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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.
An array of four yagi antennas, if ideally spaced, will produce approximately 6 dB gain over a single yagi.
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.
arrayAn 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 points to the fifth record (row) and tenth data item (column) of an employee array. See subscript, index and data item.
|With array indexes starting at 0, in the top array, City would be programmatically identified as Customer (fourth data item). Sales would refer to the March figures for Widgets in the bottom array.|