A linear program can be related to another one reflecting the opposite of itself. These two programs have the same conditions (cost and constraint coefficients), yet they are modeled from counter-viewpoints. Consequently, they reach the same optimal solution mutually. Here, the inversed pair of the original model is called the dual of the original (or primal) model. The dual model interchanges costs and constraints of the primal model, and converts the objective from maximization to minimization.