Abstract
In this article, we define a new fractional technique which is known as generalized proportional fractional (GPF) integral in the sense of another function  The authors prove several inequalities for newly defined GPF-integral with respect to another function  Our consequences will give noted outcomes for a suitable variation to the GPF-integral in the sense of another function  and the proportionality index . Furthermore, we present the application of the novel operator with several integral inequalities. A few new properties are exhibited, and the numerical approximation of these new operators is introduced with certain utilities to real-world problems.
    1. Introduction
A revolution via the discipline of fractional calculus was perceived, whereas the conventional was conjointly brought up because the classical calculus becomes stretched out to the conception of non-local operators. Fractional calculus was popularized and implemented in numerous areas of science, technology, and engineering as a mathematical model. The idea of this new calculus was implemented in many diversified disciplines previously with outstanding achievements completed in the frame of new discoveries and posted academic articles, see [,,,] and the references therein.
Numerous distinguished generalized fractional integral operators consist of the Hadamard operator, Erdélyi–Kober operators, the Saigo operator, the Gaussian hypergeometric operator, the Marichev–Saigo–Maeda fractional integral operator and so on; out of these, the Riemann–Liouville (RL) fractional integral operator was extensively utilized by analysts in the literature as well as applications. For more information, see [,,,]. Almeida [] expounded -Caputo derivative in the sense of another function  and Kilbas et al. [] explored the concept of RL-fractional integrals in the sense of another function  The attractors with numerical simulations work for varying values and this permits the readers to choose the most appropriate operator for demonstrating the issue under investigation. In addition, as a result of its effortlessness in utilities, analysts have given much consideration to presently determined fractional operators without singular kernels [,,,,,]. Later on, numerous articles considering these sorts of fractional operators turned out to be noteworthy.
In [], Jarad et al. presented the concept of generalized proportional-integral operators which was utilized to characterize some probability density functions and has intriguing applications in statistics (also see [,,]).
Following this tendency, we introduce another fractional operator in more general form which is known as the generalized proportional fractional operator in the sense of another function . These kinds of speculations elevate future studies to investigate novel concepts to modify the fractional operators and attain fractional integral inequalities within such generalized fractional operators (see Remark 1 below). It is noted that GPF-integrals are used to manipulate statistical learning and integrodifferential equations, see [,,,] and the references therein.
Inequalities and their utilities assume a crucial job in the literature of applied mathematics. The assortment of distinct kinds of classical variants and their modifications were built up by using the classical fractional operators and their developments in [,,,,,]. Adopting this propensity, we give a modified version for the most distinguished Grüss type inequality [] and some other related variants in the frame of the GPF-integral in the sense of another function  that could be increasingly effective and more applicable than the existing ones. More accurately, Grüss inequality can be described as follows:
Definition 1. 
([]) Let two positive functions  (set of real numbers) such that  and  for all . Then
      
        
      
      
      
      
    where the constant  is sharp and .
The aforementioned inequality sincerely associates the integral of the product two functions with the product of their integrals. Inequality (1) is a tremendous mechanism for investigating numerous scientific areas of research comprising engineering, fluid dynamics, bio-sciences, chaos, meteorology, vibration analysis, biochemistry, aerodynamics, and many more. There was a constant development of enthusiasm for such an area of research so as to address the issues of different utilizations of these variants, see [,,,,,,,].
The principal purpose of this article is to derive novel integral inequalities including a Grüss type inequality and several other related variants via GPF in the sense of another function , by using Young’s, weighted arithmetic and geometric mean inequalities. Interestingly, the special cases of presented results are generalized RL-fractional integral and RL-fractional integral inequalities. Therefore, it is important to summarize the study of fractional integrals.
2. Prelude
In this segment, we give some significant ideas from fractional calculus utilized in our consequent discourse. The fundamental specifics are presented in the monograph by Kilbas et al. []. Throughout the paper, for the results concerning [], it is assumed that all functions are integrable in the Riemann sense.
Definition 2. 
([,]) A function  is said to be in  space if
      
        
      
      
      
      
    
For 
      
        
      
      
      
      
    
Definition 3. 
([]) Let  and Ψ be an increasing and positive monotone function on  and also derivative  is continuous on  and  The space  of those real-valued Lebesgue measurable functions  on  for which
      
        
      
      
      
      
    and for the case 
      
        
      
      
      
      
    
Specifically, when  the space  coinsides with the -space and also if we choose  the space  coincides with -space.
Now, we present a new fractional operator which is known as the GPF-integral operator of a function in the sense of another function 
Definition 4. 
Let  there is an increasing, positive monotone function Ψ defined on  having continuous derivative  on  with  Then the left-sided and right-sided GPF-integral operator of a function  in the sense of another function Ψ of order  are stated as:
      
        
      
      
      
      
    and
      
        
      
      
      
      
    where the proportionality index  and  is the Gamma function.
Remark 1. 
- (1)
 - (2)
 - (3)
 - (4)
 - (5)
 - (6)
 
