refsor Interface

sort(3f) - [M_orderpack:SORT] Sorts array into ascending order
             (Quick-sort)

 Subroutine Sort (INOUTVALS)

   ${TYPE} (kind=${KIND}), Intent (InOut) :: INOUTVALS(:)

Where ${TYPE}(kind=${KIND}) may be

   o Real(kind=real32)
   o Real(kind=real64)
   o Integer(kind=int32)
   o Character(kind=selected_char_kind("DEFAULT"),len=*)

Sorts INOUTVALS into ascending order (Quick-sort)

This version is not optimized for performance, and is thus not as
difficult to read as some other ones.

Internally, This subroutine uses Quick-sort in a recursive
implementation, and insertion sort for the last steps with small
subsets. It does not use any work array.

The Quick-sort
chooses a "pivot" in the set, and explores the array from
both ends, looking for a value > pivot with the increasing index,
for a value <= pivot with the decreasing index, and swapping them
when it has found one of each. The array is then subdivided in
two subsets:

    { values <= pivot} {pivot} {values > pivot}

It then recursively calls the procedure to sort each subset. When
the size of the subarray is small enough, it switches to an insertion
sort that is faster for very small sets.

 INOUTVALS      array to sort

program demo_sort
! sort array in ascending order
use,intrinsic :: iso_fortran_env, only : int32, real32, real64
use M_orderpack, only : sort
implicit none
! an insertion sort is very efficient for very small arrays
! but generally slower than methods like quick-sort and merge-sort.
real(kind=real64) :: valsd(2000)
integer           :: i
   call random_seed()
   call random_number(valsd)
   valsd=valsd*1000000.0-500000.0
   call sort(valsd)
   do i=1,size(valsd)-1
      if (valsd(i+1).lt.valsd(i))then
         write(*,*)'not sorted'
         stop 3
      endif
   enddo
   write(*,*)'random arrays are now sorted'
end program demo_sort

 random arrays are now sorted

Michel Olagnon - Apr. 2000

John Urban, 2022.04.16

CC0-1.0