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### 8.196 `PRODUCT` — Product of array elements

Description:
  Multiplies the elements of ARRAY along dimension DIM if the corresponding element in MASK is `TRUE`.
Standard:
  Fortran 95 and later
Class:
  Transformational function
Syntax:

  `RESULT = PRODUCT(ARRAY[, MASK])`
  `RESULT = PRODUCT(ARRAY, DIM[, MASK])`

Arguments:

  ARRAY | Shall be an array of type `INTEGER`, `REAL` or `COMPLEX`.
  DIM | (Optional) shall be a scalar of type `INTEGER` with a value in the range from 1 to n, where n equals the rank of ARRAY.
  MASK | (Optional) shall be of type `LOGICAL` and either be a scalar or an array of the same shape as ARRAY.

Return value:
  The result is of the same type as ARRAY.

  If DIM is absent, a scalar with the product of all elements in ARRAY is returned. Otherwise, an array of rank n-1, where n equals the rank of ARRAY, and a shape similar to that of ARRAY with dimension DIM dropped is returned.

Example:

                PROGRAM test_product
                  INTEGER :: x(5) = (/ 1, 2, 3, 4 ,5 /)
                  print *, PRODUCT(x)                    ! all elements, product = 120
                  print *, PRODUCT(x, MASK=MOD(x, 2)==1) ! odd elements, product = 15
                END PROGRAM

See also:
  SUM