215 lines
7.6 KiB
Fortran
215 lines
7.6 KiB
Fortran
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!=======================================================================
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MODULE FACTORIALS
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!
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! This module provides factorials and other related numbers
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!
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!
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USE ACCURACY_REAL
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USE REAL_NUMBERS, ONLY : ZERO,ONE
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!
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CONTAINS
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!=======================================================================
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!
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FUNCTION FAC(N)
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!
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! This function computes the factorial of n
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!
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! Input parameters:
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!
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! * N : integer
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!
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! Output variables :
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!
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! * FAC : n!
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!
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!
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! Author : D. Sébilleau
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!
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! Last modified : 5 Aug 2020
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IMPLICIT NONE
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!
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REAL (WP) :: FAC
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REAL (WP) :: FACT(50)
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!
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REAL (WP) :: FLOAT
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!
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INTEGER :: N,K
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INTEGER :: LOGF
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!
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LOGF = 6 !
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!
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IF(N > 50) THEN !
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WRITE(LOGF,10) !
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STOP !
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END IF !
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!
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FACT(1) = ONE !
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!
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DO K = 2, N !
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FACT(K) =FACT(K-1) * FLOAT(K) !
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END DO !
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!
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FAC = FACT(N) !
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!
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10 FORMAT(5X,'<<<<< DIMENSION ERROR IN FAC FUNCTION >>>>>',/, &!
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5X,'<<<<< N SHOULD BE <= 50 OR REDIMENSION >>>>>',//) !
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!
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END FUNCTION FAC
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!
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!=======================================================================
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!
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SUBROUTINE COMBINATORIAL(NMAX,NUMBER,CN)
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!
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! This subroutine computes numbers resulting from combinatorics
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!
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! --> This version if for integers only <--
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!
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!
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!
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! Input variables :
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!
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! NMAX : upper value of n
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! NUMBER : type of numbers computed
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! ---> 'BINOMIAL ' : binomial coefficients
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! ---> 'POCHHAMMER' : Pochhammer coefficients
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! ---> 'STIRLING1S' : signed Stirling numbers of 1st kind
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! ---> 'STIRLING1U' : unsigned Stirling numbers of 1st kind
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! ---> 'STIRLING2N' : Stirling numbers of 2nd kind
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!
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! Output variables :
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!
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!
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! CN : resulting numbers
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!
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!
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! Author : D. Sébilleau
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!
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! Last modified : 31 Jan 2019
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!
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IMPLICIT NONE
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!
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REAL (WP) :: LG(NMAX),CN(0:NMAX,0:NMAX),X
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!
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REAL (WP) :: EXP,FLOAT
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!
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INTEGER :: NMAX,I,J,K,N
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!
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CHARACTER (LEN = 10) :: NUMBER
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!
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! Initialization of the array
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!
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DO I = 0,NMAX !
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DO J = 0,NMAX !
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CN(I,J) = ZERO !
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END DO !
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END DO !
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!
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IF(NUMBER == 'BINOMIAL ') THEN ! ( N )
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! ! ( K )
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CALL LOG_GAMMA(NMAX,LG) !
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!
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CN(0,0) = ONE !
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DO N = 1,NMAX !
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DO K = 1,NMAX-N !
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X = LG(N)-LG(K)-LG(N-K) !
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CN(N,K) = EXP(X) !
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END DO !
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END DO !
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!
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ELSE IF(NUMBER == 'POCHHAMMER') THEN ! (N)_K
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!
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CALL LOG_GAMMA(NMAX,LG) !
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!
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CN(0,0) = ONE !
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DO N = 1,NMAX !
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DO K = 1,NMAX-N !
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X = LG(N+K)-LG(N) !
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CN(N,K) = EXP(X) !
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END DO !
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END DO !
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!
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ELSE IF(NUMBER == 'STIRLING1U') THEN ! c(N,K)
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!
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CN(0,0) = ONE !
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CN(NMAX,0) = ZERO !
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!
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DO N = 1, NMAX-1 !
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CN(N,0) = ZERO !
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DO K = 1, NMAX-N+1 !
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CN(N+1,K) = FLOAT(N) * CN(N,K) + CN(N,K-1) !
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END DO !
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END DO !
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!
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ELSE IF(NUMBER == 'STIRLING1S') THEN ! s(N,K)
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!
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CN(0,0) = ONE !
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CN(NMAX,0) = ZERO !
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!
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DO N = 1, NMAX-1 !
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CN(N,0) = ZERO !
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DO K = 1, NMAX-N+1 !
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CN(N+1,K) = - FLOAT(N) * CN(N,K) + CN(N,K-1) !
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END DO !
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END DO !
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!
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ELSE IF(NUMBER == 'STIRLING2N') THEN ! S(N,K)
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!
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CN(0,0) = ONE !
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CN(NMAX,0) = ZERO !
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!
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DO N = 1, NMAX-1 !
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CN(N,0) = ZERO !
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DO K = 1,NMAX-N+1 !
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CN(N+1,K) = FLOAT(K) * CN(N,K) + CN(N,K-1) !
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END DO !
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END DO !
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!
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END IF
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!
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END SUBROUTINE COMBINATORIAL
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!
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!=======================================================================
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!
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SUBROUTINE LOG_GAMMA(NMAX,LG)
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!
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! This subroutine computes the logarithm of the Gamma function for
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! integer values (i.e. Log(n!))
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!
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!
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! Input variables :
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!
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! NMAX : upper value of n
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!
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! Output variables :
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!
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! LG : array containing Log(n!)
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!
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! Author : D. Sébilleau
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!
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! Last modified : 5 Aug 2020
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!
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!
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IMPLICIT NONE
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!
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REAL (WP) :: LG(NMAX)
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!
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REAL (WP) :: LOG,FLOAT
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!
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INTEGER :: NMAX,I,J
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!
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LG(1) = ZERO !
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!
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DO I = 2,NMAX !
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J = I - 1 !
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LG(I) = LG(J) + LOG(FLOAT(J)) !
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END DO !
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!
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END SUBROUTINE LOG_GAMMA
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!
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END MODULE FACTORIALS
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