pack(3I)

NAME
     PACK - Packs an array into an array of rank one under control of a
     mask

SYNOPSIS
     PACK ([ARRAY=]array, [MASK=]mask [,[VECTOR=]vector])

STANDARDS
     Fortran

DESCRIPTION
     The PACK intrinsic function packs an array into an array of rank one
     under control of a mask.  It can be used for array construction.  It
     accepts the following arguments:

     array     Can be of any type.  It must not be scalar.

     mask      Must be of type logical and must be conformable with array.

     vector    Must be of the same type as array and must have rank one.
               vector must have at least as many elements as there are true
               elements in mask.  If mask is scalar with the value true,
               vector must have at least as many elements as there are in
               array.

     PACK is a transformational function.  The name of this intrinsic
     cannot be passed as an argument.

RETURN VALUES
     The result is an array of rank one of the same type as array.  If
     vector is present, the result size is that of vector; otherwise, the
     result size is the number t of true elements in mask unless mask is
     scalar with the value true in which case the result size is the size
     of array.

     Element i of the result is the element of array that corresponds to
     the ith true element of mask, taking elements in array element order,
     for i=1, 2, ..., t.  If vector is present and has size n>t, element i
     of the result has the value vector(i), for i=t+1, ..., n.

EXAMPLES
     Example 1:  Assume that N = (/1,-1,3/).  The following are true:

     * PACK(N,MASK=N.LT.0) yields (/-1/).

     * PACK(N,MASK=.TRUE.) yields (/1,-1,3/).

     Example 2:  Assume array M is as follows:

     | 0 0 0 |
     | 9 0 0 |
     | 0 0 7 |

     The nonzero elements of array M can be gathered by the PACK function.
     The following are the results:

     * PACK(M,MASK=M.NE.0) yields (/9,7/).

     * PACK(M,MASK=M.NE.0,VECTOR=(/2,4,6,8,10,12/)) yields
       (/9,7,6,8,10,12/).