cid:20) ∂ n v ( x, t ) ∂x n (cid:21) = d n dx n [ V ( x, s, u )] . EW INTEGRAL TRANSFORM FOR SOLVING DIFFERENTIAL EQUATIONS 7 Some useful results of Shehu transform
Property 3.
Let the function v ( t ) = 1 be in set A. Then its Shehu transform isgiven by S [1] = us . (3.1) Proof.
Using Equ.(2.1), we deduce S [1] = (cid:90) ∞ exp (cid:18) − stu (cid:19) dt = − us lim γ →∞ (cid:20) exp (cid:18) − stu (cid:19)(cid:21) γ = us . This ends the proof. (cid:3)
Property 4.
Let the function v ( t ) = t be in set A. Then its Shehu transform isgiven by S [ t ] = u s . (3.2) Proof.
Using the Definition 1 of the Shehu transform and integration by parts, weget S [ t ] = (cid:90) ∞ t exp (cid:18) − stu (cid:19) dt = us lim γ →∞ (cid:20) t exp (cid:18) − stu (cid:19)(cid:21) γ + us (cid:90) ∞ exp (cid:18) − stu (cid:19) dt = − u s lim γ →∞ (cid:20) exp (cid:18) − stu (cid:19)(cid:21) γ = u s . Thus the proof ends. (cid:3)
Property 5.
Let the function v ( t ) = t n n ! n = 0 , , .. be in set A. Then its Shehutransform is given by S (cid:20) t n n ! (cid:21) = (cid:16) us (cid:17) n +1 . (3.3) Proof.
From the Definition 1 of the Shehu transform and integration by parts,we deduce S [ t n ] = (cid:90) ∞ t n exp (cid:18) − stu (cid:19) dt = us n (cid:90) ∞ t n − exp (cid:18) − stu (cid:19) dt = u s n ( n − (cid:90) ∞ t n − exp (cid:18) − stu (cid:19) dt = u s n ( n − n − (cid:90) ∞ t n − exp (cid:18) − stu (cid:19) dt = u s n ( n − n − n − (cid:90) ∞ t n − exp (cid:18) − stu (cid:19) dt = u s n ( n − n − n − n − (cid:90) ∞ t n − exp (cid:18) − stu (cid:19) dt = · · · = n ! (cid:16) us (cid:17) n +1 . The proof is completed. (cid:3)
Property 6.
Let the function v ( t ) = t n Γ( n +1) n = 0 , , , · · · be in set A. Then itsShehu transform is given by S (cid:20) t n Γ( n + 1) (cid:21) = (cid:16) us (cid:17) n +1 . (3.4) EW INTEGRAL TRANSFORM FOR SOLVING DIFFERENTIAL EQUATIONS 8
The proof of property 6 follows immediately from the previous property 5. (cid:3)
Property 7.
Let the function v ( t ) = exp( αt ) be in A. Then its Shehu transformis given by S [exp( αt )] = us − αu . (3.5) Proof.
Using Equ.(2.1), we get S [exp( αt )] = (cid:90) ∞ exp (cid:18) − ( s − αu ) tu (cid:19) dt = − us − αu lim γ →∞ (cid:20) exp (cid:18) − ( s − αu ) tu (cid:19)(cid:21) γ = us − αu . This ends the proof. (cid:3)
Property 8.
Let the function v ( t ) = t exp( αt ) be in set A. Then its Shehu trans-form is given by S [ t exp( αt )] = u ( s − αu ) . (3.6) Proof.
Using the Definition 1 of the Shehu transform and integration by parts,we get S [ t exp( αt )] = (cid:90) ∞ t exp (cid:18) − ( s − αu ) tu (cid:19) dt = − us − αu lim γ →∞ (cid:20) t exp (cid:18) − ( s − αu ) tu (cid:19)(cid:21) γ + us − αu (cid:90) ∞ exp (cid:18) − ( s − αu ) tu (cid:19) dt = − u ( s − αu ) lim γ →∞ (cid:20) exp (cid:18) − ( s − αu ) tu (cid:19)(cid:21) γ = u ( s − αu ) . The proof is complete. (cid:3)
Property 9.
