On Complex Intuitionistic Fuzzy Soft Sets with Distance Measures and Entropies

. We introduce the concept of complex intuitionistic fuzzy soft sets which is parametric in nature. However, the theory of complex fuzzy sets and complex intuitionistic fuzzy sets are independent of the parametrization tools. Some real life problems, for example, multicriteria decision making problems, involve the parametrization tools. In order to get their new entropies, some important properties and operations on the complex intuitionistic fuzzy soft sets have also been discussed. On the basis of some well-known distance measures, some new distance measures for the complex intuitionistic fuzzy soft sets have also been obtained. Further, we have established correspondence between the proposed entropies and the distance measures of complex intuitionistic fuzzy soft sets.


Introduction
Ramot et al. [1,2] introduced a new innovative concept of complex fuzzy set (CFS), where the membership function  instead of being a real valued function with the range of [0, 1] is replaced by a complex-valued function of the form   () ⋅  Ω  () ( = √ −1), where   () is a real valued function such that   () ∈ [0, 1] and Ω  () is a periodic function.The key feature of complex fuzzy sets is the presence of phase and its membership.This gives those complex fuzzy sets wavelike properties which could result in constructive and destructive interference depending on the phase value.Several examples are given in [2], which demonstrate the utility of these complex fuzzy sets.They also defined several important operations such as complement, union, and intersection and discussed fuzzy relations for such complex fuzzy sets.On the other hand, Ma et al. [3] used the complex fuzzy set to represent the information with uncertainty and periodicity, where they introduced a product-sum aggregation operator based prediction (PSAOP) method to find the solution of the multiple periodic factor prediction (MPFP) problems.Further, Chen et al. [4] proposed a neurofuzzy system architecture to implement the complex fuzzy rule as a practical application of the concept of complex fuzzy logic.
Intuitionistic fuzzy set (IFS), introduced by Atanassov [5], is a controlling tool to deal with vagueness and uncertainty.A prominent characteristic of IFS is that it assigns to each element a membership degree and a nonmembership degree with certain amount of hesitation degree.Atanassov [6,7] and many other researchers [8,9] studied different properties of IFSs in decision making problems, particularly in the case of medical diagnosis, sales analysis, new product marketing, financial services, and so forth.Alkouri and Salleh [10] introduced the concept of complex intuitionistic fuzzy set (CIFS) to represent the information which is happening repeatedly over a period of time.Further, as an application, Alkouri and Salleh [11] presented an example of suppler selection model which is based on the distance measure of complex intuitionistic fuzzy sets.
Molodtsov [12] pointed out that the important existing theories, namely, probability theory, fuzzy set theory, intuitionistic fuzzy set theory, rough set theory, and so forth, which can be considered as mathematical tools for dealing with uncertainties, have their own difficulties.The inadequacy of the parametrization tools of these theories makes them very limited and difficult.In order to overcome the above-stated difficulties, Molodtsov [12] introduced the concept of soft sets for dealing with uncertainties in 2 Journal of Mathematics parameterized form.Later on Maji et al. [13][14][15][16][17] extended soft sets to fuzzy soft sets and intuitionistic fuzzy soft sets.In 2005, Pei and Miao [18] and Chen et al. [19] have studied and extended the work of Maji et al. [13,14].Also, Majumdar and Samanta [20] have further generalized the concept of fuzzy soft sets.
In the present paper, we studied some fundamentals of soft set theory, fuzzy soft set theory, intuitionistic fuzzy soft sets, complex fuzzy sets, complex intuitionistic fuzzy sets, and some of their operations in Section 2. In Section 3, we introduced the concept of complex intuitionistic fuzzy soft sets (CIFSSs) along with their basic operations.New distance measures for CIFSSs have been obtained on the basis of some well-known distance measures and a general way to find the entropies of complex intuitionistic fuzzy soft sets has also been proposed in Section 4.An application in the area of multicriteria decision making problem on the basis of the proposed CIFSSs has also been suggested in Section 5. Finally, the paper has been concluded in Section 6.

