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Manual Reference Pages  - prime_factors (3)

NAME
prime_factors(3f) - [M_factor] decompose a number into its prime factors

CONTENTS

Synopsis
Description
Options
Example
Pedigree

SYNOPSIS
call prime_factors(number,nprm,iprm,iexp[,verbose]) 

    integer, intent(in)          :: number
    integer, intent(out)         :: nprm
    integer, intent(out)         :: iprm(:)
    integer, intent(out)         :: iexp(:)
    logical, intent(in),optional :: verbose

DESCRIPTION

1. Upon return from PRIME_FACTORS, 

           NUMBER = IPRM(1)**IEXP(1) * IPRM(2)**IEXP(2) * ...
                    *IPRM(NPRM)**IEXP(NPRM)
2. A number represented by a (single-precision) INTEGER value on the VMS VAX cluster can have at most 9 distinct prime factors. On machines where the maximum integer is larger than 2**31 - 1, IPRM and IEXP would, in general, have to be dimensioned larger since larger numbers may have more than 9 distinct prime factors.

OPTIONS

NUMBER
  INTEGER constant or variable, number to be decomposed into prime factors. NUMBER .ge. 2. For 32-bit integers NUMBER <= 2147483647
NPRM INTEGER variable, will contain the number of distinct prime factors of the number.
IPRM INTEGER array of size at least 9, will contain the prime factors of the number.
IEXP INTEGER array of size at least 9, will contain the exponents of the corresponding prime factors.
verbose
  optional LOGICAL constant or variable, controls printing of results.
o false - Results are not printed.
o true - Results are printed.

EXAMPLE

Sample program: 

   program demo_prime_factors
   use M_factor, only : prime_factors
   implicit none
      integer  :: number
      integer  :: iexp(10), iprm(10), nprm
      logical  :: verbose=.true.
      integer  :: ios
      do
        write(*,’(a)’, advance=’no’) ’ Enter number to be factored: ’
        read(*,*,iostat=ios,end=999) number
        if(ios.eq.0)then
           call prime_factors(number, nprm, iprm, iexp, verbose)
        endif
      enddo
   999 continue
   end program demo_prime_factors

PEDIGREE
o Coded at Madison Academic Computing Center, University of Wisconsin, Madison
o FORTRAN 77 Version 1988.09
o Code converted using TO_F90 by Alan Miller, 2000-07-14T11:42:45
o Fortran 2003 version 20160918 by John S. Urban

prime_factors (3) March 11, 2021
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