SUBROUTINE BINDERIV(ID,IG,V2DERIV)
C Calculate derivatives of squared visibilities of binaries for BINFIT.
C The quantities calculated, V2DERIV, are the derivatives of the squared 
C visibility of the ID,IG-th data point, where ID labels the scan and IG 
C labels the filter, with respect to all parameter types (J=1 to 8) of
C all filters IFF and all components ICC.
C     J.T. Armstrong          1 Feb 1991

      INCLUDE 'BINFIT.INC'

      COMPLEX*16 DERIV(MXMOD,MXFILT,8), SUMDERIV(MXMOD,MXFILT,8),CONJ
      REAL*8     V2DERIV(MXMOD,MXFILT,8) 
      INTEGER*4  ICC, IGG

      EXTERNAL CONJ

C     WRITE(OUTC,'(A,I2,1X,I2)') ' Entering BINDERIV w/ ID,IG = ',ID,IG
C Zero the SUMDERIV array
D     WRITE(OUTC,*) ' NCOMP, NFILT = ',NCOMP,NFILT
      DO ICC = 1, NCOMP
          DO IGG = 1, NFILT
              DO J = 1, 8
D                 WRITE(OUTC,'(A,I3,A,I3,A,I3,A)')
D    1                ' Zeroing SUMDERIV(',ICC,',',IGG,',',J,').'
                  SUMDERIV(ICC,IGG,J) = CMPLX(0., 0.)
                  V2DERIV(ICC,IGG,J) = 0.
              END DO
          END DO
      END DO

C Sum over contributions to derivatives the components.  BWDERIV returns
C complex derivatives of the complex visibility (NOT of the visibility 
C squared) with respect to parameters of all components, filters, and 
C parameter types.
      DO IC = 1, NCOMP
C         WRITE(OUTC,'(A,3(I2,1X))')
C    1               ' Going to BWDERIV w/ IC,ID,IG = ',IC,ID,IG
          CALL BWDERIV(IC,ID,IG,DERIV)
D         WRITE(OUTC,*) ' Returned from BWDERIV'
          DO ICC = 1, NCOMP
              DO IGG = 1, NFILT
                  DO J = 1, 8
                      IF(VARY(ICC,IGG,J)) THEN
                          SUMDERIV(ICC,IGG,J) 
     1                          = SUMDERIV(ICC,IGG,J) + DERIV(ICC,IGG,J)
C                        WRITE(OUTC,'(A,I2,A,I2,A,I2,A,G11.4,1X,G11.4)') 
C    1                        ' SUMDERIV(',ICC,',',IGG,',',J,') = ',
C    2                        SUMDERIV(ICC,IGG,J)
                      END IF
                  END DO
              END DO
          END DO
      END DO

C Now calculate the derivative of visibility squared.
      DO ICC = 1, NCOMP
        DO IGG = 1, NFILT
          DO J = 1, 8
            IF(VARY(ICC,IGG,J)) THEN
                V2DERIV(ICC,IGG,J) 
     1           = 2.0 * DBLE( VISTOT(ID,IG)*CONJ(SUMDERIV(ICC,IGG,J)) )
C               WRITE(OUTC,'(A,I2,A,I2,A,I2,A,G11.4)') 
C    1           ' V2DERIV(',ICC,',',IGG,',',J,') = ',V2DERIV(ICC,IGG,J)
            END IF
          END DO
        END DO
      END DO

      RETURN
      END
C======================================================================
      COMPLEX*16 FUNCTION CONJ(X)
C Complex conjugate (double precision)
      COMPLEX*16 X
      CONJ = CMPLX(DBLE(X),-DIMAG(X))
      RETURN
      END