variable

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A symbol x is usually defined to be a variable if it may denote any member of a set of objects. A variable is discrete or continuous according to whether its range (the set) is discrete (for example, a subset of the natural numbers) or continuous (for example, all real numbers between two real numbers), respectively. See also Analytic geometry; Number theory; Parametric equation.

In programming, a structure that holds data and is uniquely named by the programmer. It holds the data assigned to it until a new value is assigned or the program is finished.

Control Values

Variables are widely used to hold control values that keep track of something. For example, the C statement FOR (X=0; X<5; X++) performs the instructions following the statement within open and closed curly braces ({ and }) five times, and X is keeping track of that number of iterations. X is a variable set to zero (x=0), incremented by 1 (x++) and compared to 5 (x<5). The reason it is less than 5 (<5) is because we started with 0.

The Equals Sign

Variables are usually assigned with an equal sign. Numbers are unquoted; for example: COUNTER = 1 places the digit 1 in the variable COUNTER. Character data (text) requires quotes; for example: PRODUCT = "abc1234". In some languages, the type of data must be declared before it is assigned; for example, in C/C++, the statement INT COUNTER creates a variable that holds only whole numbers (integers).

Local and Global

A local variable is one that is referenced only within the subprogram, function or procedure it was defined in. A global variable can be used by the entire program. See environment variable, undefined variable and local variable.

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In general: value that changes.

Market research: value that changes as a result of direct intervention (independent variable) or a change in another variable (dependent variable). A variable may be numerical or classificatory, such as gender. In market research, key variables must be identified. For example, an airline might wish to measure its competitive position according to the attitudes of air travelers. The key independent variables that might influence their attitudes (attitude being the dependent variable) would include reservation service, baggage handling, check-in procedures, seat comfort, and so forth. These would have varying values, depending upon consumer opinion of them. In a direct-mail package or advertisement, both the characteristics of the promotion and consumer response to it are variables. To test a promotion, one or more variables such as offer or copy are changed, to measure resultant changes in response. In this example, offer and copy are independent variables, and response is the dependent variable. It is best, when testing, to change only one independent variable per test, so that differences in the dependent variable can clearly be attributed to that change. If more than one independent variable is changed, it will not be clear whether the difference in response is caused by one or more of the changes or, also, whether the change caused by each variable is in the same direction. One change may increase response; the other may decrease it.

adjective

1. Capable of or liable to change: alterable, changeable, fluid, inconstant, mutable, uncertain, unsettled, unstable, unsteady, variant. Archaic various. See change/persist.
2. Following no predictable pattern: capricious, changeable, erratic, fantastic, fantastical, fickle, freakish, inconsistent, inconstant, mercurial, temperamental, ticklish, uncertain, unpredictable, unstable, unsteady, volatile, whimsical. See change/persist, continue/stop/pause.
3. Lacking consistency or regularity in quality or performance: erratic, inconsistent, patchy, spotty, uneven, unsteady. See continue/stop/pause, same/different/compare.

Definition: changing, changeable
Antonyms: invariable, unchangeable, unchanging, unvarying

adj. 1. (of a wind) tending to change direction.

2. (variables) the region of light, variable winds to the north of the northeast trade winds or (in the southern hemisphere) between the southeast trade winds and the westerlies.

See the Introduction, Abbreviations and Pronunciation for further details.

A changing factor which may affect or be affected by another, such as river discharge. Qualitative variables are plotted on a nominal or ordinal scale. Quantitative variables are usually plotted on a ratio or interval scale and the measurements may be continuous or discrete.

(logic) A fundamental notion of modern logic. Intuitively, suppose we have a class of objects about which we might be interested (a domain), and we start with a simple sentence ‘Jane is hungry’. We then strike out mention of Jane, leaving a gap that we mark with the letter x: ‘x is hungry’. This represents something short of a sentence (it is called an open sentence, or predicate). We can ‘point’ the letter x at members of the domain in turn, giving successive sentences like the one with which we started. In such a process the letter x is said to function as a variable taking as values each member of the domain successively. We might conclude the procedure with information like this: somewhere in this process one of the sentences is true, or everywhere such a sentence is true. Such information does not tell us who is hungry, but tells us the quantity of times the predicate is satisfied. The information that somewhere the predicate F applies to the value is represented as (∃x)Fx; the information that it always applies as (∀x)Fx. The expressions (∃…) and (∀…) are the existential and universal quantifiers. The power of the idea only becomes apparent when we consider multiple quantifications. If we start with a relational sentence, ‘Fred loves Jane’ and strike out both names, marking the spaces with different variables, we obtain ‘x loves y’. We can now build very different kinds of information: everyone loves someone: (∀x)(∃y)x loves y; someone loves everyone: (∃x)(∀y)x loves y, and so on. The study of these forms and the relations between them is quantification theory. The basic calculus that formalizes their logic is the predicate calculus.

