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C Library Functions  - prank_basic (3)

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NAME

prank_basic(3f) - [M_orderpack:RANK:PARTIAL] partially ranks an array (Quick-Sort)

CONTENTS

Synopsis
Description
Options
Examples
Author
Maintainer
License

SYNOPSIS

Subroutine Prank_Basic (INVALS, IRNGT, NORD)

      ${TYPE} (kind=${KIND}), Intent (In) :: INVALS(:)
      Integer, Intent (Out)               :: IRNGT(:)
      Integer, Intent (In)                :: NORD

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=*)

DESCRIPTION

creates index IRNGT() which partially ranks input array INVALS(), up to order NORD.

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

Internally this routine uses a pivoting strategy such as the one used in finding the median based on the Quick-Sort algorithm. It uses a temporary array, where it stores the partially ranked indices of the values. It iterates until it can bring the number of values lower than the pivot to exactly NORD, and then uses an Insertion-Sort to rank this set, since it is supposedly small.

OPTIONS

INVALS	array to partially rank
IRNGT	array to hold indices of ranked elements
NORD	number of elements to rank

EXAMPLES

Sample program:

   program demo_prank
   ! create index to lowest N values in input array in ascending order
   use,intrinsic :: iso_fortran_env, only : int32, real32, real64
   use M_orderpack, only : prank_basic
   implicit none
   real(kind=real32) :: valsr(2000)
   integer           :: indx(2000)
   integer           :: i
   real,allocatable  :: results(:)
      ! create some random data
      call random_seed()
      call random_number(valsr)
      valsr=valsr*1000000.0-500000.0
      ! get 300 lowest values sorted
      call prank_basic(valsr,indx,300)
      !
      results=valsr(indx(:300))
      ! check if sorted
      do i=1,300-1
         if (results(i+1).lt.results(i))then
            write(*,*)’ERROR: not sorted’
            stop 1
         endif
      enddo
      write(*,*)’random array now sorted’
   end program demo_prank

Results:

    random array now sorted

AUTHOR

Michel Olagnon - Feb. 2000

MAINTAINER

John Urban, 2022.04.16

LICENSE

CC0-1.0

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Nemo Release 3.1

prank_basic (3)

July 22, 2023

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