subroutine flat3(savg0,iz,nterms,ynoise,savg)

  implicit real*8 (a-h,o-z)
  parameter (NSMAX=6827)
  real*4 savg0(iz)
  real*4 savg(iz)
  real*4 ynoise,y4

  real*8 x(NSMAX)
  real*8 y(NSMAX)
  real*8 y0(NSMAX)
  real*8 yfit(NSMAX)
  real*8 a(10)
  integer ii(NSMAX)

  npts0=999999
  df=12000.0/16384.0

  do i=1,iz
     y0(i)=db(savg0(i))
  enddo
  ia=200.0/df
  ib=4500.0/df
  j=0
  do i=ia,ib
     j=j+1
     x(j)=i*df
     y(j)=y0(i)
     ii(j)=i
  enddo

  npts=j
  mode=0
  a=0.0

  do iter=1,99
     call polfit(x,y,y,npts,nterms,mode,a,chisqr)
!     print*,iter,npts,a(1:nterms)

     rewind 21
     do i=1,ib
        f=i*df
        yfit(i)=0.0
        do n=1,nterms
           yfit(i)=yfit(i) + a(n) * f**(n-1)
        enddo
!        write(21,1010) f,y0(i),yfit(i),y0(i)-yfit(i)
!1010    format(4f12.3)
     enddo
     k=0
     do j=1,npts
        y1=y(j)-yfit(ii(j))
        if(y1.lt.ynoise) then
           k=k+1
           x(k)=x(j)
           y(k)=y(j)
           ii(k)=ii(j)
        endif
     enddo
     npts=k
     if(npts.eq.npts0 .or. npts.lt.(ib-ia)/10) exit
     npts0=npts
  enddo

!  do j=1,npts
!     write(22,1010) x(j),y(j),yfit(ii(j)),y(j)-yfit(ii(j))
!  enddo

  do i=1,ib
     y4=y0(i)-yfit(i)
     savg(i)=10.0**(0.1*y4)
  enddo

end subroutine flat3