subroutine oligomer
      implicit none
      include "DIMENSIONS"
      include "COMMON.CHAIN"
      include "COMMON.INTERACT"
      include "COMMON.IOUNITS"
      integer nchain,i,ii,ipi,ipj,ipmin,j,jmin,k,ix,iy,iz,
     &  ixmin,iymin,izmin
      logical newchain 
      integer ichain(2,20),iper(20),iaux
      double precision dchain,dchainmin,cmchain(3,20)
      nchain=1
      newchain=.false.
      ichain(1,nchain)=1
      do i=2,nres
        if (itype(i).eq.ntyp1) then
          if (newchain) then
            ichain(2,nchain)=i
            nchain=nchain+1
            newchain=.false.
          else 
            newchain=.true.
            ichain(1,nchain)=i
          endif
        endif   
      enddo
      ichain(2,nchain)=nres
      write (iout,*) "Chains"
      do i=1,nchain
        write (iout,*) i,ichain(1,i),ichain(2,i)
      enddo
      cmchain=0.0d0
      do i=1,nchain
        ii=0
        do j=ichain(1,i),ichain(2,i)
          if (itype(j).eq.ntyp1) cycle
          ii=ii+1
          do k=1,3
            cmchain(k,i)=cmchain(k,i)+c(k,j)
          enddo
        enddo
        do k=1,3
          cmchain(k,i)=cmchain(k,i)/ii
        enddo
      enddo
      do i=1,nchain
        iper(i)=i
      enddo
      do i=1,nchain
        dchainmin=1.0d10
        do j=i+1,nchain
          ipi=iper(i)
          ipj=iper(j)
          do ix=-1,1
            do iy=-1,1
              do iz=-1,1
                dchain=(cmchain(1,ipj)-cmchain(1,ipi)+ix*boxxsize)**2+
     &                 (cmchain(2,ipj)-cmchain(2,ipi)+iy*boxysize)**2+
     &                 (cmchain(3,ipj)-cmchain(3,ipi)+iz*boxzsize)**2
                if (dchain.lt.dchainmin) then
                  dchainmin=dchain
                  ixmin=ix
                  iymin=iy
                  izmin=iz
                  jmin=j
                endif
              enddo
            enddo
          enddo
        enddo
        cmchain(1,jmin)=cmchain(1,jmin)+ixmin*boxxsize
        cmchain(2,jmin)=cmchain(2,jmin)+iymin*boxysize
        cmchain(3,jmin)=cmchain(3,jmin)+izmin*boxzsize
        do k=ichain(1,jmin),ichain(2,jmin)
          c(1,k)=c(1,k)+ixmin*boxxsize
          c(2,k)=c(2,k)+iymin*boxysize
          c(3,k)=c(3,k)+izmin*boxzsize
        enddo
        write (iout,*) "jmin",jmin," ixmin",ixmin," iymin",iymin,
     &   " izmin",izmin
        iaux=iper(i+1)
        iper(i+1)=iper(jmin)
        iper(jmin)=iaux
      enddo
      return
      end