# array

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## array

1. Maths a sequence of numbers or symbols in a specified order
2. Maths a set of numbers or symbols arranged in rows and columns, as in a determinant or matrix
3. Electronics an arrangement of aerials spaced to give desired directional characteristics, used esp in radar
4. Law a panel of jurors
5. Computing a regular data structure in which individual elements may be located by reference to one or more integer index variables, the number of such indices being the number of dimensions in the array
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005

## array

1. A system used in radio astronomy in which a number of discrete elements are connected to form a composite antenna. An element may for example be a single dipole or a dish. The ratio of the aperture area occupied by all the elements to the area that would be occupied by a continuous aperture of the same overall length is called the filling factor; it is a measure of the fraction of the aperture that is actually there. The effective area for an array operating at a wavelength λ with a directivity D is given by
A e = D λ2/4π

It is usually less than the physical area, even when the filling factor is equal to unity, because of small irregularities in the aperture distribution. For a perfect array with a uniform aperture distribution the effective and physical areas are indeed equal.

An array may produce a grating response in one or more directions away from the main lobe (see antenna) which, if the elements of the array were all nondirectional, would be as strong as the main lobe. However, the antenna patterns of the elements together with geometrical effects usually reduce the power in the grating response to an acceptable level. See also aperture synthesis; Butler matrix; feeder.

2. (detector array). An electronic device, such as a CCD, consisting of thousands or millions of individual detectors fabricated on centimeter-sized wafers of silicon or some other material.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006

## array

[ə′rā]
(computer science)
A collection of data items with each identified by a subscript or key and arranged in such a way that a computer can examine the collection and retrieve data from these items associated with a particular subscript or key.
(electronics)
A group of components such as antennas, reflectors, or directors arranged to provide a desired variation of radiation transmission or reception with direction.
(statistics)
The arrangement of a sequence of items in statistics according to their values, such as from largest to smallest.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

## array

A stacked array of yagi antennas
A system of transmitting or receiving aerials made up of two or more identical aerials to give a greatly multiplied gain in desired direction. The aerials may be arranged in the direction of transmission (alignment array or endon array) or perpendicular to it (broadside array).
An array of four yagi antennas, if ideally spaced, will produce approximately 6 dB gain over a single yagi.

## array

(programming)
A collection of identically typed data items distinguished by their indices (or "subscripts"). The number of dimensions an array can have depends on the language but is usually unlimited.

An array is a kind of aggregate data type. A single ordinary variable (a "scalar") could be considered as a zero-dimensional array. A one-dimensional array is also known as a "vector".

A reference to an array element is written something like A[i,j,k] where A is the array name and i, j and k are the indices. The C language is peculiar in that each index is written in separate brackets, e.g. A[i][j][k]. This expresses the fact that, in C, an N-dimensional array is actually a vector, each of whose elements is an N-1 dimensional array.

Elements of an array are usually stored contiguously. Languages differ as to whether the leftmost or rightmost index varies most rapidly, i.e. whether each row is stored contiguously or each column (for a 2D array).

Arrays are appropriate for storing data which must be accessed in an unpredictable order, in contrast to lists which are best when accessed sequentially. Array indices are integers, usually natural numbers, whereas the elements of an associative array are identified by strings.

## array

(architecture)
A processor array, not to be confused with an array processor.

## array

An ordered arrangement of data items. A vector is a one dimensional array; a matrix is a two-dimensional array. Arrays are used in myriad applications from basic database processing to scientific simulation. Most programming languages support arrays by providing indexes into the data. For example, with indexes starting at zero, the hypothetical programming statement Employee[4][9] points to the fifth record (row) and tenth data item (column) of an employee array. See subscript, index and data item.

Array Programming With array indexes starting at 0, in the top array, City would be programmatically identified as Customer[3] (fourth data item). Sales[1][2] would refer to the March figures for Widgets in the bottom array.
Copyright © 1981-2019 by The Computer Language Company Inc. All Rights reserved. THIS DEFINITION IS FOR PERSONAL USE ONLY. All other reproduction is strictly prohibited without permission from the publisher.
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