*CMZ :          23/08/93  13.30.11  by  Jonathan Butterworth
*-- Author :
      SUBROUTINE BFGS (N,NADIM,AHESS,EPSMCH,G,GNEW,P,ALPHA,Y)
      INTEGER N, NADIM
      DOUBLE PRECISION EPSMCH, ALPHA
      DOUBLE PRECISION AHESS(NADIM, N), G(N), GNEW(N), P(N), Y(N)
      INTEGER I, IFAIL, IP1, J, NM1
      DOUBLE PRECISION CONST, DVDOT, GTP, YTP
      SAVE
      DO 10 I=1,N
      Y(I)=GNEW(I)-G(I)
 10   CONTINUE
      YTP=DVDOT(N,Y,P)
      IF(YTP.LE.0.0D+0) RETURN
      GTP=DVDOT(N,G,P)
      CONST=ALPHA*YTP
      IF(CONST.LT.1.0D-10) RETURN
      CONST=1.0D+0/CONST
      CALL MODCHL(N,NADIM,AHESS,CONST,Y,IFAIL)
      IF(GTP.GE.0.0D+0) RETURN
      CONST=1.0D+0/SQRT(-GTP)
      DO 20 I=1,N
      Y(I)=G(I)*CONST
 20   CONTINUE
      CALL NMDCHL(N,NADIM,AHESS,EPSMCH,Y,P)
      NM1=N-1
      IF(NM1.EQ.0) RETURN
      DO 40 I=1,NM1
      IP1=I+1
      DO 30 J=IP1,N
      AHESS(I,J)=AHESS(J,I)
 30   CONTINUE
 40   CONTINUE
      RETURN
      END