work marginalists previous century extended significantly samuelson approached problems applying individual utility maximization aggregate groups comparative statics compares two different equilibrium states exogenous change variable methods book provided foundation mathematical economics th century ref name samuelson linear models restricted models general equilibrium formulated john von neumann ref name neumann neumann j von ber ein konomisches gleichungssystem und ein verallgemeinerung des brouwerschen fixpunktsatzes ''ergebnisse eines mathematischen kolloquiums'' pp nbsp translated published
Social science Economics Mathematical economics