subroutine bond_move(nbond,nstart,psi,lprint,error)
C Move NBOND fragment starting from the CA(nstart) by angle PSI.
      implicit real*8 (a-h,o-z)
      include 'DIMENSIONS'
      integer nbond,nstart
      double precision psi
      logical fail,error,lprint
      include 'COMMON.GEO'
      include 'COMMON.CHAIN'
      include 'COMMON.VAR'
      include 'COMMON.IOUNITS'
      include 'COMMON.MCM'
      dimension x(3),e(3,3),e1(3),e2(3),e3(3),rot(3,3),trans(3,3)
      error=.false.
      nend=nstart+nbond
      if (print_mc.gt.2) then
      write (iout,*) 'nstart=',nstart,' nend=',nend,' nbond=',nbond
      write (iout,*) 'psi=',psi
      write (iout,'(a)') 'Original coordinates of the fragment'
      do i=nstart,nend
        write (iout,'(i5,3f10.5)') i,(c(j,i),j=1,3)
      enddo
      endif
      if (nstart.lt.1 .or. nend .gt.nres .or. nbond.lt.2 .or. 
     & nbond.ge.nres-1) then
        write (iout,'(a)') 'Bad data in BOND_MOVE.'
        error=.true.
        return
      endif
C Generate the reference system.
      i2=nend
      i3=nstart
      i4=nstart+1
      call refsys(i2,i3,i4,e1,e2,e3,error) 
C Return, if couldn't define the reference system.
      if (error) return
C Compute the transformation matrix.
      cospsi=dcos(psi)
      sinpsi=dsin(psi)
      rot(1,1)=1.0D0
      rot(1,2)=0.0D0
      rot(1,3)=0.0D0
      rot(2,1)=0.0D0
      rot(2,2)=cospsi
      rot(2,3)=-sinpsi
      rot(3,1)=0.0D0
      rot(3,2)=sinpsi
      rot(3,3)=cospsi
      do i=1,3
        e(1,i)=e1(i)
        e(2,i)=e2(i)
        e(3,i)=e3(i)
      enddo

      if (print_mc.gt.2) then
      write (iout,'(a)') 'Reference system and matrix r:'
      do i=1,3
        write(iout,'(i5,2(3f10.5,5x))')i,(e(i,j),j=1,3),(rot(i,j),j=1,3)
      enddo
      endif

      call matmult(rot,e,trans)
      do i=1,3
        do j=1,3
          e(i,1)=e1(i)
          e(i,2)=e2(i)
          e(i,3)=e3(i)
        enddo
      enddo
      call matmult(e,trans,trans)

      if (lprint) then
      write (iout,'(a)') 'The trans matrix:'
      do i=1,3
        write (iout,'(i5,3f10.5)') i,(trans(i,j),j=1,3)
      enddo
      endif

      do i=nstart,nend
        do j=1,3
          rij=c(j,nstart)
          do k=1,3
            rij=rij+trans(j,k)*(c(k,i)-c(k,nstart))
          enddo
          x(j)=rij
        enddo
        do j=1,3
          c(j,i)=x(j)
        enddo
      enddo

      if (lprint) then
      write (iout,'(a)') 'Rotated coordinates of the fragment'
      do i=nstart,nend
        write (iout,'(i5,3f10.5)') i,(c(j,i),j=1,3)
      enddo
      endif

c     call int_from_cart(.false.,lprint)
      if (nstart.gt.1) then
        theta(nstart+1)=alpha(nstart-1,nstart,nstart+1)
        phi(nstart+2)=beta(nstart-1,nstart,nstart+1,nstart+2)
        if (nstart.gt.2) phi(nstart+1)=
     &                beta(nstart-2,nstart-1,nstart,nstart+1)
      endif
      if (nend.lt.nres) then
        theta(nend+1)=alpha(nend-1,nend,nend+1)
        phi(nend+1)=beta(nend-2,nend-1,nend,nend+1)
        if (nend.lt.nres-1) phi(nend+2)=
     &                beta(nend-1,nend,nend+1,nend+2)
      endif
      if (print_mc.gt.2) then
      write (iout,'(/a,i3,a,i3,a/)') 
     & 'Moved internal coordinates of the ',nstart,'-',nend,
     & ' fragment:'
      do i=nstart+1,nstart+2
        write (iout,'(i5,2f10.5)') i,rad2deg*theta(i),rad2deg*phi(i)
      enddo
      do i=nend+1,nend+2
        write (iout,'(i5,2f10.5)') i,rad2deg*theta(i),rad2deg*phi(i)
      enddo
      endif
      return
      end