Specifies that an array is an allocatable array with a deferred
  shape.  The shape of an allocatable array is determined when an
  ALLOCATE statement is executed, dynamically allocating space for
  the array.

  The ALLOCATABLE attribute can be specified in a type declaration
  statement or an ALLOCATABLE statement, and takes one of the
  following forms:

  Type Declaration Statement:

   type, [att-ls,] ALLOCATABLE [,att-ls] :: a[(d-spec)] [,a[(d-spec)]]...

  Statement:

   ALLOCATABLE [::] a[(d-spec)] [,a[(d-spec)]]...

     type        Is a data type specifier.

     att-ls      Is an optional list of attribute specifiers.

     a           Is the name of the allocatable array; it must
                 not be a dummy argument or function result.

     d-spec      Is a deferred-shape specification (: [,:]...).
                 Each colon represents a dimension of the array.

  If the array is given the DIMENSION attribute elsewhere in the
  program, it must be declared as a deferred-shape array.

  When the allocatable array is no longer needed, it can be
  deallocated by execution of a DEALLOCATE statement.

  During program execution, the allocation status of an allocatable
  array is one of the following:

   o  Not currently allocated

      The array was never allocated or the last operation performed
      on it was a deallocation.  Deallocation is performed:

       -  Explicitly, by using a DEALLOCATE statement.

       -  By default, when the allocatable array is a local variable
          of a procedure that does not have the SAVE attribute and is
          terminated by an END or RETURN statement.

      An array that is not currently allocated must not be referenced
      or defined.

   o  Currently allocated

      The array was allocated by an ALLOCATE statement.  Such an
      array can be referenced, defined, or deallocated.

  An allocatable array cannot be specified in a COMMON, EQUIVALENCE,
  DATA, or NAMELIST statement.

  Allocatable arrays are not saved by default.  If you want to retain
  the values of an allocatable array across procedure calls, you must
  specify the SAVE attribute for the array.

  The ALLOCATABLE attribute is compatible with the AUTOMATIC,
  DIMENSION (with deferred shape), PRIVATE, PUBLIC, SAVE, STATIC,
  TARGET, and VOLATILE attributes.

  EXAMPLES:

  The following example shows a type declaration statement specifying
  the ALLOCATABLE attribute:

     REAL, ALLOCATABLE :: Z(:, :, :)

  The following is an example of the ALLOCATABLE statement:

     REAL A, B(:)
     ALLOCATABLE :: A(:,:), B