Dimensioned Arrays

Each value in a dimensioned array is called an element of the array. Dimensioned arrays can be one- or two-dimensional.

A one-dimensional array is called a vector. Its elements are arranged sequentially in memory. An element of a vector is specified by the variable name followed by the index of the element enclosed in parentheses. The index of the first element is 1. The index can be a constant or an expression. Two examples of valid vector element specifiers are:

A(1)
COST(35)

A two-dimensional array is called a matrix. The elements of the first row are arranged sequentially in memory, followed by the elements of the second row, and so on. An element of a matrix is specified by the variable name followed by two indices enclosed in parentheses. The indices represent the row and column position of the element. The indices of the first element are (1,1). Indices can be constants or expressions. The indices used to specify the elements of a matrix that has four columns and three rows are illustrated by the following:

1,1     1,2     1,3     1,4
2,1     2,2     2,3     2,4
3,1     3,2     3,3     3,4

Two examples of valid matrix element specifiers are:

OBJ(3,1)
WIDGET(7,17)

Vectors are treated as matrices with a second dimension of 1. COST(35) and COST(35,1) are equivalent specifications and can be used interchangeably.

Both vectors and matrices have a special zero element that is used in MATPARSE statement, MATREAD statements, and MATWRITE statements. The zero element of a vector is specified by vector.name(0), and the zero element of a matrix is specified by matrix.name(0,0). Zero elements are used to store fields that do not fit in the dimensioned elements on MATREAD or MATPARSE statements.

Dimensioned arrays are allocated either at compile time or at run time, depending on the flavor of the account. Arrays allocated at run time are called standard arrays. Arrays allocated at compile time are called fixed arrays. Standard arrays are redimensionable; fixed arrays are not redimensionable and do not have a zero element. All arrays are standard unless the program is compiled in a PICK, IN2, or REALITY flavor account, in which case they are fixed arrays. To use fixed arrays in PIOPEN, INFORMATION and IDEAL flavor accounts, use the STATIC.DIM option of the $OPTIONS statement. To use standard arrays in PICK, IN2, and REALITY flavor accounts, use $OPTIONS -STATIC.DIM.