Two categories of CP formulation: 1. Nonlinear complementarity problem: uses an exact model of the friction cone. 2. Linear complementarity problem: uses a polyhedral approximation of the friction cone. This is a simpler problem to solve. # LCP features ## Solver - pivoting methods (e.g., Lemke’s or Dantzig’s algorithm) # NCP ## Solver - iterative methods (e.g., projected successive over-relaxation, projected Gauss–Seidel methods)