subroutine umatl1(eps,theta,td,d,ud,hn,h1,nh,ii,istrt, sig,dd,isw)

c-----[--.----+----.----+----.-----------------------------------------]
c     Modification log                                Date (dd/mm/year)
c       Original version                                    01/11/2006
c-----[--.----+----.----+----.-----------------------------------------]
c     Purpose: User Constitutive Model: Microsphere model of rubber
c     elasticity (C. Miehe, S. Goektepe, F. Lulei, 2003)

c     Input:
c          eps(3,3)-  Deformation gradient at point (finite deformation)
c          theta   -  Determinant of deforamtion gradient
c          td      -  Temperature change
c          d(*)    -  Program material parameters (ndd)
c          ud(*)   -  User material parameters (nud)
c          hn(nh)  -  History terms at point: t_n
c          h1(nh)  -  History terms at point: t_n+1
c          nh      -  Number of history terms
c          ii      -  Current point number
c          istrt   -  Start state: 0 = elastic; 1 = last solution
c          isw     -  Solution option from element

c     Output:
c          sig(*)  -  Stresses at point.
c                     N.B. 1-d models use only sig(1)
c          dd(6,*) -  Current material tangent moduli
c                     N.B. 1-d models use only dd(1,1) and dd(2,1)
c-----[--.----+----.----+----.-----------------------------------------]
      implicit none

      integer  nh,istrt,isw, ii,i,j
      real*8   td,fb(3,3),eps(3,3)
      real*8   theta,d(*),ud(6),hn(nh),h1(nh),sig(6),dd(6,6)

c     Compute and output stress (sig) and moduli (dd)

      call pzero(fb,9)

      do i = 1,3
       do j = 1,3
        fb(i,j) = (theta**(-1./3.))*eps(i,j)
       end do
      end do
  
      call microsphere(ud,fb,theta,sig,dd)

      end