“…In 1966, Hartman and Stampacchia [24] first introduced the variational inequality problem (VIP) for used in the study of partial differential equations with unilateral boundary conditions and free boundary value problems of elliptic type from mechanics. The VIP has been intensively and wildly studied and it has been found that it also can be applied to real world problems such as equilibrium problems, optimal control problems, machine learning, signal processing and linear inverse problems (see, for example, [15,16,29,30,34,37,50]).…”