Definition 5. 
Let  and there is an increasing, positive monotone function Ψ defined on  having continuous derivative  on  with  Then the one-sided GPF-integral operator of a function  in the sense of another function Ψ of order  and proportionality index  is stated as:
      
        
      
      
      
      
    
For the suitability of inaugurating our consequences, we prove the following semigroup and linearity property for the newly introduced operator.
Theorem 1. 
(Semigroup Property) Let  be a GPF-integral operator in the sense of another function  Then for  and  we have:
      
        
      
      
      
      
    
Proof.  
Consider
      
        
      
      
      
      
    
Now, interchanging the order of integration and changing variables defined by  in the inner integral
      
        
      
      
      
      
    
        where  is the well known Euler Beta function. □
Remark 2. 
If we choose  along with  then (17) becomes the result of [].
Suppose a bounded interval , such that . The operators  and  link the function  and  to each GPF integrable function  in the sense of another function  on  In this manner, these are linear operators, which is demonstrated in the following hypothesis.
Theorem 2. 
(linearity) The operators  and  are linear operators on . That is, characterize
      
        
      
      
      
      
    then
      
        
      
      
      
      
    
For all  and 
Proof.  
The proof is simple, consider
      
        
      
      
      
      
    
Analogously
      
        
      
      
      
      
     □
3. Main Results
This section is devoted to establishing generalizations of some classical inequalities by employing GPF integral with respect to another function  defined in (16).
Theorem 3. 
For  and let  Suppose that there is an increasing, positive monotone function Ψ defined on  having continuous derivative  on  with  Moreover, one assumes that there exist two integrable functions  on  such that
      
        
      
      
      
      
    
Then, for  one has
      
        
      
      
      
      
    
Proof.  
From (18), for all  one has
        
      
        
      
      
      
      
    
Therefore,
      
        
      
      
      
      
    
Taking product on both sides of (21) by  and integrating the estimate with respect to  from 0 to  one obtains
      
        
      
      
      
      
    
        and arrives at
        
      
        
      
      
      
      
    
Taking product on both sides of (23) by  and integrating the estimate with respect to  from 0 to  we have
      
        
      
      
      
      
    
Hence, we deduce inequality (20) as required. This concludes the proof. □
Some special cases can be derived immediately from Theorem 3.
 Choosing  then we attain a new result for GPF-integrals.
Corollary 1. 
For  and let  Assume that there exist two integrable functions  on  such that
      
        
      
      
      
      
    Then, for  we get
      
        
      
      
      
      
    
 Letting  then we attain a result for generalized RL-fractional integrals.
Corollary 2. 
Let , and there is an increasing and positive monotone function Ψ defined on  having continuous derivative  on  with  Moreover, one assumes that there exist two integrable functions  on  such that
      
        
      
      
      
      
    
Then, for  we get
      
        
      
      
      
      
    which is proposed by Kacar et al. [].
 Choosing  along with  then we attain a result for RL-fractional integrals.
Corollary 3. 
Let  Assume that there exist two integrable functions  on  such that
      
        
      
      
      
      
    
Then, for  we get
      
        
      
      
      
      
    which is proposed by Tariboon et al. [].
Theorem 4. 
For  and let  and  be two positive functions on  and there is an increasing, positive monotone function Ψ defined on  having continuous derivative  on  with  Suppose that (18) holds and moreover one assumes that there exist  and  integrable functions on  such that
      
        
      
      
      
      
    
Then, for  the following inequalities hold:
      
        
      
      
      
      
    
Proof.  
Therefore,
        
      
        
      
      
      
      
    
Taking product on both sides of (28) by  and integrating the estimate with respect to  from 0 to  we have
      
        
      
      
      
      
    
Then we have
      
        
      
      
      
      
    
Again, taking product on both sides of (30) by  and integrating the estimate with respect to  from 0 to  we have
      
        
      
      
      
      
    
It follows that
      
        
      
      
      
      
    
        where we get the desired inequality .
We can prove other inequalities by taking into account the following indentities, respectively:
      
        
      
      
      
      
    
      
        
      
      
      
      
    
      
        
      
      
      
      
     □
As a special case of Theorem 4, we have the following corollaries.
 Letting  then we get a new result for GPF-integrals:
Corollary 4. 
For  and let  and  be two positive functions on  Suppose that (18) holds and moreover one assumes that there exist  and  integrable functions on  such that
      
        
      
      
      
      
    
Then, for  the following inequalities hold:
      
        
      
      
      
      
    
 Letting  then we attain a result for generalized RL-fractional integral.
Corollary 5. 
let  and  be two positive functions on  and there is an increasing, positive monotone function Ψ defined on  having continuous derivative on  with  Suppose that (18) holds and moreover one assumes that there exist  and  integrable functions on  such that
      
        
      
      
      
      
    
Then, for  the following inequalities hold:
      
        
      
