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. 2016 May 21;5(1):683. doi: 10.1186/s40064-016-2299-x

Note on generalized Mittag-Leffler function

Rachana Desai 1, I A Salehbhai 2, A K Shukla 3,
PMCID: PMC4899392  PMID: 27350918

Abstract

The present paper deals with the study of a generalized Mittag-Leffler function and associated fractional operator. The operator has been discussed in the space of Lebesgue measurable functions. The composition with Riemann–Liouville fractional integration operator has been obtained.

Keywords: Generalized Mittag-Leffler function, Fractional Calculus

Background

The well-known Mittag-Leffler function Eα(z) named after its originator, the Swedish mathematician Gosta Mittag-Leffler (1846–1927), is defined by (Mittag-Leffler 1903)

Eα(z)=n=0znΓ(αn+1);zis a complex variable andReα0. 1

The Mittag–Leffler function naturally occurs as the solution of fractional order differential equations. The various generalization of Mittag–Leffler function have been defined and studied by different authors.

Shukla and Prajapati (2007) introduced its generalization Eα,βγ,q(z), this is defined as

Eα,βγ,q(z)=n=0(γ)qnΓ(αn+β)znn!; 2

for α,β,γC; Reα>0,Reβ>0,Reγ>0,Reδ>0, q(0,1)N, and (γ)qn=Γ(γ+qn)Γ(γ) denotes the generalized Pochhammer symbol.

Further, the generalization of (2) is also given by Khan and Ahmed (2013), as follows:

Eα,β,υ,σ,δ,pμ,ρ,γ,q(z)=n=0(μ)ρn(γ)qnznΓ(αn+β)(υ)σn(δ)pn, 3

where α,β,γ,δ,μ,υC; p,q,ρ,σ>0;qRe(α)+p; ρReσ+p; qReσ+p; ρ,q(0,1)N and minReα,Reβ,Reγ,Reδ,Reμ,Reυ>0.

Here, the convergence conditions of (3) have been modified, which was given by Khan and Ahmed (2013).

The following well-known notations and definitions have been used:

Let L(a,b) (Kilbas et al. 2004) be a set of all Lebesgue measurable real or complex valued functions f(x) on [a,b] i.e.

L(a,b)=f:f1abf(t)dt< 4

Let f(x)L(a,b), μC(Re(μ)>0) then the Riemann–Liouville left-sided fractional integrals of order μ (Miller and Ross 1993) is defined as

aIxμf(x)=Ia+μf(x)=1Γ(μ)axf(t)(x-t)1-μdt(x>a) 5

and the R–L right-sided fractional integral of order μ is defined as

bIxμfx=Ib-μfx=1Γ(μ)xbf(t)(t-x)1-μdt(x<b) 6

Miller and Ross (1993) defined the following:

If μ,α,βC, Re(μ)>0; n=[Re(μ)]+1; Re(β)>0 then

Ia+μ[(t-a)β-1](x)=Γ(β)Γ(μ+β)(x-a)μ+β-1 7

and

(Da+αf)(x)=ddxn(Ia+n-αf)(x). 8

Khan and Ahmed (2013) proved the following result.

If α,β,γ,δ,μ,υ,ρ,σC; p,q>0; qRe(α)+p and

Reα>0,Reβ>0,Reγ>0,Reδ>0,Reμ>0,Reυ>0,Reρ>0,Reσ>0

then for mN,

ddzmzβ-1Eα,β,υ,σ,δ,pμ,ρ,γ,q(wzα)=zβ-m-1Eα,β,υ,σ,δ,pμ,ρ,γ,q(wzα);Reβ-m>0. 9

In continuation of study, in this paper we give the operator associated with Eα,β,υ,σ,δ,pμ,ρ,γ,q(z) as follows:

Let f(x)L(a,b), define

Eα,β,υ,σ,δ,p;w;a+μ,ρ,γ,qf(x)=axx-tβ-1Eα,β,υ,σ,δ,pμ,ρ,γ,qwx-tαftdt;x>a, 10

where α,β,γ,δ,μ,υC; p,q,ρ,σ>0; qRe(α)+p; ρReσ+p; qReσ+p and minReα,Reβ,Reγ,Reδ,Reμ,Reυ>0.

Main results

Using the definition (4), one can easily prove following lemma.