Preliminaries
In this section, we present some basic definitions of the soft set, fuzzy soft set, intuitionistic fuzzy soft set, complex fuzzy soft set, and some operations on them which are well known in literature [1,2,12,15,16,21].
Definition 1 (see [12]).Let  be the universal set and let  be the set of parameters under consideration.Let P() denote the power set of .A soft set may be represented by the set of ordered pairs as where  is a mapping given by In other words, the soft set is a parameterized family of subsets of the universe .For each  ∈ , () may be considered as a set of -elements or as a set of -approximate elements of the soft set ⟨, ⟩.
Definition 2 (see [16]).Let  be the universal set and let  be the set of parameters under consideration.Let IFS() denote the set of all intuitionistic fuzzy subset of .An intuitionistic fuzzy soft set F may be represented by the set of ordered pairs as where F is a mapping given by F :  → IFS() such that Definition 3 (see [16,21]).Suppose that ⟨ F, ⟩ and ⟨ G, ⟩ are two intuitionistic fuzzy soft sets over a universal set . Then in view of the above definition, the following operations have been defined as follows.
Let CFS() be the set of all complex fuzzy sets on .The complex fuzzy set  may be represented as the set of ordered pairs: where By definition, the values of   () may receive all the values lying within the unit circle in the complex plane and are of the form where   is a real valued function such that   () ∈ [0, 1] and Ω  is a periodic function whose periodic law and principal period are, respectively, 2 and 0 ≤   () ≤ 2; that is, where   () is the principal argument.
Definition 5 (see [2]).Let  and  be two complex fuzzy sets on , and   () =   ()⋅   () and   () =   ()⋅   () are their membership functions, respectively.Then the following operations have been defined as follows: (a) union: where the ⬦ and * are -norm and -norm operators, respectively.It remains to define  ∪ () and  ∩ () for which the following axioms have to be followed.
In some cases, it may be required that V also satisfies the following axioms: (i) (continuity): V is a continuous function; The following are several possibilities for calculation of  ∪ () and  ∩ (), which, if combined with an appropriate function for determining  ∪ () and  ∩ (), satisfies the axiomatic requirements given in the above definitions.
Let  be a complex fuzzy set on  with the membership function   () =   () ⋅    () .The complex fuzzy complement of , denoted by , is specified by a function Ramot et al. [1] obtained several possible methods for calculating the membership phase of complex fuzzy complement,   ().For example,   () is defined as   () =   (); also   () may be defined by the relation   () = 2 −   (), where Zhang et al. [22] used this relation to define the complement for the phase component; also the rotation of   () by  radians may be a good method to calculate the complement for a phase term as   () =  +   ().
Alkouri and Salleh [10,11] gave the generalization of complex fuzzy set to the complex intuitionistic fuzzy set by adding the nonmembership term to the definition of CFS.The ranges of values are extended to the unit circle in complex plane for both membership and nonmembership functions instead of [0, 1] as in the conventional intuitionistic fuzzy sets.
Definition 7 (see [10,11]).A complex intuitionistic fuzzy set Ã, defined on a universal set , is characterized by the membership and nonmembership functions  Ã() and ] Ã(), respectively, which assign to each element  ∈  a complex-valued grade of membership and nonmembership in Ã.
Let CIFS() be the set of all complex intuitionistic fuzzy sets on .The complex intuitionistic fuzzy set Ã may be represented as the set of triplets where By definition, the values of  Ã(), ] Ã() and their sum all are lying within the unit circle in the complex plane and are of the form belong to (0, 2].