Let the function v ( t ) = t n exp( αt ) n ! n = 0 , , , ... be in set A. Then itsShehu transform is given by S (cid:20) t n exp( αt ) n ! (cid:21) = u n +1 ( s − αu ) n +1 . (3.7) Proof.
Using the Definition 1 of the Shehu transform and integration by parts,we deduce S [ t n exp( αt )] = (cid:90) ∞ t n exp (cid:18) − ( s − αu ) tu (cid:19) dt = un ( s − αu ) (cid:90) ∞ t n − exp (cid:18) − ( s − αu ) tu (cid:19) dt = u n ( n − s − αu ) (cid:90) ∞ t n − exp (cid:18) − ( s − αu ) tu (cid:19) dt = · · · = n !( s − αu ) n +1 . Thus the proof is complete. (cid:3)
EW INTEGRAL TRANSFORM FOR SOLVING DIFFERENTIAL EQUATIONS 9
Property 10.
Let the function v ( t ) = t n Γ( n +1) exp( αt ) n = 0 , , , ... be in set A.Then its Shehu transform is given by S (cid:20) t n exp( αt )Γ( n + 1) (cid:21) = u n +1 ( s − αu ) n +1 . (3.8) The proof of Property 10 follows as a direct consequence of Property 9. (cid:3)
Property 11.
Let the function v ( t ) = sin ( αt ) be in set A. Then its Shehu trans-form is given by S [sin( αt )] = αu s + α u . (3.9) Proof.
Using the Definition 1 of the Shehu transform and integration by parts, weget S [sin( αt )] = (cid:90) ∞ exp (cid:18) − stu (cid:19) sin( αt ) dt = − us lim γ →∞ (cid:20) exp (cid:18) − stu (cid:19) sin( αt ) (cid:21) γ + uαs (cid:90) ∞ exp (cid:18) − stu (cid:19) cos( αt ) dt = − αu s lim γ →∞ (cid:20) exp (cid:18) − stu (cid:19) cos( αt ) (cid:21) γ − α u s (cid:90) ∞ exp (cid:18) − stu (cid:19) sin( αt ) dt = αu s − α u s (cid:90) ∞ exp (cid:18) − stu (cid:19) sin( αt ) dt. Simplifying the required integrals complete the proof of Property 11. (cid:3)
Property 12.
Let the function v ( t ) = cos( αt ) be in set A. Then its Shehu transformis given by S [cos( αt )] = uss + α u . (3.10) Proof.
Using the Definition 1 of the Shehu transform and integration by parts, wededuce S [cos( αt )] = (cid:90) ∞ exp (cid:18) − stu (cid:19) cos( αt ) dt = − us lim γ →∞ (cid:20) exp (cid:18) − stu (cid:19) cos( αt ) (cid:21) γ − αus (cid:90) ∞ exp (cid:18) − stu (cid:19) sin( αt ) dt = us − αu s lim γ →∞ (cid:20) exp (cid:18) − stu (cid:19) sin( αt ) (cid:21) γ − α u s (cid:90) ∞ exp (cid:18) − stu (cid:19) cos( αt ) dt = us − α u s (cid:90) ∞ exp (cid:18) − stu (cid:19) cos( αt ) dt. Simplifying the required integrals complete the proof of Property 12. (cid:3)
Property 13.
Let the function v ( t ) = sinh( αt ) α be in set A. Then its Shehu transformis given by S (cid:20) sinh( αt ) α (cid:21) = u s − α u . (3.11) EW INTEGRAL TRANSFORM FOR SOLVING DIFFERENTIAL EQUATIONS 10
Proof.
