SUBROUTINE timestep_scheme_steering

!------------------------------------------------------------------------------!
! Current revisions:
! -----------------
!
! Former revisions:
! -----------------
! $Id: timestep_scheme_steering.f90 674 2011-01-18 16:33:31Z helmke $
!
! 673 2011-01-18 16:19:48Z suehring
! No pressure term during time integration (tsc(4)=0.0).
!
! RCS Log replace by Id keyword, revision history cleaned up
!
! Revision 1.2  2005/03/26 21:17:06  raasch
! No pressure term for Runge-Kutta-schemes (tsc(4)=0.0)
!
! Revision 1.1  2004/01/28 15:34:47  raasch
! Initial revision
!
!
! Description:
! ------------
! Depending on the timestep scheme set the steering factors for the prognostic
! equations.
!------------------------------------------------------------------------------!

    USE control_parameters

    IMPLICIT NONE


    IF ( timestep_scheme(1:5) == 'runge' )  THEN
!
!--    Runge-Kutta schemes (here the factors depend on the respective
!--    intermediate step)
       IF ( timestep_scheme == 'runge-kutta-2' )  THEN
          IF ( intermediate_timestep_count == 1 )  THEN
             tsc(1:5) = (/ 1.0, 1.0,  0.0, 0.0, 0.0 /)
          ELSE
             tsc(1:5) = (/ 1.0, 0.5, -0.5, 0.0, 1.0 /)
          ENDIF
       ELSE
          IF ( intermediate_timestep_count == 1 )  THEN
             tsc(1:5) = (/ 1.0,   1.0/3.0,        0.0, 0.0, 0.0 /)
          ELSEIF ( intermediate_timestep_count == 2 )  THEN
             tsc(1:5) = (/ 1.0, 15.0/16.0, -25.0/48.0, 0.0, 0.0 /)
          ELSE
             tsc(1:5) = (/ 1.0,  8.0/15.0,   1.0/15.0, 0.0, 1.0 /)
          ENDIF          
       ENDIF

    ELSE

       IF ( .NOT. dt_fixed )  THEN
!
!--       Leapfrog and Euler schemes
!--       Determine whether after the time step adjustment the Euler- or the
!--       leapfrog scheme will be applied. The very first time step must always
!--       be an Euler step.
          IF ( dt_changed )  THEN
             IF ( timestep_scheme == 'leapfrog+euler'  .OR. &
                  timestep_scheme == 'euler' .OR. simulated_time == 0.0 )  THEN
                tsc(1:5) = (/ 1.0, 1.0, 0.0, 0.0, 1.0 /)
             ELSE
                tsc(1:5) = (/ 0.0, 2.0, 0.0, 0.0, 2.0 /)
             ENDIF
          ELSE
!
!--          No time step change, hence continue with the scheme set by the
!--          user.
             IF ( timestep_scheme == 'euler' )  THEN
                tsc(1:5) = (/ 1.0, 1.0, 0.0, 0.0, 1.0 /)
             ELSE
                tsc(1:5) = (/ 0.0, 2.0, 0.0, 0.0, 2.0 /)
             ENDIF
          ENDIF

       ELSE

!
!--       Fixed time step:
!
!--       In any case, the very first time step must always be an Euler step.
          timestep_reason = 'F'
          IF ( simulated_time == 0.0 )  THEN
             dt_changed = .TRUE.
             tsc(1:5) = (/ 1.0, 1.0, 0.0, 0.0, 1.0 /)
          ELSE
             dt_changed = .FALSE.
             IF ( timestep_scheme == 'euler' )  THEN
                tsc(1:5) = (/ 1.0, 1.0, 0.0, 0.0, 1.0 /)
             ELSE
                tsc(1:5) = (/ 0.0, 2.0, 0.0, 0.0, 2.0 /)
             ENDIF
          ENDIF

       ENDIF

    ENDIF


 END SUBROUTINE timestep_scheme_steering