subroutine abnchn(mode)
c     =======================
c
c     changing abundances (eliminating) species for an
c     evaluating an opacity table
c
      INCLUDE 'PARAMS.FOR'
      INCLUDE 'MODELP.FOR'
      common/relabu/relabn(matom),popul0(mlevel,1)
      data iread/1/
c
      if(iread.eq.1) then
         do ia=1,matom
            relabn(ia)=1.
         end do
   10    continue
         read(2,*,err=20,end=20) iatom,rela
         relabn(iatom)=rela
         write(*,*) 'ABUNDANCES CHANGED (AT.NUMBER, ABUND):',iatom,rela
         go to 10
   20    continue
         if(relabn(1).eq.0.) then
            iophmi=0
            ioph2p=0
         end if
         iread=0
      end if
c
      if(mode.eq.0) then
         do iat=1,natom
            do ii=n0a(iat),nka(iat)
               popul0(ii,1)=popul(ii,1)
            end do
         end do
         return
      end if
c
      do iat=1,natom
         ia=numat(iat)
         do ii=n0a(iat),nka(iat)
            popul(ii,1)=popul0(ii,1)*relabn(ia)
         end do
      end do
c
      do ia=1,matom
         do io=1,mion0
            rrr(1,io,ia)=rrr(1,io,ia)*relabn(ia)
         end do
      end do
c
      return
      end