From the Definition 1 of the Shehu transform and integration by parts, weget S [sinh( αt )] = (cid:90) ∞ exp (cid:18) − stu (cid:19) sinh( αt ) dt = − us lim γ →∞ (cid:20) exp (cid:18) − stu (cid:19) sinh( αt ) (cid:21) γ + uαs (cid:90) ∞ exp (cid:18) − stu (cid:19) cosh( αt ) dt = − αu s lim γ →∞ (cid:20) exp (cid:18) − stu (cid:19) cos( αt ) (cid:21) γ + α u s (cid:90) ∞ exp (cid:18) − stu (cid:19) sinh( αt ) dt = αu s + α u s (cid:90) ∞ exp (cid:18) − stu (cid:19) sinh( αt ) dt. Simplifying the required integrals complete the proof of Property 13. (cid:3)
Property 14.
Let the function v ( t ) = cosh( αt ) be in set A. Then its Shehu trans-form is given by S [cosh( αt )] = uss − α u . (3.12) Proof.
Applying the Definition 1 of the Shehu transform and integration by parts,we get S [cosh( αt )] = (cid:90) ∞ exp (cid:18) − stu (cid:19) cosh( αt ) dt = − us lim γ →∞ (cid:20) exp (cid:18) − stu (cid:19) cos( αt ) (cid:21) γ + αus (cid:90) ∞ exp (cid:18) − stu (cid:19) sinh( αt ) dt = us − αu s lim γ →∞ (cid:20) exp (cid:18) − stu (cid:19) sinh( αt ) (cid:21) γ + α u s (cid:90) ∞ exp (cid:18) − stu (cid:19) cos( αt ) dt = us + α u s (cid:90) ∞ exp (cid:18) − stu (cid:19) cosh( αt ) dt. Collecting the required integrals complete the proof of Property 14. (cid:3)
Property 15.
Let the function exp( βt ) sin( αt ) α be in set A. Then its Shehu transformis given by S (cid:20) exp ( βt ) sin( αt ) α (cid:21) = u ( s − βu ) + α u . (3.13) EW INTEGRAL TRANSFORM FOR SOLVING DIFFERENTIAL EQUATIONS 11
Proof.
Using the Definition 1 of the Shehu transform and integration by parts, wededuce S [exp ( βt ) sin( αt )] = (cid:90) ∞ exp (cid:18) − ( s − βu ) u t (cid:19) sin( αt ) dt = − u ( s − βu ) lim γ →∞ (cid:20) exp (cid:18) − ( s − βu ) u t (cid:19) sin( αt ) dt (cid:21) γ + uαs − βu (cid:90) ∞ exp (cid:18) − ( s − βu ) u t (cid:19) cos( αt ) dt = − u α ( s − βu ) lim γ →∞ (cid:20) exp (cid:18) − ( s − βu ) u t (cid:19) cos( αt ) dt (cid:21) γ − αu α ( s − βu ) (cid:90) ∞ exp (cid:18) − ( s − βu ) u t (cid:19) sin( αt ) dt = u α ( s − βu ) − u α ( s − βu ) (cid:90) ∞ exp (cid:18) − ( s − βu ) u t (cid:19) sin( αt ) dt. Simplifying the required integrals complete the proof of property 15. This ends theproof. (cid:3)
Property 16.
Let the function exp ( βt ) cos( αt ) be in set A. Then its Shehu trans-form is given by S [exp ( βt ) cos( αt )] = u ( s − αu )( s − βu ) + α u . (3.14) Proof.
Applying the Definition 1 of the Shehu transform and integration by parts,we get S [exp ( βt ) cos( αt )] = (cid:90) ∞ exp (cid:18) − ( s − βu ) u t (cid:19) cos( αt ) dt = − us − βu lim γ →∞ (cid:20) exp (cid:18) − ( s − βu ) u t (cid:19) cos( αt ) (cid:21) γ + αus − βu (cid:90) ∞ exp (cid:18) − ( s − βu ) u t (cid:19) sin( αt ) dt = us − βu + αus − βu (cid:90) ∞ exp (cid:18) − ( s − βu ) u t (cid:19) sin( αt ) dt = us − βu + αu ( s − αu ) lim γ →∞ (cid:20) exp (cid:18) − ( s − βu ) u t (cid:19) sin( αt ) (cid:21) γ − α u ( s − βu ) (cid:90) ∞ exp (cid:18) − ( s − βu ) u t (cid:19) cos( αt ) dt = us − βu − α u ( s − βu ) (cid:90) ∞ exp (cid:18) − ( s − βu ) u t (cid:19) cos( αt ) dt. Simplifying the required integrals complete the proof of property 16. (cid:3)
Property 17.
