PRODUCT

Intel® Fortran Compiler Classic and Intel® Fortran Compiler Developer Guide and Reference

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Date 9/08/2022

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PRODUCT

Transformational Intrinsic Function (Generic): Returns the product of all the elements in an entire array or in a specified dimension of an array.

result = PRODUCT (array [, mask])

result = PRODUCT (array, dim [, mask])

array	(Input) Must be an array of type integer, real, or complex.
dim	(Input) Must be a scalar integer with a value in the range 1 to n, where `n` is the rank of array.
mask	(Input; optional) Must be of type logical and conformable with array.

Results

The result is an array or a scalar of the same data type as array.

The result is a scalar if dim is not specified or array has rank one.

The following rules apply if dim is not specified:

If PRODUCT(array) is specified, the result is the product of all elements of array. If array has size zero, the result is 1.
If PRODUCT(array, MASK= mask) is specified, the result is the product of all elements of array corresponding to true elements of mask. If array has size zero, or every element of mask has the value .FALSE., the result is 1.

The following rules apply if dim is specified:

If array has rank one, the value is the same as PRODUCT(array[,MASK= mask]).
An array result has a rank that is one less than array, and shape (d₁, d₂, ..., d_dim-1, d_dim+1, ..., d_n), where (d₁, d₂, ..., d_n) is the shape of array.
The value of element (s₁, s₂, ..., s_dim-1, s_dim+1, ..., s_n) of PRODUCT(array, dim[, mask]) is equal to PRODUCT(array(s₁, s₂, ..., s_dim-1, :, s_dim+1, ..., s_n) [,MASK= mask(s₁, s₂, ..., s_dim-1, :, s_dim+1, ..., s_n)]).

Example

PRODUCT ((/2, 3, 4/)) returns the value 24 (the product of 2 * 3 * 4). PRODUCT ((/2, 3, 4/), DIM=1) returns the same result.

PRODUCT (C, MASK=C .LT. 0.0) returns the product of the negative elements of C.

A is the array

  [ 1  4  7 ]
  [ 2  3  5 ].

PRODUCT (A, DIM=1) returns the value (2, 12, 35), which is the product of all elements in each column. 2 is the product of 1 * 2 in column 1. 12 is the product of 4 * 3 in column 2, and so forth.

PRODUCT (A, DIM=2) returns the value (28, 30), which is the product of all elements in each row. 28 is the product of 1 * 4 * 7 in row 1. 30 is the product of 2 * 3 * 5 in row 2.

If array has shape (2, 2, 2), mask is omitted, and dim is 1, the result is an array result with shape (2, 2) whose elements have the following values.

Resultant array element	Value
result(1, 1)	`array`(1, 1, 1) * `array`(2, 1, 1)
result(2, 1)	`array`(1, 2, 1) * `array`(2, 2, 1)
result(1, 2)	`array`(1, 1, 2) * `array`(2, 1, 2)
result(2, 2)	`array`(1, 2, 2) * `array`(2, 2, 2)

The following shows another example:

 INTEGER array (2, 3)
 INTEGER AR1(3), AR2(2)
 array = RESHAPE((/1, 4, 2, 5, 3, 6/),(/2,3/))
 ! array is  1 2 3
 !           4 5 6
 AR1 = PRODUCT(array, DIM = 1) ! returns [ 4 10 18 ]
 AR2 = PRODUCT(array, MASK = array .LT. 6, DIM = 2)
                                  ! returns [ 6 20 ]
 END

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PRODUCT

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