Complex T-spherical fuzzy aggregation operators and their applications in multi-criteria decision making

This thesis consists of six sections. In Section 1, detailed literature review and motivation of the thesis are presented. In Section 2, extensions of the fuzzy sets and complex fuzzy sets are given with their examples. In Section 3, the Dombi operators on CTSFSs are introduced and based on Dombi operators, some aggregation operators, including Complex T-spherical Dombi fuzzy weighted arithmetic averaging (CTSDFWAA) operator, Complex T-spherical Dombi fuzzy weighted geometric averaging (CTSDFWGA) operator, Complex T-spherical Dombi fuzzy ordered weighted arithmetic averaging (CTSDFOWAA) operator, Complex T-spherical Dombi fuzzy ordered weighted geometric averaging (CTSDFOWGA) operator are defined and obtained some of their properties. In Section 4, the multi-criteria decision-making (MCDM) method under the CTSF environment is developed and presented an algorithm for the proposed method. Also, to show the process of the proposed method, an example related to diagnosing the COVID-19 is given. In Section 5, to reveal the advantages and restrictions of the proposed method, a sensitivity analysis is presented. In Section 6, some explanations about the obtained results and works to be presented in the future.