Let the function exp( βt ) − exp( αt ) β − α be in set A. Then its Shehu trans-form is given by S (cid:20) exp ( αt ) β − α (cid:21) = u ( s − αu )( s − βu ) . (3.15) EW INTEGRAL TRANSFORM FOR SOLVING DIFFERENTIAL EQUATIONS 12
Proof.
Using the definition of Shehu transform, we get S (cid:20) exp ( αt ) β − α (cid:21) = uβ − α (cid:90) ∞ exp (cid:18) − stu (cid:19) (exp( βt ) − exp ( αt )) dt = 1 β − α (cid:90) ∞ e ( βu − s ) u t dt − β − α (cid:90) ∞ exp (cid:18) ( αu − s ) tu (cid:19) dt = u ( β − α )( βu − s ) lim γ →∞ (cid:20) exp (cid:18) − ( s − βu ) tu (cid:19)(cid:21) γ − u ( β − α )( αu − s ) lim γ →∞ (cid:20) exp (cid:18) − ( s − βu ) tu (cid:19)(cid:21) γ = − u ( β − α )( βu − s ) + u ( β − α )( αu − s )= − u ( αu − s ) + u ( βu − s )( β − α )( αu − s )( βu − s ) = u ( s − αu )( s − βu ) . The proof is complete. (cid:3)
Property 18.
Let the function β exp( βt ) − α exp( αt ) β − α be in set A. Then its Shehu trans-form is given by: S (cid:20) β exp ( βt ) − α exp ( αt ) β − α (cid:21) = us ( s − αu )( s − βu ) . (3.16) Proof:
Using the definition of Shehu transform, we get S (cid:20) β exp ( βt ) − α exp ( αt ) β − α (cid:21) = 1 β − α (cid:90) ∞ exp (cid:18) − stu (cid:19) ( β exp ( βt ) − α exp ( αt )) dt = ββ − α (cid:90) ∞ exp (cid:18) ( βu − s ) u t (cid:19) dt − αβ − α (cid:90) ∞ exp (cid:18) ( αu − s ) tu (cid:19) dt = uβ ( β − α )( βu − s ) lim γ →∞ (cid:20) exp (cid:18) − ( s − βu ) tu (cid:19)(cid:21) γ − uα ( β − α )( αu − s ) lim γ →∞ (cid:20) exp (cid:18) − ( s − αu ) tu (cid:19)(cid:21) γ = − uβ ( β − α )( βu − s ) + uα ( β − α )( αu − s )= − uβ ( αu − s ) + uα ( βu − s )( β − α )( αu − s )( βu − s ) = us ( s − αu )( s − βu ) . This ends the proof. (cid:3)
More properties of the Shehu transform and their converges to the natural trans-form, the Sumudu transform, and the Laplace transform are presented in table 1.The comprehensive summary of Shehu transform properties are presented in table2. 4.
Applications
In this section, the applications of the proposed transform are presented. Thesimplicity, efficiency and high accuracy of the Shehu transform are clearly illus-trated.
EW INTEGRAL TRANSFORM FOR SOLVING DIFFERENTIAL EQUATIONS 13
Example 1.
Consider the following first order ordinary differential equation dv ( t ) dt + v ( t ) = 0 , (4.1) subject to the initial condition v (0) = 1 . (4.2) Applying the Shehu transform on both sides of Equ. (4.1), we get su V ( s, u ) − v (0) + V ( s, u ) = 0 . (4.3)Substituting the given initial condition and simplifying, we deduce V ( s, u ) = us + u (4.4)Taking the inverse Shehu transform of Equ. (4.4), yields v ( t ) = exp( − t ) . (4.5) Example 2.