Complex Intuitionistic Fuzzy Soft Sets
The concept of soft set theory [12] has been used as a generic mathematical tool for dealing with uncertainty.However, in literature, it has been pointed out that the classical soft sets are not appropriate to deal with imprecise and fuzzy parameters.
In order to handle such information, the concept of fuzzy soft sets, intuitionistic fuzzy soft sets, and interval valued fuzzy soft sets have been laid down.In this section, we extend and introduce the concept of complex intuitionistic fuzzy soft set (CIFSS) with some important operations and properties.
Definition 8. Let  be universal set and let  be the set of parameters under consideration.Let CIFS() denote the set of all complex intuitionistic fuzzy subset of .A complex intuitionistic fuzzy soft set (CIFSS) may be represented by the set of ordered pairs as where Definition 9. Suppose that ⟨ F, ⟩ and ⟨ G, ⟩ are two CIFSSs over the universal set . Then in view of the above definition, one defines the following operations as follows.
(3) ( F, )  = ( F , ¬), where F : ¬ → IFS() is mapping given by In order to propose the intuitionistic entropy of complex intuitionistic fuzzy soft sets, we need to introduce some important properties of complex intuitionistic fuzzy soft sets.Definition 10.Let  be the set of parameters and suppose that ⟨ F, ⟩ and ⟨ G, ⟩ are two complex intuitionistic fuzzy soft sets over the universal set , and then one says that ⟨ G, ⟩ is a sharpened version of ⟨ F, ⟩; that is, ⟨ F, ⟩ ⪯ ⟨ G, ⟩ if and only if where The proposed operator   defined in Definition 11 is to assign a complex intuitionistic fuzzy soft set to a complex fuzzy soft set.The following theorem provides the properties of the operator   .

Distance Measures and Entropies of Complex Intuitionistic Fuzzy Soft Set
Based on various well-known distance functions, we introduce some distance measures between complex intuitionistic fuzzy soft sets and propose a general way to find the entropies of complex intuitionistic fuzzy soft set.We also give the structure of intuitionistic entropy of complex intuitionistic fuzzy soft sets by extending the structure of intuitionistic entropy on intuitionistic fuzzy soft sets [21].

Distance Measures between Complex Intuitionistic Fuzzy
Soft Sets.The axiomatic definition of the distance measure between complex intuitionistic fuzzy soft sets has been reframed and proposed as follows.
Definition 13.Suppose that  = ⟨ F, ⟩ and ξ = ⟨ G, ⟩ are two complex intuitionistic fuzzy soft sets over the universal set .

Entropies on Complex Intuitionistic Fuzzy Soft Sets.
Here, we present the axiomatic definition for the entropy of complex intuitionistic fuzzy soft sets.The following conditions give the intuitive idea for the degree of fuzziness of a complex intuitionistic fuzzy soft set, that is, for the entropy of a complex intuitionistic fuzzy soft set.
(i) It will be null when the complex intuitionistic fuzzy soft set is a complex fuzzy soft set.
(ii) It will be maximum if the complex intuitionistic fuzzy soft set is completely intuitionistic.
(iii) An intuitionistic entropy of a complex intuitionistic fuzzy soft set will be equal to its complement.
(iv) If the degree of membership and the degree of nonmembership of each element increase, the sum will do so as well, and therefore this complex intuitionistic fuzzy soft set becomes less fuzzy, and therefore the entropy should decrease.
In view of the above-stated points and the definition of entropy for an intuitionistic fuzzy soft set given in [21], we propose the following definition for the entropy of a complex intuitionistic fuzzy soft set.(iii) P3 (symmetry): () = (  ), for all  ∈ CIFSS(); Similar to the entropy of an intuitionistic fuzzy soft set [21], we deduce the following property from the property P2 of Definition 14.   ∈  such that  F(  ) (  ) ̸ = 0 and ] F(  ) (  ) ̸ = 0, where 0 ≤  ≤  and 0 ≤  ≤ .We construct the following complex intuitionistic fuzzy soft set:
Thus,  satisfies property P4 of Definition 14.Therefore,  is an intuitionistic entropy of complex intuitionistic fuzzy soft set.
Burillo and Bustince [23] gave some expressions for intuitionistic entropy of intuitionistic fuzzy soft sets.Jiang et al. [21] extended these expressions for intuitionistic entropy of intuitionistic fuzzy soft sets.On similar pattern, we are extending these expressions for intuitionistic entropy of complex intuitionistic fuzzy soft sets.
Let  = ⟨ F, ⟩ = [  ] × ∈ CIFSS().It is easy to verify that the following expressions are the intuitionistic entropies of : In the following definition, we introduce a function from CIFSS() to R + , which is an extension of the  , function from IFSS() to R + given in [21], which is also an extension of the  ,  -function from FSS() to R + given in [23].
Definition 17.Let ,   : [0, 1] → [0, 1] be such that if  +  ≤ 1, then () +   () ≤ 1, with ,  ∈ [0, 1].One defines function  ,  (⋅) of the complex intuitionistic fuzzy soft set  = ⟨ F, ⟩ = [  ] × ∈ CIFSS() to R + as follows: Thus, we have It may be noted that there are  ,  -functions which are not intuitionistic entropies; for example, On the other hand, it may also be easily verified that there are entropies which are not  ,  -functions; for example, Also, there are entropies which are also  ,  -functions; for example, Next, we introduce a property which defines entropies in a general way as follows.
We denote  ,  -function as  , -function if  =   .The following theorem characterizes the intuitionistic entropy of complex intuitionistic fuzzy soft sets in a general way.