      
      
      
    which is proposed by Kacar et al. [].
 Letting  along with  then we attain a result for RL-fractional integrals:
Corollary 6. 
let  Suppose that (18) holds and moreover one assumes that there exist  and  integrable functions on  such that
      
        
      
      
      
      
    
Then, for  the following inequalities hold:
      
        
      
      
      
      
    which is proposed by Tariboon et al. [].
4. Some other Fractional Integral Inequalities for GPF-Integral in the Sense of Another Function
Theorem 5. 
For  and let  and  be two positive functions on  and there is an increasing, positive monotone function Ψ defined on  having continuous derivative  on  with   satisfying  Then, for  one has
      
        
      
      
      
      
    
Proof.  
According to the well-known Young’s inequality []:
      
        
      
      
      
      
    
        setting  and  we have
      
        
      
      
      
      
    
Taking product on both sides of (36) by  and integrating the estimate with respect to  from 0 to  we have
      
        
      
      
      
      
    
        we get
      
        
      
      
      
      
    
Taking product on both sides of (36) by  and integrating the estimate with respect to  from 0 to  we have
      
        
      
      
      
      
    
        consequently, we get
      
        
      
      
      
      
    
        which implies . The remaining variants can be derived by adpoting the same technique and accompaying the selection of parameters in Young inequality.
      
        
      
      
      
      
    
Repeating the foregoing argument, we obtain  □
 Letting  then we attain a result for generalized RL-fractional integral.
Corollary 7. 
Let  and  be two positive functions on  and there is an increasing, positive monotone function Ψ defined on  having continuous derivative  on  with  satisfying  Then, for  we get
      
        
      
      
      
      
    
Theorem 6. 
For  and let  and  be two positive functions on  and there is an increasing, positive monotone function Ψ defined on  having continuous derivative  on  with  and  satisfying  Then, for  one has
      
        
      
      
      
      
    
Proof.  
From the well-known weighted  inequality
      
        
      
      
      
      
    
        by setting  and  we have
      
        
      
      
      
      
    
Taking product on both sides of (43) by  and integrating the estimate with respect to  and  from 0 to  respectively, we have
      
        
      
      
      
      
    
        we conclude that
      
        
      
      
      
      
    
        which implies  The remaining inequalities can be proved by adopting the same technique by the accompanying selection of parameters in  inequality.
      
        
      
      
      
      
     □
 Letting  then we attain a result for generalized RL-fractional integrals:
Corollary 8. 
Let  and  be two positive functions on  and there is an increasing, positive monotone function Ψ defined on  having continuous derivative  on  with  and  satisfying  Then, for  we get
      
        
      
      
      
      
    
Theorem 7. 
Let  and  be two positive functions on  and there is an increasing, positive monotone function Ψ defined on  having continuous derivative  on  with  and  satisfying  Let
      
        
      
      
      
      
    
Then, for  one has the following inequalities:
      
        
      
      
      
      
    
Proof.  
Taking product on both sides of (48) by  and integrating the estimate with respect to  from 0 to  we have
      
        
      
      
      
      
    
        which implies that
      
        
      
      
      
      
    
        on the other hand, it follows from  and
      
        
      
      
      
      
    
        that
      
        
      
      
      
      
    
5. Conclusions
In this article, we derived several theorems by newly defined generalized proportional fractional integral operators with respect to another function  having proportionality index  The analogous versions of the Grüss inequality and several other associated variants were derived by employing GPF in the sense of another function . Moreover, we took a few specific instances of these hypotheses, by utilizing Remark 1. Since the GPF is an association of the diverse kind of operators, we can determine the various types of variants by choosing the qualities pertinent to the limitations and the proportionality index . These results can be applied in convex analysis, optimization, integrodifferential equation, and also different areas of pure and applied sciences. Finally, the GPF in the sense of another function subject to the nonlocal exponential kernel provided the outline for obtaining the results for exponential and normal distribution in statistical theory. Note that the outcomes in this paper are like hypothetically surely understood proliferation properties of fractional Schrödinger equation [,]. Besides, our outcomes are practically identical to equality-time evenness in a fractional Schrödinger equation [] and proliferation elements of light beam in a fractional Schrödinger equation []. Indeed, the work set up in the given arrangement is new and contributes suggestively to the study of integrodifferential and difference equations.
Author Contributions
All authors contributed substantially to the research. Conceptualization: S.R.; methodology, S.R.; software, S.R., F.J.; validation, F.J. and M.A.N.; formal analysis, F.J.; investigation, M.A.N., F.J. and Y.-M.C.; resources, M.A.N; data curation, H.K.; writing, original draft preparation, S.R., H.K.; writing, review and editing, S.R., H.K. and M.A.N.; supervision, S.R. and Y.-M.C.; project administration, Y.-M.C.; funding acquisition, Y.-M.C.
Funding
This research was funded by the Natural Science Foundation of China grant number 61673169.
Conflicts of Interest
The authors declare no conflict of interest.
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