Consider the following second order ordinary differential equation d v ( t ) dt + dv ( t ) dt = 1 (4.6) subject to the initial conditions v (0) = 0 , dv (0) dt = 0 . (4.7) Applying the Shehu transform on both sides of Equ. (4.6), we obtain s u V ( s, u ) − su v (0) − v (cid:48) (0) + su V ( s, u ) − v (0) = us . (4.8)Substituting the given initial conditions and simplifying, we deduce V ( s, u ) = − us + u s + us + u . (4.9)Taking the inverse Shehu transform of Equ. (4.9), we get v ( t ) = − t + exp( − t ) . (4.10) Example 3.
Consider the following second nonhomogeneous order ordinary differ-ential equation d v ( t ) dt − dv ( t ) dt + 2 v ( t ) = exp(3 t ) (4.11) subject to the initial conditions v (0) = 1 , dv (0) dt = 0 . (4.12) Applying the Shehu transform on both sides of Equ. (4.11), yields s u V ( s, u ) − su v (0) − v (cid:48) (0) − (cid:16) su V ( s, u ) − v (0) (cid:17) + 2 V ( s, u ) = us − u . (4.13)Substituting the given initial conditions and simplifying, we obtain V ( s, u ) = 52 u ( s − u ) − us − u + 12 u ( s − u ) . (4.14)Taking the inverse Shehu transform of Equ. (4.14), we get v ( t ) = 52 exp( t ) − t ) + 12 exp(3 t ) . (4.15) EW INTEGRAL TRANSFORM FOR SOLVING DIFFERENTIAL EQUATIONS 14
Example 4.
Consider the following ordinary differential equation d v ( t ) dt + 2 dv ( t ) dt + 5 v ( t ) = exp( − t ) sin( t ) (4.16) subject to the initial conditions v (0) = 0 , dv (0) dt = 1 . (4.17) Applying the Shehu transform on both sides of Equ. (4.16), we get s u V ( s, u ) − su v (0) − v (cid:48) (0) + 2 (cid:16) su V ( s, u ) − su v (0) (cid:17) + 5 V ( s, u ) = u ( s + u ) + u (4.18)Substituting the given initial conditions and simplifying, we get V ( s, u ) = 13 u (( s + u ) + u ) + 23 u (( s + u ) + (2 u ) ) (4.19)Taking the inverse Shehu transform of Equ. (4.19), we get v ( t ) = 13 exp( − t ) sin( t ) + 23 exp( − t ) sin(2 t ) . (4.20) Example 5.
Consider the following homogeneous partial differential equation ∂v ( x, t ) ∂t = ∂ v ( x, t ) ∂x (4.21) subject to the boundary and initial conditions v (0 , t ) = 0 , v (1 , t ) = 0 , v ( x,
0) = 3 sin (2 πx ) . (4.22) Applying the Shehu transform on both sides of Equ. (4.21), we get su V ( x, s, u ) − v ( x,
0) = d V ( x, s, u ) dx . (4.23)Substituting the given initial condition and simplifying, we get d V ( x, s, u ) dx − su V ( x, s, u ) = − sin (2 πx ) . (4.24)The general solution of Equ. (4.24) can be written as V ( x, s, u ) = V h ( x, s, u ) + V p ( x, s, u ) , (4.25)where V h ( x, s, u ) is the solution of the homogeneous part which is given by V h ( x, s, u ) = α exp (cid:18)(cid:114) su x (cid:19) + α exp (cid:18) − (cid:114) su x (cid:19) , (4.26)and V p ( x, s, u ) is the solution of the nonhomogeneous part which is given by V p ( x, s, u ) = β sin (2 πx ) + β cos (2 πx ) . (4.27)Applying the boundary conditions on Equ. (4.26), we get α + α = 0 and α exp (cid:18)(cid:114) su (cid:19) + α exp (cid:18) − (cid:114) su (cid:19) = 0 ⇒ V h ( x, s, u ) = 0 , EW INTEGRAL TRANSFORM FOR SOLVING DIFFERENTIAL EQUATIONS 15 since α = α = 0.Using the method of undetermined coefficients on the nonhomogeneous part, weget V p ( x, s, u ) = 3 us + 4 π u sin(2 πx ) , (4.28)Since, β = us +4 π u , and β = 0.Then Equ. (4.25) will become V ( x, s, u ) = 3 us + 4 π u sin(2 πx ) , (4.29)Taking the inverse Shehu transform of Equ. (4.29), we get v ( x, t ) = 3 exp( − π t ) sin(2 πx ) . (4.30) Figure 1.
