co_max

Date:: 02-10-2023

NAME

CO_MAX, CO_MIN - Determine maxiumum or minimum value of elements on all images of the current team in a Coarray Fortran application

SYNOPSIS

CO_MAX (SOURCE [, RESULT_IMAGE, STAT, ERRMSG])
CO_MIN (SOURCE [, RESULT_IMAGE, STAT, ERRMSG])

IMPLEMENTATION

Cray Linux Environment (CLE)

DESCRIPTION

CO_MAX and CO_MIN are intrinsic collective subroutines that determine the maximum or minimum value of elements on all images of the current team in a Coarray Fortran application.

For example, if SOURCE is the coarray of values [2, 3, 7] on one image and SOURCE is the coarray of values [4, 1, 8] on all other images of the current team, the values in coarray SOURCE, after executing the statement CALL CO_MAX(SOURCE) are [4, 3, 8].

Support for non-contiguous SOURCE arrays is deferred.

These subroutines accept the following options:

SOURCE: Can be a scalar or an array of type integer, real, or character. If scalar, the computation result is equal to the maximum/minimum value of SOURCE on all images. If SOURCE is an array, the computation result is equal to the maximum/minimum value of all the corresponding elements of SOURCE on the all the images of the current team. It is an INTENT(INOUT) argument.
RESULT_IMAGE: If RESULT_IMAGE is present, the result of the computation is assigned to SOURCE on image RESULT_IMAGE and SOURCE on all other images of the current team becomes undefined. If RESULT_IMAGE is not present, the result is assigned on all images of the current team. Must be an integer in the range 1 … NUM_IMAGES(). It is an INTENT(IN) argument.
STAT: If STAT is present and an error condition occurs, it is assigned a positive value. If it is present and no error condition occurs, it is assigned the value zero. If it is not present and an error condition occurs, error termination is initiated. Must be an integer scalar. It is an INTENT(OUT) argument.
ERRMSG: If ERRMSG is present and an error condition occurs, it is assigned an explanatory message. If it is present an no error condition occurs, it is left unchanged. Must be a character scalar. It is an INTENT(INOUT) argument.

Example

program test
 integer :: image
 integer :: ssrc[*]
 integer :: source(3)[*]
 image=this_image()
 if (image .eq. 2) then
 ssrc[image] = 200
 source(1:3)[image]=(/2,3,7/)
 else
 ssrc[image]=5
 source(1:3)[image]=(/4,1,8/)
 endif
 call co_max(ssrc)
 call co_max(source)
 print *, "image =",image,"  ssrc =", ssrc,"  source =",source
end