C Library Functions - prank_decreasing (3)

NAME

prank_decreasing(3f) - [M_orderpack:RANK:PARTIAL] partially ranks an array in DECREASING order.

Synopsis
Description
Options
Examples
Author
Maintainer
License

SYNOPSIS

Subroutine Prank_Decreasing (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)

DESCRIPTION

Same as PRANK(3f), but in decreasing order.
PRANK_DECREASING(3f) partially ranks input array INVALS() in decreasing order up to order NORD, placing the indices pointing to the selected values into IRNGT().
Internally this routine uses a pivoting strategy such as the one of finding the median based on the quick-sort algorithm, but we skew the pivot choice to try to bring it to NORD as fast as possible. It uses two temporary arrays, where it stores the indices of the values larger than the pivot (IHIGT), and the indices of values smaller than the pivot that we might still need later on (ILOWT). It iterates until it can bring the number of values in IHIGT to exactly NORD, and then uses an insertion sort to rank this set, since it is supposedly small.

OPTIONS

INVALS Array to rank

IRNGT returned rank array, indicating order of values in INVALS from largest to smallest

NORD number of values to return in IRNGT

EXAMPLES

Sample program:

   program demo_prank_decreasing
   ! create index to lowest N values in input array in decreasing order
   use M_orderpack, only : prank_decreasing
   implicit none
   character(len=*),parameter :: g=’(*(g0,1x))’
   integer,allocatable :: INVALS(:)
   integer,allocatable :: irngt(:)
   integer :: nord
   INVALS=[10,5,7,1,4,5,6,8,9,10,1]
   nord=5
   allocate(irngt(nord))
      write(*,g)’ORIGINAL:’,INVALS
      call prank_decreasing(INVALS,irngt,nord)
      write(*,g)’NUMBER OF INDICES TO RETURN:’,nord
      write(*,g)’RETURNED INDICES:’,irngt
      write(*,g)nord,’MAXIMUM VALUES:’,INVALS(irngt(:nord))
   end program demo_prank_decreasing

Results:

ORIGINAL: 10 5 7 1 4 5 6 8 9 10 1 NUMBER OF INDICES TO RETURN: 5 RETURNED INDICES: 1 10 9 8 7 5 MAXIMUM VALUES: 10 10 9 8 6

AUTHOR

Michel Olagnon - Feb. 2011

MAINTAINER

John Urban, 2022.04.16

LICENSE

CC0-1.0

Nemo Release 3.1

prank_decreasing (3)

July 22, 2023

Generated by manServer 1.08 from e6f549df-3b9f-4430-aaeb-8b436d7258ad using man macros.

INVALS	Array to rank
IRNGT	returned rank array, indicating order of values in INVALS from largest to smallest
NORD	number of values to return in IRNGT