C GRADIG    SOURCE    AM        11/05/26    21:15:36     6982           
      subroutine GRADIG (da, force, q, force_prec, Xkapai,
     & Xksii, Xkapa_prec, Xksi_prec, Gradgs, Xkapa, Xksi)
C     Routine permettant le calcul des dérivées de la loi d'écoulement par rapport à l'effort et au vecteur force et d'écrouissage

        IMPLICIT INTEGER(I-N)
        IMPLICIT REAL*8(A-H,O-Z)
        DIMENSION da(20), force(5), q(5), force_prec(5)
        DIMENSION Gradgs(5), Xk19(4), term_Gradgs1(4)
*
        a=da(8)
        b=da(9)
        c=da(10)
        d=da(11)
        e=da(12)
        f=da(13)

        gamma=1
        gamma_prec=1

        if (force(1).le.0) then
        den1=0
        den2=0
        else
        den1=q(5)*a*((force(1))**c)*((gamma-force(1))**d)
        den2=q(5)*b*((force(1))**e)*((gamma-force(1))**f)
        endif

        Xk11 = force(2)/den1
        Xk12 = force(3)/den2
        Xk13 = force(4)/den1
        Xk14 = force(5)/den2

        Xk15 = q(1)/q(5)
        Xk16 = q(2)/q(5)
        Xk17 = q(3)/q(5)
        Xk18 = q(4)/q(5)
        Xk19(1) = Xk11-Xk15
        Xk19(2) = Xk12-Xk16
        Xk19(3) = Xk13-Xk17
        Xk19(4) = Xk14-Xk18
*
        term_Gradgs1(1) = Xk19(1)*force(2)*d/den1*
     & (2*force(1)-gamma*(1-Xkapai))/
     & ((gamma-force(1))*(Xkapai*gamma+force(1)))
        term_Gradgs1(2) = Xk19(2)*force(3)*f/den2*
     & (2*force(1)-gamma*(1-Xksii))/
     & ((gamma-force(1))*(Xksii*gamma+force(1)))
        term_Gradgs1(3) = Xk19(3)*force(4)*d/den1*
     & (2*force(1)-gamma*(1-Xkapai))/
     & ((gamma-force(1))*(Xkapai*gamma+force(1)))
        term_Gradgs1(4) = Xk19(4)*force(5)*f/den2*
     & (2*force(1)-gamma*(1-Xksii))/
     & ((gamma-force(1))*(Xksii*gamma+force(1)))

        if (force_prec(1).le.gamma_prec*(1-Xkapai)/2) then
        term_Gradgs1(1)=0
        term_Gradgs1(3)=0
        Xkapa=1-2*force_prec(1)/gamma_prec
                if (Xkapa.lt.Xkapa_prec) then
*pour empêcher Xkapa de diminuer
                Xkapa=Xkapa_prec 
                endif
        else
        Xkapa=Xkapai
        endif

        if (force_prec(1).le.gamma_prec*(1-Xksii)/2) then
        term_Gradgs1(2)=0
        term_Gradgs1(4)=0
        Xksi=1-2*force_prec(1)/gamma_prec
                if (Xksi.lt.Xksi_prec) then
*pour empêcher Xksi de diminuer
                Xksi=Xksi_prec
                endif
        else
        Xksi=Xksii
        endif


        Gradgs(1) = abs(2*(term_Gradgs1(1)+term_Gradgs1(2)+
     & term_Gradgs1(3)+term_Gradgs1(4)))
        Gradgs(2) = 2*Xk19(1)/den1
        Gradgs(3) = 2*Xk19(2)/den2
        Gradgs(4) = 2*Xk19(3)/den1
        Gradgs(5) = 2*Xk19(4)/den2
*
C       Gradgs(1) =0
        call SCALPR(5,Gradgs,Gradgs,Xnorm_Gradgs)
        Xnorm_Gradgs=sqrt(Xnorm_Gradgs)
      DO I=1,5 
        Gradgs(I)=Gradgs(I)/Xnorm_Gradgs
      ENDDO
        return
        end