anchor.diff:        real*8 xe,dfdnx,dfdagrx,dfdtaux
   *     ***** local declarations *****
         real*8 n_13,n_23,n_53,n_83,inv_n,agr2,tauW,tauU
  +      real*8 dtauW_dn,dtauW_dagr,dtauU_dn
         real*8 p,p_14,dp_dn,dp_dagr
         real*8 z,z2,fz,dz_dn,dz_dagr,dz_dtau
         real*8 alpha,dalpha_dn,dalpha_dagr,dalpha_dtau
  
positive.code:       inv_n = 1.0d0/n
        agr2  = agr*agr
  
        p       =  agr2/(4.0d0*P23*n_83)
        p_14    =  dsqrt(dsqrt(1.0d0/(4.0d0*P23)))*dsqrt(agr)/n_23 
        dp_dn   = -etthrd*p*inv_n
        dp_dagr =  2.0d0*p/agr
  c     dp_dtau =  0.0d0
  
negative.code:       real*8 exp1,exp2,exp3,exp4,exp5
        real*8 x1,x2,x,dx1_dp,dx2_dp,dx_dp,dx_dalpha
        real*8 denh1x,numh1x,h1x,dh1x_dx,dh1x_dp,dh1x_dalpha
        real*8 gx,dgx_dp,dgx_dn,dgx_dagr
        real*8 fxa,dfxa_dalpha
        real*8 Fx,dFx_dp,dFx_dalpha,dFx_dn,dFx_dagr,dFx_dtau
        real*8 ex0,nex0
  