C DDSIGGC   SOURCE    CB215821  25/04/08    21:15:09     12227          
      SUBROUTINE ddsiggc(sigma,d2gc,ag,P2,pi2,i1,i6,fc,fb,lcp)

c     This subroutine calculates the second derivative of the plastic potential in compression
c
c     Plastic potential: gc = SQRT(3 J2) + ag I1  with  J2 : 2nd invariant of the deviatoric stress
c                                                   and   I1 : 1st invariant of the stress

      IMPLICIT REAL*8 (A-B,D-H,O-Z)
      implicit integer (I-K,M,N)
      implicit logical (L)
      implicit character*10 (C)

      dimension vloc(6),vloc1(1),pi2(6),vloc2(1,6)
      dimension d2gc(6,6),p2(i6,i6),sigma(6),vloc6(6,6)

      r1 = 1.
      r2 = 2.

      do jloc=1,6
        do iloc=1,6
          d2gc(iloc,jloc) = 0.d0
        enddo
      enddo
      call mulAB(P2,sigma,vloc,6,6,6,1)
      call mulATB(sigma,vloc,vloc1,6,1,6,1)
      rloc = 0.5d0 * vloc1(1)
      if (rloc.le.0.d0) then
        psi2 = 0.d0
      else
        psi2 = SQRT(rloc)
      endif
      call mulATB(sigma,P2,vloc2,6,1,6,6)
      call mulAB(vloc,vloc2,vloc6,6,1,1,6)
      test = ag*(sigma(1)+sigma(2)+sigma(3))
      psi2lim=max(1.D-7*test,1.d-3)
      if (ABS(psi2).le.psi2lim) then
        continue
c       d2gc = 0
      else
        do jloc=1,6
          do iloc=1,6
            d2gc(iloc,jloc)=(P2(iloc,jloc)/(2.0d0*psi2))
     .                     - (vloc6(iloc,jloc)/(4.0d0*psi2*psi2*psi2))
          enddo
        enddo
      endif

      RETURN
      END