“…In extension theory, a correlation function is used to indicate the extent to which an element has a certain property. In the following, according to the definition of extension theory, a formula for calculating the correlation degree [30,31,32,33] of each evaluation index is given. kjfalse(xifalse)={ρfalse(xi,b,X0false)ρfalse(xi,b,Xfalse)−ρfalse(xi,b,X0false)xi∉X0ρfalse(xi,b,x0false)ρfalse(xi,b,Xfalse)−ρfalse(xi,b,X0false)+amji−bmjixi∈X0ρfalse(xj,b,X0false)amji−bmjiρfalse(xi,b,X0false)=ρfalse(x…”