Making problems
Suppose that a car dealer  decides to purchase cars from a car company .The car company provides some information to the car dealer on four different models of cars with different manufacturing dates for each model.So, the car dealer  wants to select four models, say, Car1, Car2, Car3, and Car4, with its manufacturing date simultaneously.Suppose that a team of experts (decision makers) agreed that five parameters should be considered in the selection process and they can be reliability, maximum payload, purchasing cost, maximum speed, and durability.It may be noted that the parameters may get affected and altered if the manufacturing date is different for a particular model of car.The decision made by the expert team will also depend on the knowledge and experience of its members.The best way to represent this kind of information may be by using CIFSS, in which, for each car model, the experts have different opinions and mentalities.For instance, suppose that at least 60% of experts believe that Car1 is suitable on the first parameter and not more than 15% of the experts believe that Car1 is poor on the first parameter.
In this way, we can calculate the amplitude terms for both membership and nonmembership functions of CIFSS.The phase terms that represent the manufacturing date for the first parameter of Car1 can be calculated as follows: whether at least 70% of experts believe that the production date of Car1 is suitable at the first parameter and not more than 20% of them believe that the production date of Car1 is poor.Therefore, the information based on experts about Car1 on the first parameter can be represented in the form of CIFSS as ⟨0.6 ⋅  20.70 , 0.15 ⋅  20.20 ⟩.In this way, all data can be obtained in the form of CIFSS, where both amplitude and phase terms can represent the information on experts's decision which happens periodically.Assume that the expert team had suggested an ideal car (i.e., a car that is in demand) before getting the characteristic information from car maker .The aim of the expert team is to select a suitable car listed by car maker  that is most likely to be the ideal car.Using this information, car dealer  can take the decision to purchase cars from car company  which are in demand in the market to gain maximum profit.

Conclusions
The new introduced concept of complex intuitionistic fuzzy soft sets (CIFSSs) which is a parametric tool has been well proposed and studied in detail along with its important properties and fundamental operations.Based on various well-known distance measures, some new distance measures for CIFSSs have been obtained and extended to find the entropies of complex intuitionistic fuzzy soft sets.A correspondence between the proposed entropies and the distance measures of complex intuitionistic fuzzy soft sets has been well established.An application in the area of multicriteria decision making problem on the basis of the proposed CIFSSs, distance measures, and information measures has also been suggested.