Logical AND model of variable precision upper approximation operator and grade lower approximation operator

The paper is to combine precision and grade, and explore new extended rough set model. Based on logical AND requirement of precision and grade, this paper proposes logical AND model of variable precision upper approximation operator and grade lower approximation operator. In the new model, basic structure and properties are obtained, and furthermore regular algorithm and structural algorithm are proposed. The new model has extended classical rough set model partially, and a medical example is given to illustrate it.