3D and 2D surfaces of the analytical solution of Equ. (4.21) in theranges − < x <
1, and − < t <
1, when t = 1. Example 6.
Consider the following nonhomogeneous partial differential equation ∂ v ( x, t ) ∂t = β ∂ v ( x, t ) ∂x + sin( πx ) (4.31) subject to the boundary and initial conditions v (0 , t ) = 0 , v (1 , t ) = 0 , v ( x,
0) = 0 , ∂v ( x, ∂t = 0 , β = 1 . (4.32) Applying the Shehu transform on both sides of Equ. (4.31), we get s u V ( x, s, u ) − su v ( x, − v (cid:48) ( x,
0) = d V ( x, s, u ) dx + us sin( πx ) . (4.33)Substituting the given initial condition and simplifying, we get d V ( x, s, u ) dx − s u V ( x, s, u ) = − us sin( πx ) . (4.34)The general solution of Equ. (4.34) can be written as V ( x, s, u ) = V h ( x, s, u ) + V p ( x, s, u ) , (4.35)where V h ( x, s, u ) is the solution of the homogeneous part which is given by V h ( x, s, u ) = λ exp (cid:16) su x (cid:17) + λ exp (cid:16) − su x (cid:17) , (4.36)and V p ( x, s, u ) is the solution of the nonhomogeneous part which is given by V p ( x, s, u ) = η sin( πx ) + η cos( πx ) . (4.37) EW INTEGRAL TRANSFORM FOR SOLVING DIFFERENTIAL EQUATIONS 16
Applying the boundary conditions on Equ. (4.36), we deduce λ + λ = 0 and λ exp (cid:16) su (cid:17) + λ exp (cid:16) − su (cid:17) = 0 ⇒ V h ( x, s, u ) = 0 , since λ = λ = 0.Using the method of undetermined coefficients on the nonhomogeneous part, weget V p ( x, s, u ) = 1 π (cid:18) us − uss + u π (cid:19) sin( πx ) , (4.38)since, η = u s ( s + u π ) = 1 π (cid:18) us − uss + u π (cid:19) , and η = 0 . Then Equ. (4.35) will becomes V ( x, s, u ) = 1 π (cid:18) us − uss + u π (cid:19) sin( πx ) . (4.39)Taking the inverse Shehu transform of Equ. (4.39), we get v ( x, t ) = 1 π (1 − cos( πt )) sin( πx ) . (4.40) Figure 2.
3D and 2D surfaces of the analytical solution of Equ. (4.31) in theranges − < x <
1, and − < t < Conclusion
We introduced an efficient Laplace-type integral transform called the Shehu trans-form for solving both ordinary and partial differential equations. We presented itsexistence and inverse transform. We presented some useful properties and theirapplications for solving ordinary and partial differential equations. We provide acomprehensive list of the Laplace transform, Sumudu transform, and the naturaltransform in table 1 to show their mutual relationship with the Shehu transform.Finally, based on the mathematical formulations, simplicity and the findings of theproposed integral transform, we conclude that it is highly efficient because of thefollowing advantages: • It is a generalization of the Laplace and the Sumudu integral transforms. • Its visualization is easier than the Sumudu transform, the natural trans-form, and the Elzaki transform.
EW INTEGRAL TRANSFORM FOR SOLVING DIFFERENTIAL EQUATIONS 17 • The Laplace-type integral transform become Laplace transform when thevariable u = 1 and the Yang integral transform when the variable s = 1. • It can easily be applied directly to some class of ordinary and the partialdifferential equations as demonstrated in the application section. • For advanced research in physical science and engineering, the proposedintegral transform can be considered a stepping-stone to the Sumudu trans-form, the natural transform, the Elzaki transform, and the Laplace trans-form. 6.
