SUBROUTINE init_advec

!--------------------------------------------------------------------------------!
! This file is part of PALM.
!
! PALM is free software: you can redistribute it and/or modify it under the terms
! of the GNU General Public License as published by the Free Software Foundation,
! either version 3 of the License, or (at your option) any later version.
!
! PALM is distributed in the hope that it will be useful, but WITHOUT ANY
! WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
! A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
!
! You should have received a copy of the GNU General Public License along with
! PALM. If not, see <http://www.gnu.org/licenses/>.
!
! Copyright 1997-2012  Leibniz University Hannover
!--------------------------------------------------------------------------------!
!
! Current revisions:
! -----------------
!
!
! Former revisions:
! -----------------
! $Id: init_advec.f90 1037 2012-10-22 14:10:22Z franke $
!
! 1036 2012-10-22 13:43:42Z raasch
! code put under GPL (PALM 3.9)
!
! 1003 2012-09-14 14:35:53Z raasch
! obsolete variables removed
!
! 1001 2012-09-13 14:08:46Z raasch
! all actions concerning upstream-spline-method removed
!
! RCS Log replace by Id keyword, revision history cleaned up
!
! Revision 1.6  2004/04/30 11:59:31  raasch
! impulse_advec renamed momentum_advec
!
! Revision 1.1  1999/02/05 09:07:38  raasch
! Initial revision
!
!
! Description:
! ------------
! Initialize constant coefficients and parameters for certain advection schemes.
!------------------------------------------------------------------------------!

    USE advection
    USE arrays_3d
    USE indices
    USE control_parameters

    IMPLICIT NONE

    INTEGER :: i, intervals, j
    REAL    :: delt, dn, dnneu, ex1, ex2, ex3, ex4, ex5, ex6, sterm


    IF ( scalar_advec == 'bc-scheme' )  THEN

!
!--    Compute exponential coefficients for the Bott-Chlond scheme
       intervals = 1000
       ALLOCATE( aex(intervals), bex(intervals), dex(intervals), eex(intervals) )

       delt  = 1.0 / REAL( intervals )
       sterm = delt * 0.5

       DO  i = 1, intervals

          IF ( sterm > 0.5 )  THEN
             dn = -5.0
          ELSE
             dn = 5.0
          ENDIF

          DO  j = 1, 15
             ex1 = dn * EXP( -dn ) - EXP( 0.5 * dn ) + EXP( -0.5 * dn )
             ex2 = EXP( dn ) - EXP( -dn )
             ex3 = EXP( -dn ) * ( 1.0 - dn ) - 0.5 * EXP(  0.5 * dn ) &
                                             - 0.5 * EXP( -0.5 * dn )
             ex4 = EXP( dn ) + EXP( -dn )
             ex5 = dn * sterm + ex1 / ex2
             ex6 = sterm + ( ex3 * ex2 - ex4 * ex1 ) / ( ex2 * ex2 )
             dnneu = dn - ex5 / ex6
             dn  = dnneu
          ENDDO

          IF ( sterm < 0.5 )  dn = MAX(  2.95E-2, dn )
          IF ( sterm > 0.5 )  dn = MIN( -2.95E-2, dn )
          ex1 = EXP( -dn )
          ex2 = EXP( dn ) - ex1
          aex(i) = -ex1 / ex2
          bex(i) = 1.0 / ex2
          dex(i) = dn
          eex(i) = EXP( dex(i) * 0.5 )
          sterm = sterm + delt

       ENDDO

    ENDIF

 END SUBROUTINE init_advec