What is "parameter"

Parameter \Pa*ram"e*ter\, n. [Pref. para- + -meter: cf. F. param[`e]tre.]

1. A constant number which is part of a theory, function, or calculation, whose value is not determined by the form of the theory or equation itself, and may in some cases be arbitrary assigned.

2. Specifically:

   1. (Math.) A term applied to some characteristic magnitude whose value, invariable as long as one and the same function, curve, surface, etc., is considered, serves to distinguish that function, curve, surface, etc., from others of the same kind or family.
      --Brande & C.

   2. (Conic Sections) (in the ellipse and hyperbola), a third proportional to any diameter and its conjugate, or in the parabola, to any abscissa and the corresponding ordinate.

      Note: The parameter of the principal axis of a conic section is called the latus rectum.

3. (Science) Any constant number which is required to calculate values of observed phenomena according to a theory, but the value of which must be determined by experiment, and cannot be calculated from the fundamental assumptions of the theory. In general, a theory which has a large number of parameters, though it may accurately predict experimental results, is considered as having less explanatory power and as being less esthetically pleasing than a theory with fewer parameters.

4. (Crystallog.) The ratio of the three crystallographic axes which determines the position of any plane; also, the fundamental axial ratio for a given species.

5. The limits, guidelines, or assumptions from within which an activity is carried out; as, new arrivals need to learn the parameters of the research in our department.

6. (Computers) A variable used in a calculation within a computer program which must be assigned a value before the calculation can be performed; as, let's plug in the parameters and see what the result is.

7. A characteristic or element, especially one used as a criterion for evaluation or judgment; as, a useful parameter for determining efficiency.

1650s in geometry, from Modern Latin parameter (1630s), from Greek para- "beside, subsidiary" (see para- (1)) + metron "measure" (see meter (n.2)).\n

\nA geometry term until 1920s when it yielded sense of "measurable factor which helps to define a particular system" (1927). Common modern meaning (influenced by perimeter) of "boundary, limit, characteristic factor" is from 1950s. Related: Parametric.

n. 1 (context mathematics physics English) A variable kept constant during an experiment, calculation or similar. 2 (context programming English) An input variable of a procedure definition, that gets an actual value (argument) at execution time ''(formal parameter)''. 3 (context programming English) An actual value given to such a formal parameter ''(argument or actual parameter)''. 4 A characteristic or feature that distinguishes something from others. 5 (context geometry English) In the ellipse and hyperbola, a third proportional to any diameter and its conjugate, or in the parabola, to any abscissa and the corresponding ordinate. 6 (context crystallography English) The ratio of the three crystallographic axis which determines the position of any plane. 7 (context crystallography English) The fundamental axial ratio for a given species.

1. n. a constant in the equation of a curve that can be varied to yield a family of similar curves [syn: parametric quantity]

2. any factor that defines a system and determines (or limits) its performance

3. a quantity (such as the mean or variance) that characterizes a statistical population and that can be estimated by calculations from sample data

A parameter is a quantity which changes characteristics of a system or a function. The term is used in this way in many mathematical sciences.

The term may also have the following meanings:

• Parameter (computer programming)
• Parameters (journal), a journal of the U.S. Army War College
• In linguistics, see Principles and parameters

A parameter (from the Ancient Greek παρά, para: "beside", "subsidiary"; and μέτρον, metron: "measure"), generally, is any characteristic that can help in defining or classifying a particular system (meaning an event, project, object, or situation, etc). That is, a parameter is an element of a system that is useful, or critical, when evaluating the identity of a system; or, when evaluating the performance, status, condition, etc. of a system.

Parameter has more specific, or customized, meanings within the various specialty disciplines, including mathematics, computing and computer programming, engineering, the sciences, statistics, logic, linguistics, etc. And, within and across the various disciplines, careful distinction must be maintained of the different usages of the term parameter and of other terms often associated with it, such as argument, property, axiom, variable, function, attribute, etc.

In computer programming, a parameter is a special kind of variable, used in a subroutine to refer to one of the pieces of data provided as input to the subroutine. These pieces of data are called arguments. An ordered list of parameters is usually included in the definition of a subroutine, so that, each time the subroutine is called, its arguments for that call can be assigned to the corresponding parameters.

Just as in standard mathematical usage, the argument is thus the actual input passed to a function, procedure, or routine, whereas the parameter is the variable inside the implementation of the subroutine. For example, if one defines the add subroutine as def add(x, y): return x + y, then x, y are parameters, while if this is called as add(2, 3), then 2, 3 are the arguments. Note that variables from the calling context can be arguments: if the subroutine is called as a = 2; b = 3; add(a, b) then the variables a, b are the arguments, not only the values 2, 3. See the Parameters and arguments section for more information.

In the most common case, call by value, a parameter acts within the subroutine as a variable initialized to the value of the argument (a local (isolated) copy of the argument if the argument is a variable), but in other cases, e.g. call by reference, the argument supplied by the caller can be affected by actions within the called subroutine (as discussed in evaluation strategy). In call by value, one can thus think of arguments as values (properly, think of the value of arguments as the "arguments" themselves), but in general arguments are not simply values.

The semantics for how parameters can be declared and how the arguments are passed to the parameters of subroutines are defined by the language, but the details of how this is represented in any particular computer system depend on the calling conventions of that system.