subroutine SprCon( mode, m, n, njac, x, f, g, nState, 
     $                   cu, lencu, iu, leniu, ru, lenru )

      implicit           double precision (a-h,o-z)
      double precision   x(n), f(m), g(njac)

      character*8        cu(lencu)
      integer            iu(leniu)
      double precision   ru(lenru)  

*     ------------------------------------------------------------------
*     This is funcon for problem Spring  (Optimal Control Problem).
*     The Jacobian is upper bidiagonal,
*     and only the diagonal terms are nonlinear.
*     The constant 1's in the Jacobian are not regenerated here.
*     ------------------------------------------------------------------
      integer            T
      parameter        ( one = 1.0d+0 )

      T     = n - 1
      jy    =     0    ! Counts y(t) variables
      jg    =   - 1    ! Counts nonlinear Jacobian elements

      do 150, i = 1, T
         jy     = jy + 1
         jg     = jg + 2
         yt     = x(jy)
         ytp1   = x(jy + 1)
         f(i)   = 0.01d+0 * yt**2  +  (ytp1  -  yt)
         g(jg)  = 0.02d+0 * yt               -  one
*--      g(jg+1)= one      ! Constant element set by spdata.
  150 continue

*     end of constraints for Spring
      end