Lemma 1

Ifα,β,γ,δ,μ,υ,ρ,σC; p,q>0; qRe(α)+p; x>a; aR+=[0,)and minReα,Reβ,Reγ,Reδ,Reμ,Reυ,Reρ,Reσ>0,then

Eα,β,υ,σ,δ,pμ,ρ,γ,q(atα)=βEα,β+1,υ,σ,δ,pμ,ρ,γ,qatα+αtEα,β+1,υ,σ,δ,pμ,ρ,γ,qatα 11

Theorem 1

LetaR+=[0,). Letα,β,γ,δ,μ,υ,ρ,σC; p,q>0 ; qRe(α)+pandminReα,Reβ,Reγ,Reδ,Reμ,Reυ,Reρ,Reσ>0,x>a.Then

Ia+r(t-a)β-1Eα,β,υ,σ,δ,pμ,ρ,γ,q{w(t-a)α}(x)=(x-a)r+β-1Eα,β+r,υ,σ,δ,pμ,ρ,γ,q[w(x-a)α 12
Da+r(t-a)β-1Eα,β,υ,σ,δ,pμ,ρ,γ,q{w(t-a)α}(x)=(x-a)β-r-1Eα,β-r,υ,σ,δ,pμ,ρ,γ,q[w(x-a)α 13

Proof

Using definitions (3) and (5) and further simplification gives

Ia+r(t-a)β-1Eα,β,υ,σ,δ,pμ,ρ,γ,q{w(t-a)α}(x)=n=0(μ)ρn(γ)qnΓ(αn+β)wn(υ)σn(δ)pnIa+r[(t-a)αn+β-1](x)=n=0(μ)ρn(γ)qnΓ(αn+β)wn(υ)σn(δ)pnΓ(αn+β)Γ(αn+β+r)(x-a)αn+β+r-1=(x-a)r+β-1n=0(μ)ρn(γ)qnΓ(αn+β+r)[w(x-a)α](υ)σn(δ)pnn=(x-a)r+β-1Eα,β+r,υ,σ,δ,pμ,ρ,γ,q[w(x-a)α.

This completes the proof of (12).□

To prove (13), we use definitions (8) and further simplification gives

Da+r(t-a)β-1Eα,β,υ,σ,δ,pμ,ρ,γ,q{w(t-a)α}(x)=ddxnIa+n-r[(t-a)β-1Eα,β,υ,σ,δ,pμ,ρ,γ,q{w(t-a)α}](x),

On applying (12) with replacement of r by n-r, the above equation reduces to

=ddxn(x-a)β+n-r-1Eα,β+n-r,υ,σ,δ,pμ,ρ,γ,q{w(x-a)α},

From (9), we get

=(x-a)β+n-r-1-nEα,β+n-r-n,υ,σ,δ,pμ,ρ,γ,q{w(x-a)α}=(x-a)β-r-1Eα,β-r,υ,σ,δ,pμ,ρ,γ,q[w(x-a)α].

Theorem 2

LetaR+=[0,),α,β,γ,δ,μ,υ,ρ,σC; p,q>0andqRe(α)+pandminReα,Reβ,Reγ,Reδ,Reμ,Reυ,Reρ,Reσ>0x>a.Then

Eα,β,υ,σ,δ,p;w;a+μ,ρ,γ,q(t-a)r-1(x)=(x-a)β+r-1Γ(r)Eα,β+r,υ,σ,δ,pμ,ρ,γ,qw(x-a)α. 14

Proof

Taking f(t)=(t-a)r-1 in (10), we get

Eα,β,υ,σ,δ,p;w;a+μ,ρ,γ,q(t-a)r-1(x)=ax(x-t)β-1Eα,β,υ,σ,δ,pμ,ρ,γ,q[w(x-t)α](t-a)r-1dt=n=0(μ)ρn(γ)qnΓ(αn+β)wn(υ)σn(δ)pnax(x-t)αn+β-1(t-a)r-1dt,

Replacing t by a+(x-a)t and simplifying the above equation

=n=0(μ)ρn(γ)qnΓ(αn+β)wn(υ)σn(δ)pn(x-a)αn+β+r-1B(αn+β,r)

and further simplification of above equation gives the proof of Theorem 2.

