C GRADIF    SOURCE    AM        11/05/26    21:15:35     6982           
      SUBROUTINE GRADIF (da, force, q, Gradfs, Gradfq)
C     Routine permettant le calcul des dérivées de la surface de charge 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),Gradfs(5),Gradfq(5),Xk9(4)
*
        a=da(8)
        b=da(9)
        c=da(10)
        d=da(11)
        e=da(12)
        f=da(13)

        gamma=1.
        if (force(1).le.0) then
        Xnum1=0
        Xnum2=0
        else
        Xnum1=((force(1))**c)*((gamma-force(1))**d)
        Xnum2=((force(1))**(c-e))*((gamma-force(1))**(d-f))
        endif
        Xk1 = force(2)/a
        Xk2 = force(3)*Xnum2/b
        Xk3 = force(4)/a
        Xk4 = force(5)*Xnum2/b
        Xk5 = q(1)*Xnum1
        Xk6 = q(2)*Xnum1
        Xk7 = q(3)*Xnum1
        Xk8 = q(4)*Xnum1

        Xk9(1)=Xk1-Xk5
        Xk9(2)=Xk2-Xk6
        Xk9(3)=Xk3-Xk7
        Xk9(4)=Xk4-Xk8

        if (force(1).le.0) then
        Xnum3=0
        Xnum4=0
        else
        Xnum3 =  c*((force(1))**(c-1))*((gamma-force(1))**d)
     & -d*((force(1))**c)*((gamma-force(1))**(d-1))
        Xnum4 =(c-e)*((force(1))**(c-e-1))*((gamma-force(1))**(d-f))
     & -(d-f)*((force(1))**(c-e))*((gamma-force(1))*(d-f-1))
        endif

        Gradfs(1) = -2*(Xk9(1)*q(1)*Xnum3-Xk9(2)
     & *(force(3)/b*Xnum4-q(2)*Xnum3) + Xk9(3)*q(3)*Xnum3
     & -Xk9(4)*(force(5)/b*Xnum4-q(4)*Xnum3)
     & +q(5)**2*Xnum1*Xnum3)

        Gradfs(2) = 2*Xk9(1)/a
        Gradfs(3) = 2*Xk9(2)*Xnum2/b
        Gradfs(4) = 2*Xk9(3)/a
        Gradfs(5) = 2*Xk9(4)*Xnum2/b

        if (force(1).le.0) then
        Xnum5=0
        Xnum6=0
        else
        Xnum5=((force(1))**c)*((gamma-force(1))**(d-1))
        Xnum6=((force(1))**(c-e))*((gamma-force(1))**(d-f-1))
        endif

        Gradfq(1) = -2*Xk9(1)*Xnum1
        Gradfq(2) = -2*Xk9(2)*Xnum1
        Gradfq(3) = -2*Xk9(3)*Xnum1
        Gradfq(4) = -2*Xk9(4)*Xnum1
        Gradfq(5) = -2*q(5)*Xnum1**2

        return
        end