subroutine HexCon( mode, nnCon, nnJac, neJac, x, fCon, gCon,
     &                   nState, cu, lencu, iu, leniu, ru, lenru )

      implicit           double precision(a-h,o-z)
      double precision   x(nnJac), fCon(nnCon), gCon(neJac)

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

*     ==================================================================
*     Problem Hexagon. 
*
*     No user-defined storage is used.
*     ==================================================================
      parameter         (two   = 2.0d+0)

      fCon( 1) =    x(1)**2          +  x(6)**2
      fCon( 2) =   (x(2) - x(1))**2  +  (x(7) - x(6))**2
      fCon( 3) =   (x(3) - x(1))**2  +  x(6)**2
      fCon( 4) =   (x(1) - x(4))**2  +  (x(6) - x(8))**2
      fCon( 5) =   (x(1) - x(5))**2  +  (x(6) - x(9))**2
      fCon( 6) =    x(2)**2          +  x(7)**2
      fCon( 7) =   (x(3) - x(2))**2  +  x(7)**2
      fCon( 8) =   (x(4) - x(2))**2  +  (x(8) - x(7))**2
      fCon( 9) =   (x(2) - x(5))**2  +  (x(7) - x(9))**2
      fCon(10) =   (x(4) - x(3))**2  +  x(8)**2
      fCon(11) =   (x(5) - x(3))**2  +  x(9)**2
      fCon(12) =    x(4)**2          +  x(8)**2
      fCon(13) =   (x(4) - x(5))**2  +  (x(9) - x(8))**2
      fCon(14) =    x(5)**2          +  x(9)**2

*     Nonlinear Jacobian elements for column 1.
*     rows = (1,2,3,4,5).

      gCon( 1) =   two*x(1)
      gCon( 2) = - two*(x(2) - x(1))
      gCon( 3) = - two*(x(3) - x(1))
      gCon( 4) =   two*(x(1) - x(4))
      gCon( 5) =   two*(x(1) - x(5))

*     Nonlinear Jacobian elements for column 2.
*     Rows = (2,6,7,8,9).

      gCon( 6) =   two*(x(2) - x(1))
      gCon( 7) =   two*x(2)
      gCon( 8) = - two*(x(3) - x(2))
      gCon( 9) = - two*(x(4) - x(2))
      gCon(10) =   two*(x(2) - x(5))

*     Nonlinear Jacobian elements for column 3.
*     Rows = (3,7,10,11).

      gCon(11) =   two*(x(3) - x(1))
      gCon(12) =   two*(x(3) - x(2))
      gCon(13) = - two*(x(4) - x(3))
      gCon(14) = - two*(x(5) - x(3))
             
*     Nonlinear Jacobian elements for column 4.
*     Rows = (4,8,10,12,13).

      gCon(15) = - two*(x(1) - x(4))
      gCon(16) =   two*(x(4) - x(2))
      gCon(17) =   two*(x(4) - x(3))
      gCon(18) =   two*x(4)
      gCon(19) =   two*(x(4) - x(5))

*     Nonlinear Jacobian elements for column 5.
*     Rows = (5,9,11,13,14).

      gCon(20) = - two*(x(1) - x(5))
      gCon(21) = - two*(x(2) - x(5))
      gCon(22) =   two*(x(5) - x(3))
      gCon(23) = - two*(x(4) - x(5))
      gCon(24) =   two*x(5)

*     Nonlinear Jacobian elements for column 6.
*     Rows = (1,2,3,4,5).      

      gCon(25) =   two*x(6)
      gCon(26) = - two*(x(7) - x(6))
      gCon(27) =   two*x(6)
      gCon(28) =   two*(x(6) - x(8))
      gCon(29) =   two*(x(6) - x(9))

*     Nonlinear Jacobian elements for column 7.
*     Rows = (2,6,7,8,9).

      gCon(30) =   two*(x(7) - x(6))
      gCon(31) =   two*x(7)
      gCon(32) =   two*x(7)
      gCon(33) = - two*(x(8) - x(7))
      gCon(34) =   two*(x(7) - x(9))

*     Nonlinear Jacobian elements for column 8.
*     Rows = (4,8,10,12,13).

      gCon(35) = - two*(x(6) - x(8))
      gCon(36) =   two*(x(8) - x(7))
      gCon(37) =   two*x(8)
      gCon(38) =   two*x(8)
      gCon(39) = - two*(x(9) - x(8))

*     Nonlinear Jacobian elements for column 9.
*     Rows = (5,9,11,13,14).

      gCon(40) = - two*(x(6) - x(9))
      gCon(41) = - two*(x(7) - x(9))
      gCon(42) =   two*x(9)
      gCon(43) =   two*(x(9) - x(8))
      gCon(44) =   two*x(9)

*     end of constraints for Hexagon.
      end