1. A changeable aspect of a situation that can be manipulated or measured, as in the case of a dependent variable and an independent variable in an experiment.

2. A mathematical symbol that is used to represent some undetermined element from a given set.

A variable is something that is changed or altered in an experiment. For example, to determine the effect of light on plant growth, growing one plant in a sunny window and one in a dark closet will provide evidence as to the effect of light on plant growth.

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1. liable to change; having a range of possible values; liable to deviate from an established type.
2. something that is subject to variation; a quantity or function that can assume any of a set of specified values; a symbol for any unspecified number or quantity.

1. any type of measurement, quantitative or qualitative, of which a series of individual observations is made so that it has, as a principal characteristic, the potential for variability.
2. has the quality of variability.

• v. agent — an agent in the cause of a disease which is capable of variation in intensity, e.g. weather, as contrasted to one that is not variable, e.g. Salmonella dublin.
• concomitant v's — in experimental design these refer to factors that affect the dependent variable, but are not themselves influenced by the treatment (e.g. age of animal). The effect of concomitant variables can be removed by suitable experimental design or by including them in the model.
• continuous v. — one in which all values within a given range are possible, e.g. birth weights of calves.
• v. costs — costs which vary with the dimensions of the activity. Includes seed, fertilizer, teat dip, worm drench. Called also direct costs. See also fixed costs.
• dependent v. — 1. in statistics the variable predicted by a regression equation.
— 2. a variable which depends on other variables for its value.
• discontinuous v. — see discrete variable (below).
• discrete v. — one in which the possible values are not on a continuous scale, e.g. the number of sheep in a flock.
• endogenous v. — dependent variable.
• exogenous v. — independent or predetermined variable.
• independent v. — one not dependent on other variables but capable of affecting dependent variables, thus an input variable.
• spatial v. — a measurement relating to area or location.
• temporal v. — one relating to chronological time.

1. changing; able to vary in quantity or magnitude. n 2. a characteristic that may assume several values.

• Quantities, Relationships, and Operations - variable: unknown placeholder in algebraic expression, opposite of constant, usu. indicated by a letter; (adj) having no fixed value
• General Technology - variable: named program entity capable of representing different values during program execution
• Logic - variable: term with different meanings depending on context
• Reflections and References

Look up variable in Wiktionary, the free dictionary.

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Wikiversity has learning materials about Variable

Variable may refer to:

• Variable (research), a logical set of attributes
• Variable (mathematics), a symbol that represents a quantity in an algebraic expression.
• Variable (computer science), a symbolic name associated with a value and whose associated value may be changed
• Variable star, a type of star (as in astronomical object)
• Dependent and independent variables in statistics

This disambiguation page lists articles associated with the same title. If an internal link led you here, you may wish to change the link to point directly to the intended article.

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Dansk (Danish)
adj. - variabel
n. - variabel, foranderlig, ustadig, omskiftelig

Nederlands (Dutch)
variabele, veranderlijke grootheid/factor (wiskunde), veranderlijke ster, veranderlijke wind, veranderlijk, wispelturig, variabel, afwijkend (biologie)

Français (French)
adj. - (gén, Comput) variable
n. - (gén, Comput, Math) variable

Deutsch (German)
adj. - variabel, veränderbar, unbeständig, wechselhaft
n. - Variable, Veränderliche, veränderliche Größe

Ελληνική (Greek)
adj. - ευμετάβολος, μεταβλητός, ασταθής
n. - (μαθημ.) μεταβλητή

Italiano (Italian)
variabile

Português (Portuguese)
adj. - variável, adaptável
n. - coisa variável, variável (Mat.), estrela variável (Astr.)

Русский (Russian)
изменчивый, непостоянный, переменная величина, переменная звезда, переменный ветер

Español (Spanish)
adj. - variable, cambiadizo, inestable
n. - variable, (mat) cantidad variable

Svenska (Swedish)
adj. - föränderlig, skiftande, ostadig
n. - variabel

中文（简体）(Chinese (Simplified))
可变的, 易变的, 不定的, 变数, 可变物

中文（繁體）(Chinese (Traditional))
adj. - 可變的, 易變的, 不定的
n. - 變數, 可變物

한국어 (Korean)
adj. - 변화하기 쉬운, 변덕스러운, 고르지 못한
n. - 변화하는 것, 변하기 쉬운 성실, 변수

日本語 (Japanese)
adj. - 変わりやすい, 定めない, 変えられる, 変動できる, 可変速式の, 変光する, 変異性の
n. - 変化するもの, 変数

العربيه (Arabic)
‏(صفه) متغير, متقلب (الاسم) متغيرة او كميه متغيرة ( رياضيات)‏

עברית (Hebrew)
adj. - ‮משתנה, ניתן לשינויים, לא-יציב, הפכפך‬
n. - ‮דבר או כמות משתנה, רוח הפכפכת‬

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