Algorithms and algorithm analysis of logical difference operation of variable precision upper approximation operator and grade lower approximation operator

The aim of this contribution is to construct new operation of approximation operators, and explore its calculation. It proposes logical difference operation of variable precision upper approximation operator and grade lower approximation operator. Then regular algorithm and structural algorithm are proposed and analyzed, and furthermore it obtains an important conclusion that structural algorithm has advantages in space complexity. Finally the new operation and its algorithms are illustrated by a medical example.