SIMSCRIPT II.5 Programming Language

SIMSCRIPT II.5 Programming Language
often be reduced by structuring it so that not all arrays need be reserved concurrently. The release
statement has the general form:
release array-pointer list
Examples are:
release A(*)
release COEFF (*,*), WIDTH (*), DIMENSIONS (J,*)
No access should be attempted to any element of a released array. The array cannot be distinguished
from one that has not been reserved, and an error will result. The array may, of course, be re-reserved
with the same dimensionality.
2.18 Array Pointers as Routine Arguments
Thus far, routine arguments have represented the values of variables, or, in the case of given arguments,
the values of arithmetic expressions. These values are copied between the calling and called
routine, as indicated by the ordering in the argument lists. Such arguments are said to be passed
between routines by value. The value of a subscripted variable may be used in the same way as an
unsubscripted variable. The transmission of an array of values is handled differently. To reserve
and copy entire arrays of values would involve significant inefficiencies. For this reason, when arrays
appear as routine arguments they are passed by reference, that is, a pointer value is passed.
When an array name appears in an argument list, the value of the array base pointer is transmitted,
rather than the array element values. By using this pointer, the receiving routine can access the element
values within the array structure. For an array pointer transmitted as an argument to be recognized
as such, and to enable the correct accessing of its element values, both the mode and
dimensionality of the array represented must be defined to the receiving routine. The following
function routine illustrates the use of an array name as an argument. The function computes the
trace of a square matrix, defined as the sum of the diagonal elements. As the matrix must be square,
it is sufficient to pass one value indicating the number of rows and columns. For example:
function TRACE(MATRIX, SIZE)
define MATRIX as a real, 1-dimensional array
define SIZE as an integer variable
define SUM as a real variable
define I as an integer variable
for I = 1 to SIZE
add MATRIX(I,I) to SUM
return with SUM
end
In this function routine, the argument MATRIX is locally defined as an array. A pointer value is assigned
to it, not by a reserve statement, but by copying the transmitted value of the array base
pointers passed from the calling routine. In this way, the function works with the actual element
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