subroutine flrfft(isave,ac,as,bc,bs,isign,wgt)
c
	implicit none
	include 'itg.par'
	include 'itg.cmn'

c define the arguments
	real ac(lz,mz,nz,nspecz),as(lz,mz,nz,nspecz)
	real bc(lz,mz,nz,nspecz),bs(lz,mz,nz,nspecz)

c declare local workspace
	real ar(lz*mz*nz),ai(lz*mz*nz)
	real br(lz*mz*nz),bi(lz*mz*nz)
c
	real trig(2*lz)	        ! NAG workspace
	real work(2*lz*mz*nz)	! Nag workspace
	real wgt(lz*mz*nz) ! flr weight
	integer ifail	! NAG error code
        integer isign,isave
	character init*10
	data init / 'Initial' /

c declare other local variables
	integer nmodes,imode,n,m,l,index

c ensure that some local variables are saved for future calls
	save init, trig, ar, ai

c start executable code
c********************************************************************
        nmodes=nd*md
        if(isave.eq.0) then
c reorder field for NAG's usage
	imode=0
	do 1 n=1,nd
	do 1 m=1,md
	imode=imode+1
	do 1 l=1,ld-1
	index=imode+(l-1)*nmodes
	ar(index)=ac(l,m,n,1)
	ai(index)=as(l,m,n,1)
 1    continue
c
c do Fourier Transform
c
	ifail=0
	call c06frE(nmodes,ld-1,ar,ai,init,trig,work,ifail)
	init='Subsequent'
      endif
c
c isign = 1 -> straight FFT with weight
c
        if(isign.eq.1) then
	do 2 n=1,nmodes*(ld-1)
	br(n)=ar(n)*wgt(n)
	bi(n)=-ai(n)*wgt(n)     !c.c. for inverse FFT
 2    continue
c
c isign = 2 -> use for i*wgt*field
c
        else if(isign.eq.2) then
	do 3 n=1,nmodes*(ld-1)
	br(n)=-ai(n)*wgt(n)
	bi(n)=-ar(n)*wgt(n)     !c.c. for inverse FFT
 3    continue
c
c isign = 4 -> use for field*abs(k)
c
        else if(isign.eq.4) then
	do 4 n=1,nmodes*(ld-1)
	br(n)=ar(n)*abs(wgt(n))
	bi(n)=-ai(n)*abs(wgt(n)) !c.c. for inverse FFT
 4    continue
      endif
c     
	call c06frE(nmodes,ld-1,br,bi,init,trig,work,ifail)
c
c reorder
c
	imode=0
	do 10 n=1,nd
	do 10 m=1,md
	imode=imode+1
	do 10 l=1,ld-1
	index=imode+(l-1)*nmodes
	bc(l,m,n,1)=br(index)
	bs(l,m,n,1)=-bi(index)	!c.c. for inverse FFT
 10   continue
c
c enforce b.c.'s if necessary
c
      if(isign.eq.1) call bcon(bc,bs,1,0)
c
	return
	end