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'Input' is the term denoting either an entrance or changes which are inserted into a system and which activate/modify a process. It is an abstract concept, used in the modeling, system(s) design and system(s) exploitation. It is usually connected with other terms, ''e.g.'', input field, input variable, input parameter, input value, input signal, input device and input file.
From the most general systemics perspective, input is a subjective concept and depends on how the system is used. In such sense, the same system can have different inputs in different applications.
In the case of a process description/model, the concept input is closely connected with the concept output. Here, what enters is called input and what exits is called output.
Example:
For an abstract system ''A(x,y,p)'', where ''x,y'' are variables and ''p'' is a parameter, ''x'' may denote input (variable) and ''y'' may denote the output for a process: ''y = f(p,x)'', but, for another goal/(system application), the system ''A'' can be the carrier of a process ''x = g(p,y)'', where ''y'' is an input and ''x'' is an output.
Usually, in the modeling of a problem/process, input are these variables which are known and output are those unknown to us yet.
In recognition that the quality of the input can be crucial to the value of the output, a famous saying teaches us "Garbage IN, Garbage OUT" (GIGO). http://www.google.com/search?hl=en&q=define%3A+GIGO&btnG=Google+Search
In different contexts, 'input' has several more concrete domain-dependent meanings.

Contents

Information processing

Control theory

Equity theory

Economic theory

See also

Information processing

In information processing, 'input' refers to either information received or the process of receiving it;

★ In human-computer interaction, input is the information produced by the user with the purpose of controlling the computer program. The 'user interface' determines what kinds of input the program accepts (for example, control strings or text typed with keyboard and mouse clicks).

★ Input also comes from networks and storage devices such as disk drives.

Control theory

In control theory, the 'inputs' of a system are the signals that can be observed or affected that feed into the system. Specifically, inputs are differentiated from states.

Equity theory

In equity theory, 'inputs' are the skills, time, effort, expertise, experience or qualifications that an employee brings to his job.

Economic theory

In economics, inputs refer to priced or unpriced resources used in a production process, and outputs refer to the priced or unpriced results of that process. Normally, inputs are regarded as costs, and outputs as products. Outputs may be valued gross (before deduction of costs from sales) or net (after deduction of costs from sales). Input-output economics was popularised by the economist Wassily Leontief who devised an ingenious system of input and output accounts and matrices to analyse the flows of goods and services between different sectors of a national economy. In national accounts an attempt is made to value national inputs and outputs according to consistent valuation principles, to measure the creation and distribution of wealth.

See also

★ Output

★ Input/output

★ Gross Output

★ Net output