Theorem 3

LetaR+=[0,),α,β,γ,δ,μ,υ,ρ,σC; p,q>0andqRe(α)+pandminReα,Reβ,Reγ,Reδ,Reμ,Reυ,Reρ,Reσ>0,b>a., Then the operatorEα,β,υ,σ,δ,p;w;a+μ,ρ,γ,qis bounded onL(a,b)and

Eα,β,υ,σ,δ,p;w;a+μ,ρ,γ,qf1Bf1, 15

where

B=(b-a)Re(β)n=0(μ)ρn(γ)qn[Re(α)n+Re(β)]Γ(αn+β)w(b-a)Re(α)n(υ)σn(δ)pn. 16

Proof

On using the definition (10) and applying Dirichlet’s formula (Samko et al. 1993), we have

Eα,β,υ,σ,δ,p;w;a+μ,ρ,γ,qf1=abax(x-t)β-1Eα,β,υ,σ,δ,pμ,ρ,γ,q[w(x-t)α]f(t)dtdxabtb(x-t)Re(β)-1Eα,β,υ,σ,δ,pμ,ρ,γ,q[w(x-t)α]dxf(t)dt,

Taking u=x-t in inner integral, this yields

Eα,β,υ,σ,δ,p;w;a+μ,ρ,γ,qf1ab0b-tuRe(β)-1Eα,β,υ,σ,δ,pμ,ρ,γ,q[wuα]duf(t)dtabn=0(μ)ρn(γ)qnΓ(αn+β)wn(υ)σn(δ)pnuRe(α)n+Re(β)Re(α)n+Re(β)0b-af(t)dt=(b-a)Re(β)n=0(μ)ρn(γ)qnΓ(αn+β)wn(υ)σn(δ)pn(b-a)Re(α)n[Re(α)n+Re(β)]abf(t)dt

This completes the proof.□

Theorem 4

(Composition with Riemann–Liouville fractional integration operator) Letα,β,γ,δ,μ,υ,ρ,σC; p,q>0; qRe(α)+p; b>aandminReα,Reβ,Reγ,Reδ,Reμ,Reυ,Reρ,Reσ>0.Then the relation

Ia+rEα,β,υ,σ,δ,p;w;a+μ,ρ,γ,qfEα,β+r,υ,σ,δ,p;w;a+μ,ρ,γ,qfEα,β,υ,σ,δ,p;w;a+μ,ρ,γ,qIa+rf 17

holds for any summable functionfL(a,b).

Proof

From (10) and (5), we get

(Ia+rEα,β,υ,σ,δ,p;w;a+μ,ρ,γ,qf)(x)=1Γ(r)axau(x-u)r-1(u-t)β-1Eα,β,υ,σ,δ,pμ,ρ,γ,q[w(u-t)α]f(t)dtdu

Applying Dirichlet’s formula (Samko et al. 1993), we get

=ax1Γ(r)tx(x-u)r-1(u-t)β-1Eα,β,υ,σ,δ,pμ,ρ,γ,q[w(u-t)α]duf(t)dt

Substituting u-t=τ in the above equation, we get

=ax1Γ(r)0x-t(x-t-τ)r-1τβ-1Eα,β,υ,σ,δ,pμ,ρ,γ,q[wτα]dτf(t)dt

Again using (5), this equation becomes

=axI0+μτβ-1Eα,βγ,q(wτα)(x-t)f(t)dt,

Applying (12), this yields

=ax(x-t)β+r-1Eα,β+r,υ,σ,δ,pμ,ρ,γ,q[w(x-t)α]f(t)dt,

Using (10), we get

=(Eα,β+r,υ,σ,δ,p;w;a+μ,ρ,γ,qf)(x).

The other equality can also be proved in the similar way.

Theorem 5

Letα,β,γ,δ,μ,υ,ρ,σC; p,q>0; qRe(α)+p; b>aandminReα,Reβ,Reγ,Reδ,Reμ,Reυ,Reρ,Reσ>0.Then the relation

Da+rEα,β,υ,σ,δ,p;w;a+μ,ρ,γ,qfEα,β-r,υ,σ,δ,p;w;a+μ,ρ,γ,qf 18

holds for any continuous functionfC[a,b].

Proof

From (8), we have

Da+rEα,β,υ,σ,δ,p;w;a+μ,ρ,γ,qf(x)=ddxnIa+n-rEα,β,υ,σ,δ,p;w;a+μ,ρ,γ,qf(x)

Again using Theorem 4 and definition (10),

=ddxnax(x-t)β+n-r-1Eα,β+n-r,υ,σ,δ,pμ,ρ,γ,q[w(x-t)α]f(t)dt 19

The integrand in the above equation is continuous function on [a,b], here we take

ddxaxh(x,t)dt=axxh(x,t)dt+h(x,x) 20

From (19) and (20), we get

Da+rEα,β,υ,σ,δ,p;w;a+μ,ρ,γ,qf(x)=ddxn-1ax(x-t)β+n-r-2Eα,β+n-r-1,υ,σ,δ,pμ,ρ,γ,q[w(x-t)α]f(t)dt

Applying same procedures as above, this led the proof of the theorem. This is easy to prove by using mathematical induction method also.

