chem/KPP/kpp/kpp-2.1/int/oldies/qssafix.f

   1 C --- Plain QSSA with fixed step size
   2 C
   3       SUBROUTINE INTEGRATE( TIN, TOUT  )
   4
   5       INCLUDE 'KPP_ROOT_params.h'
   6       INCLUDE 'KPP_ROOT_global.h'
   7
   8 C TIN - Start Time
   9       KPP_REAL TIN
  10 C TOUT - End Time
  11       KPP_REAL TOUT
  12
  13 C Local variables
  14       KPP_REAL P_VAR(NVAR), D_VAR(NVAR)
  15       LOGICAL IsReject
  16       KPP_REAL T, Tnext, STEP, Told, SUP
  17       KPP_REAL ratio, tmp
  18       INTEGER i
  19
  20       T = TIN
  21       Tnext = TOUT
  22       STEP = 0.1
  23       Told = T
  24       SUP  = 1e-14
  25       IsReject = .false.
  26
  27 C -- BELOW THIS LIMIT USE TAYLOR INSTEAD OF EXP ---
  28
  29       do while ( T.lt.Tnext )
  30
  31         if ( T.gt.Tnext ) then
  32           STEP = Tnext - Told
  33           T = Tnext
  34         end if
  35
  36         CALL FSPLIT_VAR ( VAR,  P_VAR, D_VAR )
  37
  38         do i=1,NVAR
  39           if ( abs(D_VAR(i)).gt.SUP ) then
  40             ratio = P_VAR(i)/D_VAR(i)
  41             tmp = exp(-D_VAR(i)*STEP)
  42             VAR(i) = tmp * (VAR(i) - ratio) + ratio
  43           else
  44             tmp = D_VAR(i) * STEP
  45             VAR(i) = VAR(i) + P_VAR(i) * 0.5 * STEP * ( 1 - 0.5 * tmp *
  46      *             ( 1 - 1.0 / 3.0 * tmp ) )
  47           end if
  48         end do
  49
  50         T = T + STEP
  51         TIME = T
  52
  53       end do
  54
  55       RETURN
  56       END