Acknowledgements
The authors are highly grateful to the editor’s and the anonymous referees’ fortheir useful comments and suggestions in this paper. This research is partiallysupported by the National Natural Science Foundations of China under GrantsNo. (11571206). The first author also acknowledges the financial support ofChina Scholarship Council (CSC) in Shandong University with grand (CSC No:2017GXZ025381).
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Appendix
Table 1:
Here we present a comprehensive list of the Shehu transform of some specialfunctions and their relationship with the natural transform N [ v ( t )], the Sumudutransform S [ v ( t )], and the Laplace transform.S.NO. v ( t ) S [ v ( t )] N [ v ( t )] S [ v ( t )] £ [ v ( t )]1 1 us s s t u s us u s α ( t )) us − αu s − αu − αu s − α sin( αt ) α u s + α u us + α u u α u s + α αt ) uss + α u ss + α u α u ss + α EW INTEGRAL TRANSFORM FOR SOLVING DIFFERENTIAL EQUATIONS 20 αt uss − u ss − u − u ss − t n n ! n = 0 , , ... (cid:0) us (cid:1) n +1 u n s n +1 u n s n +1 t n Γ( n +1) n = 0 , , , ... (cid:0) us (cid:1) n +1 u n s n +1 u n s n +1 t ) uss + u ss + u u s +1
10 sin( t ) u s + u us + u u u s +1 sinh ( αt ) α u s − α u αus − α u αu − α u αs − α
12 cosh( αt ) uss − α u ss − α u − α u ss − α
13 exp( βt ) cosh ( αt ) u ( s − βu )( s − βu ) − α u s − βu ( s − βu ) − α u − βu ( s − βu ) − α u s − β ( s − βu ) − α exp( βt ) sinh( αt ) α u ( s − βu ) − α u u ( s − βu ) − α u u (1 − βu ) − α u s − β ) − α t sin( αt )2 α u s ( s + α u ) u s ( s + α u ) u (1+ α u ) s ( s + α ) t cos( αt ) u ( s − α u ) ( s + α u ) u ( s − α u ) ( s + α u ) u (1 − α u ) (1+ α u ) ( s − α ) ( s + α ) sin( αt )+ αt cos( αt )2 α u s ( s + α u ) us ( s + α u ) u (1+ α u ) s ( s + α )
18 cos αt − αt sin( αt )2 us ( s + α u ) s ( s + α u ) α u ) s ( s + α ) sin( αt ) − αt cos( αt )2 α u ( s + α u ) u ( s + α u ) u (1+ α u ) s + α ) t sinh( αt ) + t cosh( αt ) u ( s − αu ) u ( s − αu ) u (1 − αu ) s − α ) t sinh( αt )2 α u s ( s − α u ) u s ( s − α u ) u (1 − α u ) s ( s − α ) Si ( αt ) (Sine integral) us tan − (cid:0) αus (cid:1) s tan − (cid:0) αus (cid:1) tan − (cid:16) u √ α (cid:17) s tan − (cid:0) αs (cid:1) Ci ( αt ) (Cosine integral) − u s log (cid:16) s + α α (cid:17) − s log (cid:16) s + α u α u (cid:17) − log (cid:16) α u +1 α u (cid:17) − s log (cid:16) s + α α (cid:17) Ei ( αt ) (Exp. integral) − us log (cid:0) αu − sαu (cid:1) − s log (cid:0) αu − sαu (cid:1) log (cid:0) αu − αu (cid:1) − s log (cid:0) α − sα (cid:1) (3 − α t ) sin( αt ) − αt cos( αt )8 α u ( s + α u ) u ( s + α u ) u (1+ α u ) s + α ) (3 − α t ) sin( αt )+5 αt cos( αt )8 α u s ( s + α u ) us ( s + α u ) u (1+ α u ) s ( s + α ) (8 − α t ) cos( αt ) − αt sin( αt )8 us ( s + α u ) s ( s + α u ) α u ) s ( s + α ) t sin( αt )2 α u (3 s − α u )( s + α u ) u (3 s − α u )( s + α u ) u ( − α u )(1+ α u ) (3 s − α )( s + α ) t cos( αt )2 u ( s − α u s )( s + α u ) u ( s − α u s )( s + α u ) u (1 − α u )(1+ α u ) ( s − α s )( s + α ) t sin( αt )24 α su ( s − αu ) ( s + α u ) su ( s − αu ) ( s + α u ) u (1 − αu ) (1+ α u ) s ( s − α ) ( s + α ) exp( αt ) − exp( βt ) α − β α (cid:54) = β u ( s − αu )( s − βu ) u ( s − αu )( s − βu ) u (1 − βu )(1 − αu ) 1( s − β )( s − α ) EW INTEGRAL TRANSFORM FOR SOLVING DIFFERENTIAL EQUATIONS 21 α exp( αt ) − β exp( βt ) α − β α (cid:54) = β us ( s − βu )( s − αu ) s ( s − βu )( s − αu ) 1(1 − βu )(1 − αu ) s ( s − β )( s − α ) I ( αt ) u √ s − α u √ s − α u √ − α u √ s − α δ ( t − α ) u exp (cid:0) − αsu (cid:1) u exp (cid:0) − αsu (cid:1) u exp (cid:0) − αu (cid:1) exp( − αs )35 J ( αt ) u √ s + α u √ s + α u √ α u √ s + α Table 2:
General properties of Shehu transformS.NO. Definition/Property S [ v ( t )] = V ( s, u ) Transforms1 Definition S [ v ( t )] (cid:82) ∞ exp (cid:0) − stu (cid:1) v ( t ) dt ; s > , u >
02 Inverse v ( t ) = S − [ V ( s, u )] πi (cid:82) α + i ∞ α − i ∞ u exp (cid:0) stu (cid:1) V ( s, u ) ds S [ αv ( t ) + βw ( t )] α S [ v ( t )] + β S [ w ( t )]4 Change of scale S [ v ( αt )] uα V (cid:0) sα , u (cid:1) S [ v (cid:48) ( t )] su V ( s, u ) − v (0) S [ v (cid:48)(cid:48) ( t )] s u V ( s, u ) − su v (0) − v (cid:48) (0) S [ v (cid:48)(cid:48)(cid:48) ( t )] s u V ( s, u ) − s u v (0) − su v (cid:48) (0) − v (cid:48)(cid:48) (0)... S (cid:104) v ( n ) ( t ) (cid:105) s n u n V ( s, u ) − (cid:80) n − k =0 (cid:0) su (cid:1) n − ( k +1) EW INTEGRAL TRANSFORM FOR SOLVING DIFFERENTIAL EQUATIONS 22
Table 3:
Summary of some integral transform and their definitionsS.No. Integral transform Definition1 Laplace transform £ [ f ( t )] = F ( s ) = (cid:82) ∞ exp ( − st ) f ( t ) dt (cid:122) [ f ( t )] = f ( ω ) = √ π (cid:82) ∞−∞ exp ( − iωt ) f ( t ) dt M [ f ( s ); s ] = f ∗ ( s ) = (cid:82) ∞ x s − f ( x ) dx F v ( s ) = H v [ f ( r )] = (cid:82) ∞ rf ( r ) J v ( sr ) dr, r ≥
05 Sumudu transform S [ f ( t )] = G ( u ) = u (cid:82) ∞ exp (cid:0) − tu (cid:1) f ( t ) dt f C ( p ) = p (cid:82) ∞ exp ( − pt ) f ( t ) dt , t ≥
07 Atangana-Kilicman transform M n ( s ) = M n [ f ( x )]( s ) = (cid:82) ∞ x n exp ( − xs ) f ( x ) dx E [ f ( t )] = T ( u ) = u (cid:82) ∞ exp (cid:0) − tu (cid:1) f ( t ) dt Y [ φ ( τ )] = φ ( ω ) = (cid:82) ∞ exp (cid:0) − τω (cid:1) φ ( τ ) dτ
10 natural transform N + [ f ( t )] = R ( s, u ) = u (cid:82) ∞ exp (cid:0) − stu (cid:1) f ( t ) dt, s > , u >