Input and Output represent the (unidirectional) connections of a dynamic system resp. of its elements with its environment. Usually there is more than one input and output of a system. While inputs represent influences from the environment to the system, outputs represent the effects of the system on its environment. If there is no connection between the system and its environment, the system is called closed.
The relation between input and output of a system is of particular interest. By the assumption of the black box hypothesis (ignoring the inner structure and relations of the system) one can try to analyze the output of the system in its response to a change in the input. If a deterministic system always responds to all certain inputs in the same way the system is called passive, if not, it is called active. If the relations between input and output are stochastic in nature, one can study the conditional probability distributions of the output to get more information on the system..
Input-Output Analysis, developed by Nobel Laureate Wassily Leontief (1905-1999), is a method to study economic systems on a local, regional, (mainly) national or global basis. With the help of an Input-Output Table (listing the value of intermediary goods and the value added for each firm or industry) one can predict the effects of final demand (consumption, investment, foreign trade) on total output. Economical input-output analysis goes back to Francois Quesnay (1694-1774) who as surgeon in ordinary to king Louis XV of France was inspired by blood circulation and developed the first tables of an economy. Leontief did not start from scratch. He expanded Marx' reproduction schemes and the planning tools of the former Soviet Union up to a point where Input-Output Analysis became applicable empirically.
Fleissner, Peter (28/02/09)
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