CO_REDUCE — Reduction of values on the current set of images#
-
CO_REDUCE(A, OPERATOR, RESULT_IMAGE, STAT, ERRMSG)#
CO_REDUCE
determines element-wise the reduction of the value ofA
on all images of the current team. The pure function passed asOPERATION
is used to pairwise reduce the values ofA
by passing either the value ofA
of different images or the result values of such a reduction as argument. IfA
is an array, the deduction is done element wise. IfRESULT_IMAGE
is present, the result values are returned inA
on the specified image only and the value ofA
on the other images become undefined. IfRESULT_IMAGE
is not present, the value is returned on all images. If the execution was successful andSTAT
is present, it is assigned the value zero. If the execution failed,STAT
gets assigned a nonzero value and, if present,ERRMSG
gets assigned a value describing the occurred error.- Parameters
A – is an
INTENT(INOUT)
argument and shall be nonpolymorphic. If it is allocatable, it shall be allocated; if it is a pointer, it shall be associated.A
shall have the same type and type parameters on all images of the team; if it is an array, it shall have the same shape on all images.OPERATION – pure function with two scalar nonallocatable arguments, which shall be nonpolymorphic and have the same type and type parameters as
A
. The function shall return a nonallocatable scalar of the same type and type parameters asA
. The function shall be the same on all images and with regards to the arguments mathematically commutative and associative. Note thatOPERATION
may not be an elemental function, unless it is an intrisic function.RESULT_IMAGE – (optional) a scalar integer expression; if present, it shall have the same value on all images and refer to an image of the current team.
STAT – (optional) a scalar integer variable
ERRMSG – (optional) a scalar character variable
- Standard:
Technical Specification (TS) 18508 or later
- Class:
Collective subroutine
- Syntax:
CALL CO_REDUCE(A, OPERATION, [, RESULT_IMAGE, STAT, ERRMSG])
- Example:
program test integer :: val val = this_image () call co_reduce (val, result_image=1, operation=myprod) if (this_image() == 1) then write(*,*) "Product value", val ! prints num_images() factorial end if contains pure function myprod(a, b) integer, value :: a, b integer :: myprod myprod = a * b end function myprod end program test
- Note:
While the rules permit in principle an intrinsic function, none of the intrinsics in the standard fulfill the criteria of having a specific function, which takes two arguments of the same type and returning that type as result.
- See also:
CO_MIN — Minimal value on the current set of images, CO_MAX — Maximal value on the current set of images, CO_SUM — Sum of values on the current set of images, CO_BROADCAST — Copy a value to all images the current set of images