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!Environment Canada - Atmospheric Science and Technology License/Disclaimer,
!                     version 3; Last Modified: May 7, 2008.
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!
!
!  X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X
!

      subroutine settrilax(pa,pb,pc,palpha,pbeta,cdgrid,kfi) 1
!
!**s/r settrila  - Prepares matrices a,b,c fro cyclic tridiagonal solver.
!
!
!Author  : Luc Fillion - MSC - 10 March 04.
!Revision: 27 sept 2004. Mu version.
!Revision: 18 Oct 2004. - Bi-periodic Arakawa-C:
!                         Scalar or PSI/ETA grid options.
!Revision: 29 May 2007. - Introduce arrays atri,btri,ctri to be kept once and for all in comdeck.
!     -------------------
!
!Arguments
!
      IMPLICIT NONE
!
#include "taglam4d.cdk"
#include "comdim.cdk"
#include "comcst.cdk"
#include "comgrd_param.cdk"
#include "comgemla.cdk"
!
      character*1 cdgrid
      integer kfi
      real*8 palpha,pbeta
      real*8 pa(nj),pb(nj),pc(nj)
!
      logical lldirichlet
      integer ji,jj,jk,jfi
      real*8 zdlon,zdlat,zdlon2,zdlat2,zalpha,zbeta,za,zra2,zcon
      real*8 zdenom,zdenom2,zratio
      real*8 zdenoma,zdenomc
      real*8 zpm(nfi)
!
!!
!
      lldirichlet=.false.
      zdlon=rdlon_an(1,1)
      zdlat=rdlat_an(1,1)
      zdlon2=zdlon*zdlon
      zdlat2=zdlat*zdlat
      zra2=ra**2
!
!     Build vectors a,b,c of tridiagonal matrix
!
      do jfi=1,nfi
        zratio=real(jfi-1)/real(ni)
        zpm(jfi)=2.0*(cos(2.*rpi*zratio)-1.)/(zdlon2)
      enddo
!
      do jj=1,nj
        if(cdgrid.eq.'S') then
          zdenoma=zra2*rdmu(jj-1)*rdmuh(jj-1)
          atris(jj)=r1mmu2h(jj-1)/zdenoma
          pa(jj) = atris(jj)
          zdenomc=zra2*rdmu(jj)*rdmuh(jj-1)
          ctris(jj)=r1mmu2h(jj)/zdenomc
          pc(jj) = ctris(jj)
          zdenom2=zra2*r1mmu2(jj)
          do jfi=1,nfi
            btris(jj,jfi)=-(atris(jj)+ctris(jj))+zpm(jfi)/zdenom2
          enddo
          pb(jj) = btris(jj,kfi)
        else
          zdenoma=zra2*rdmu(jj)*rdmuh(jj-1)
          atrip(jj)=r1mmu2(jj)/zdenoma
          pa(jj) = atrip(jj)
          zdenomc=zra2*rdmu(jj)*rdmuh(jj)
          ctrip(jj)=r1mmu2(jj+1)/zdenomc
          pc(jj) = ctrip(jj)
          zdenom2=zra2*r1mmu2h(jj)
          do jfi=1,nfi
            btrip(jj,jfi)=-(atrip(jj)+ctrip(jj))+zpm(jfi)/zdenom2
          enddo
          pb(jj) = btrip(jj,kfi)
        endif
      enddo
!
      if(lldirichlet) then
        palpha=0.
        pbeta=0.
      else
        pbeta=pa(1)
        palpha=pbeta
!        palpha=pc(nj)
!        print *,'settrila: palpha, pbeta =', palpha, pbeta
      endif
!
      return
      end