Theorem 6

LetaR+=[0,),α,β,γ,δ,μ,υ,ρ,σC; p,q>0;qRe(α)+pandminReα,Reβ,Reγ,Reδ,Reμ,Reυ,Reρ,Reσ>0,x>a.Then

I0+rtβ-1Eα,β,υ,σ,δ,pμ,ρ,γ,q{atα}(x)=xr+β-1Eα,β+r,υ,σ,δ,pμ,ρ,γ,q[axα] 21

Proof

We have

I0+rtβ-1Eα,β,υ,σ,δ,pμ,ρ,γ,q{atα}(x)=n=0(μ)ρn(γ)qnΓ(αn+β)an(υ)σn(δ)pnI0+r[tαn+β-1](x)=n=0(μ)ρn(γ)qnΓ(αn+β)an(υ)σn(δ)pnΓ(αn+β)Γ(αn+β+r)(x)αn+β+r-1=xr+β-1n=0(μ)ρn(γ)qnΓ(αn+β+μ)[axα]n(υ)σn(δ)pn=xr+β-1Eα,β+r,υ,σ,δ,pμ,ρ,γ,q[axα].

This completes the proof.□

Corollary 1

Ifα,β,γ,δ,μ,υ,ρ,σC; p,q>0andqRe(α)+px>a; minReα,Reβ,Reγ,Reδ,Reμ,Reυ,Reρ,Reσ>0,aR+=[0,). LetI0+rbe the left-sided operator of Riemann–Liouville fractional integral. Then

I0+rtβ-1Eα,β,υ,σ,δ,pμ,ρ,γ,q{atα}(x)=xr+β-1{(β+r)Eα,β+r+1,υ,σ,δ,pμ,ρ,γ,q+xddxEα,β+r+1,υ,σ,δ,pμ,ρ,γ,q(axα)} 22

Proof is very obvious from Lemma 1 and Theorem 6.

Theorem 7

LetaR+=[0,), α,β,γ,δ,μ,υ,ρ,σC; p,q>0;qRe(α)+pandminReα,Reβ,Reγ,Reδ,Reμ,Reυ,Reρ,Reσ>0,x>a,I-rbe the right-sided operator of Riemann–Liouville fractional integral. Then

I-r[t-r-βEα,β,υ,σ,δ,pμ,ρ,γ,q{at-α}(x)=x-βEα,β+r,υ,σ,δ,pμ,ρ,γ,q[ax-α]

Proof

Let

I-r[t-r-βEα,β,υ,σ,δ,pμ,ρ,γ,q{at-α}(x)=1Γ(r)x(t-x)r-1t-r-βn=0(μ)ρn(γ)qn(at-α)nΓ(αn+β)(υ)σn(δ)pndt

On changing the order of the summation and integration then afterward applying beta function, this gives

=x-βn=0(μ)ρn(γ)qn(ax-α)nΓ(αn+β+r)(υ)σn(δ)pn=x-βEα,β+r,υ,σ,δ,pμ,ρ,γ,q{ax-α}

Corollary 2

Ifα,β,γ,δ,μ,υ,ρ,σC; p,q>0andqRe(α)+p;x>a;minReα,Reβ,Reγ,Reδ,Reμ,Reυ,Reρ,Reσ>0,aR+=[0,). LetI-rbe the right-sided operator of Riemann–Liouville fractional integral. Then

I-r[t-r-βEα,β,υ,σ,δ,pμ,ρ,γ,q{at-α}(x)=x-r-β{(β+r)Eα,β+r+1,υ,σ,δ,pμ,ρ,γ,q+xddxEα,β+r+1,υ,σ,δ,pμ,ρ,γ,q(ax-α)} 23

Conclusion

In this paper, we proved some properties of generalized Mittag-Leffler functions and also used the fractional calculus approach to prove Theorems 4, 5, 6 and 7.

Authors’ contributions

The authors contributed equally and significantly in writing this article. All authors read and approved the final manuscript.

Competing interests

The authors declare that they have no competing interests.

Contributor Information

Rachana Desai, Email: rachana.132@gmail.com.

I. A. Salehbhai, Email: ibrahimmaths@gmail.com

A. K. Shukla, Email: ajayshukla2@rediffmail.com

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