constraint_eqn_028 Subroutine

   subroutine constraint_eqn_028(tmp_cc, tmp_con, tmp_err, tmp_symbol, tmp_units)
      !! Equation for fusion gain (big Q) lower limit
      !! author: P B Lloyd, CCFE, Culham Science Centre
      !! args : output structure : residual error; constraint value;
      !! residual error in physical units; output string; units string
      !! Equation for fusion gain (big Q) lower limit
      !! #=# physics
      !! #=#=# fqval, bigqmin
      !! and hence also optional here.
      !! Logic change during pre-factoring: err, symbol, units will be assigned only if present.
      !! fqval : input real : pf-value for Q
      !! bigq : input real : Fusion gain; P_fusion / (P_injection + P_ohmic)
      !! bigqmin : input real : minimum fusion gain Q
      !! ignite : input integer : switch for ignition assumption:<UL>
      !! <LI> = 0 do not assume plasma ignition;
      !! <LI> = 1 assume ignited (but include auxiliary power in costs)</UL>
      !! Obviously, ignite must be zero if current drive is required.
      !! If ignite=1, any auxiliary power is assumed to be used only
      !! during plasma start-up, and is excluded from all steady-state
      !! power balance calculations.
      use constraint_variables, only: fqval, bigqmin
      use current_drive_variables, only: bigq
      use physics_variables, only: ignite
      implicit none
            real(dp), intent(out) :: tmp_cc
      real(dp), intent(out) :: tmp_con
      real(dp), intent(out) :: tmp_err
      character(len=1), intent(out) :: tmp_symbol
      character(len=10), intent(out) :: tmp_units

      ! if plasma is not ignited ...
      if (ignite == 0) then
         tmp_cc =  1.0D0 - fqval * bigq/bigqmin
         tmp_con = bigqmin * (1.0D0 - tmp_cc)
         tmp_err = bigqmin * tmp_cc
         tmp_symbol = '>'
         tmp_units = ''
      ! if plasma is ignited report error
      else
         tmp_cc = 0
        tmp_con = 0
        tmp_err = 0
        tmp_symbol = ''
        tmp_units = ''
         call report_error(4)
      end if

   end subroutine constraint_eqn_028