PARALLEL DO

OpenMP* Fortran Compiler Directive: Provides an abbreviated way to specify a parallel region containing a single DO directive.

!$OMP PARALLEL DO [clause[[,] clause] ... ]

do-loop

[!$OMP END PARALLEL DO]

clause

Can be any of the clauses accepted by the DO or PARALLEL directives.

do-loop

Is a DO iteration (a DO loop). It cannot be a DO WHILE or a DO loop without loop control. The DO loop iteration variable must be of type integer.

You cannot branch out of a DO loop associated with a DO directive.

If the END PARALLEL DO directive is not specified, the PARALLEL DO is assumed to end with the DO loop that immediately follows the PARALLEL DO directive. If used, the END PARALLEL DO directive must appear immediately after the end of the DO loop.

The semantics are identical to explicitly specifying a PARALLEL directive immediately followed by a DO directive.

Example

In the following example, the loop iteration variable is private by default and it is not necessary to explicitly declare it. The END PARALLEL DO directive is optional:

  !$OMP PARALLEL DO
        DO I=1,N
            B(I) = (A(I) + A(I-1)) / 2.0
        END DO
  !$OMP END PARALLEL DO

The following example shows how to use the REDUCTION clause in a PARALLEL DO directive:

  !$OMP PARALLEL DO DEFAULT(PRIVATE) REDUCTION(+: A,B)
        DO I=1,N
          CALL WORK(ALOCAL,BLOCAL)
          A = A + ALOCAL
          B = B + BLOCAL
        END DO
  !$OMP END PARALLEL DO

PARALLEL DO

Example

See Also