Complex interval-valued t-spherical fuzzy sets andtheir applications in multi-criteria decision making

his thesis consists of six chapters. In section 1, literature review, motivation of the thesis and contributions of the thesis in literature are presented. In section 2, the basic definitions and theorems that will be used throughout the thesis are given. In section 3, the concept of complex interval-valued T-spherical fuzzy (CIVT-SF) sets is recalled, and their set- theoretical operations such as union, intersection and complement and score and accuracy functions of CIVT-SF numbers are introduced. Also, arithmetic operations between two CIVT-SF numbers are defined and some results related to these operations are obtained. In section 4, some novel aggregation operators called complex interval-valued T-spherical fuzzy weighted arithmetic aggregation (CIVTSFWAA) operator and complex interval- valued T-spherical fuzzy weighted geometric aggregation (CIVTSFWGA) operator are introduced and some of their basic properties are investigated. In section 5, a decision- making method is developed based on defined averaging operators. Also, to show the progrees of the proposed method an application is given. In section 6, some explanations related to the results of the thesis are presented.