subroutine zspace(ac11,as11,ac21,as21)
c
c Transform a variable from kz space into z space.
c
      implicit none
      include 'itg.par'
      include 'itg.cmn'
      real ac11(lz,mz,nz,nspecz),as11(lz,mz,nz,nspecz),
     * ac21(lz,mz,nzz),as21(lz,mz,nzz),
     * ar(lz*mz*nzz),ai(lz*nzz*mz)
      integer l,m,n,ifail,nmodes,index,imode
      character init*10
      data init /'Initial'/
      real trig(2*nzz)	    ! NAG workspace
      real work(2*lz*mz*nzz)     ! Nag workspace
      save init,trig
c
c For single-helicity run, skip this subroutine
c
      if(nd.eq.1) then
      do 500 m=1,md
      do 500 l=1,ldb
      ac21(l,m,1)=ac11(l,m,1,1)
      as21(l,m,1)=as11(l,m,1,1)
 500  continue
      goto 1000
      endif
c
c Initialize a couple of variables
c
      nmodes=ldb*md
c
c First, fill out the array for the FFT:
c
      do 1 m=1,md
      do 1 n=1,nddp
      do 1 l=1,ldb
      ac21(l,m,n) = ac11(l,m,n,1)
      as21(l,m,n) = as11(l,m,n,1)
 1    continue
c
      do 2 m=1,md
      do 2 n=1,nadd
      do 2 l=1,ldb
      ac21(l,m,n+nddp)=0.
      as21(l,m,n+nddp)=0.
 2    continue
c
      do 3 n=1,nddm
      do 3 m=1,md
      do 3 l=1,ldb
      ac21(l,m,n+nadd+nddp) = ac11(l,m,n+nddp,1)
      as21(l,m,n+nadd+nddp) = as11(l,m,n+nddp,1)
 3    continue
c
c Reorder the terms for NAG:
c
      imode=0
      do 300 m=1,md
      do 300 l=1,ldb
      imode=imode+1
      do 300 n=1,nalias
      index=imode+(n-1)*nmodes
      ar(index)=ac21(l,m,n)
      ai(index)=-as21(l,m,n) !c.c. for inverse FFT
 300  continue
c
c Do the FFT
c
      ifail=0
      call c06frE(nmodes,nalias,ar,ai,init,trig,work,ifail)
      init='Subsequent'
c
c Reorder the terms for my use:
c
      imode=0
      do 301 m=1,md
      do 301 l=1,ldb
      imode=imode+1
      do 301 n=1,nalias
      index=imode+(n-1)*nmodes
      ac21(l,m,n)=ar(index)*rootn
      as21(l,m,n)=-ai(index)*rootn !c.c. for inverse FFT
 301  continue
c
 1000 continue
c
      return
      end