C MARCH 3, 2001; MARCH 24, 2005
C FUNCTION DECLARATIONS FOR THE COST FUNCTION OF A GENERALIZED
C NETWORK FLOW PROBLEM.  THE FUNCTIONS C(I,F), DC(I,F), DCINV(I,F)
C GIVE THE FUNCTION VALUE, DERIVATIVE VALUE, DERIVATIVE INVERSE VALUE
C FOR A LINEAR COST FUNCTION OR AN
C          ENTROPY COST FUNCTION   F*LOG(F/CDAT(I,1)) - F
C FOR ARC I WITH FLOW F.
C THE FUNCTION PARAMETERS A(I), CDAT(I,1) ARE SPECIFIED IN THE
C ASCII FILE   NL013.DAT
C A(I) IS THE LINEAR COST COEFFICIENT.  CDAT(I,1) IS THE ENTROPY
C COST COEFFICIENT.  CDAT(I,1)=0.0 INDICATES A LINEAR COST ARC.

      FUNCTION C(I,F)
      IMPLICIT NONE
      INTEGER*4 MAXARCS,MAXNDAT,I,N,NA
      PARAMETER (MAXARCS=20000, MAXNDAT=5)
      REAL*8 A(MAXARCS),CDAT(MAXARCS,MAXNDAT),F,C,LARGE,ZERO
      COMMON /SCALARS/N,NA,LARGE,ZERO
      COMMON /LCOS/A
      COMMON /QCO1/CDAT

      IF (CDAT(I,1).EQ.ZERO) THEN
        C=A(I)*F
      ELSE
        IF (F.LE.0.0) THEN
          C=-F
        ELSE
          C=F*DLOG(F/CDAT(I,1))-F
        END IF
      END IF
      RETURN
      END
      
      FUNCTION DC(I,F)
      IMPLICIT NONE
      INTEGER*4 MAXARCS,MAXNDAT,I,N,NA
      PARAMETER (MAXARCS=20000, MAXNDAT=5)
      REAL*8 A(MAXARCS),CDAT(MAXARCS,MAXNDAT),F,DC,LARGE,ZERO
      COMMON /SCALARS/N,NA,LARGE,ZERO
      COMMON /LCOS/A
      COMMON /QCO1/CDAT
  
      IF (CDAT(I,1).EQ.ZERO) THEN
        DC=A(I)
      ELSE
        IF (F.LE.0.0) THEN
          DC=-LARGE
        ELSE
          DC=DLOG(F/CDAT(I,1))
        END IF
      END IF
      RETURN
      END
      
      FUNCTION DCINV(I,T)
      IMPLICIT NONE
      INTEGER*4 MAXARCS,MAXNDAT,I,N,NA
      PARAMETER (MAXARCS=20000, MAXNDAT=5)
      REAL*8 A(MAXARCS),CDAT(MAXARCS,MAXNDAT),T,DCINV,LARGE,ZERO
      COMMON /SCALARS/N,NA,LARGE,ZERO
      COMMON /LCOS/A
      COMMON /QCO1/CDAT
      
      if (t.gt.50) print*,'tension large and positive',i,t
      if (t.lt.-50) print*,'tension large and negative',i,t
      
      DCINV=CDAT(I,1)*DEXP(T)
      IF (DCINV.GT.LARGE) THEN
        DCINV=LARGE
      ELSE
        IF (DCINV.LT.1.0/LARGE) DCINV=1.0/LARGE
      END IF
      
      RETURN
      END