Complementarity problems were originally studied because the Karush–Kuhn–Tucker conditions in linear programming and quadratic programming constitute a linear complementarity problem (LCP) or a mixed complementarity problem (MCP). In 1963 Lemke and Howson showed that, for two person games, computing a Nash equilibrium point is equivalent to an LCP. In 1968 Cottle and Dantzig unified linear and quadratic programming and bimatrix games. Since then the study of complementarity problems and variational inequalities has expanded enormously.
Areas of mathematics and science that contributed to the development of complementarity theory include: optimization, equilibrium problems, variational inequality theory, fixed point theory, topological degree theory and nonlinear analysis.
Billups, Stephen; Murty, Katta (2000). "Complementarity Problems". Journal of Computational and Applied Mathematics. 124 (1–2): 303–318. Bibcode:2000JCoAM.124..303B. doi:10.1016/S0377-0427(00)00432-5. http://www-personal.umich.edu/~murty/LCPart.ps ↩