C Library Functions - perturb (3)

NAME

perturb(3f) - [M_orderpack:PERMUTATION] generate a random permutation of an array leaving elements close to initial locations

Synopsis
Description
Options
Examples
Author
Maintainer
License

SYNOPSIS

Subroutine Perturb (INOUTVALS, CLOSENESS)
     ${TYPE} (kind=${KIND}), Intent (InOut) :: INOUTVALS(:)
     Real, Intent (In)                      :: CLOSENESS
Where ${TYPE}(kind=${KIND}) may be

o Real(kind=real32)

o Real(kind=real64)

o Integer(kind=int32)

o Integer(kind=int64)

o Character(kind=selected_char_kind("DEFAULT"),len=*)

DESCRIPTION

Shuffle the array INOUTVALS randomly, leaving elements close to their initial locations.
Nearbyness is controlled by CLOSENESS. The relative proportion of initial order and random order is defined as 1-CLOSENESS / CLOSENESS, thus when CLOSENESS = 0, there is no change in the order whereas the new order is fully random when CLOSENESS = 1.
Note this differs from adding random noise to the values. The original values remain unchanged, their order is just perturbed.
Internally, the routine creates a real array of the indices of INOUTVALS() perturbed by random values that are based on the size of CLOSENESS. The new array is then ranked using RANK(3f) and the resulting index is used to permute the input array.

OPTIONS

INOUTVALS
Array of values to perturb.

CLOSENESS
Proportion of closeness, constrained to the range 0.0(no change) to 1.0(fully random).

EXAMPLES

Sample program:

   program demo_perturb
   ! generate a random perturbation of an array
   use M_orderpack, only : perturb
   implicit none
   character(len=*),parameter :: g=’(*(g0,1x))’
   integer,allocatable :: xout(:,:)
   integer          :: isz, i
   isz=200
      ! randomly perturb location of values
      !
      ! make an array with three initially identical rows of
      ! values perturbed by different amounts
      if(allocated(xout))deallocate(xout)
      allocate(xout(3,isz))
      xout(1,:)=[(i,i=isz,1,-1)]*10
      xout(2,:)=xout(1,:)
      xout(3,:)=xout(1,:)
      ! perturb each row a different amount
      call perturb(xout(1,:),0.0)
      call perturb(xout(2,:),0.1)
      call perturb(xout(3,:),1.0)
      ! show values
      write(*,’(a)’)’count    unchanged  perturbed  random’
      do i=1,size(xout,dim=2)
         write(*,’(*(i8,1x))’)i,xout(:,i)
      enddo
   char: block
   character(len=:),allocatable :: cdont(:)
      cdont=[character(len=20) :: ’a’, ’be’, ’car’, ’dam’,’fan’,’gas’,’egg’]
      isz=size(cdont)
      write(*,g)’Original.................:’,(trim(cdont(i)),i=1,isz)
      call perturb(cdont,1.0)
      write(*,g)’Perturbed ...............:’,(trim(cdont(i)),i=1,isz)
      write(*,g)
   endblock char

   end program demo_perturb

Results:

count unchanged perturbed random 1 2000 1980 80 2 1990 1990 580 3 1980 1890 1690 4 1970 1900 1340 5 1960 1920 1260 6 1950 1950 1220 7 1940 1880 160 8 1930 1960 1620 9 1920 1860 540 10 1910 1930 1300 11 1900 1940 1190 . . . . . . . . . . . . . . . . 189 120 80 1200 190 110 150 800 191 100 120 1430 192 90 170 1410 193 80 140 370 194 70 90 1720 195 60 10 830 196 50 100 1670 197 40 20 470 198 30 70 1020 199 20 60 1540 200 10 30 1810 Original.................: a be car dam fan gas egg Perturbed ...............: a be gas dam fan car egg

AUTHOR

Michel Olagnon, 2000-2012

MAINTAINER

John Urban, 2022.04.16

LICENSE

CC0-1.0

Nemo Release 3.1

perturb (3)

February 23, 2025

Generated by manServer 1.08 from f72e3fd0-13b4-495e-963d-486bef418eff using man macros.

o	Real(kind=real32)
o	Real(kind=real64)
o	Integer(kind=int32)
o	Integer(kind=int64)
o	Character(kind=selected_char_kind("DEFAULT"),len=*)

INOUTVALS
	Array of values to perturb.
CLOSENESS
	Proportion of closeness, constrained to the range 0.0(no change) to 1.0(fully random).