c force4.f
c calculate the forces involved

c force4(n,gc,ntime)
c 
c /ischeme/ icircular=1 circular 
c          iele=1  electrostatic
c          ihydro=1  hydro
c          common/ischeme/icircular,iele,ihydro,iclose
c     +neuler
c use these parameters to decide which forces need to be included
c fs,fb in force.f   fe in force_electro.f  fb in force_tor.f
c gc(maxn) using to store the force vector

	subroutine force4(n,gc,ntime)
	
	implicit double precision(a-h, o-z)
        parameter(maxa=500,maxn=maxa*3)
 	double precision gc(maxn)
          common/ischeme/icircular,iele,ihydro,iclose,iknot
     +,neuler

          	
c use noele to judge if calculate the elctrostatic force or not
	 n3=3*n
	 do i=1,n3
	    gc(i)=0.d0
	 enddo
	
	if (iele.eq.1) then
	  if (icircular.eq.1) then
          call force_electro_circular(n,gc,ntime)
	  else 
	     call force_electro_linear(n,gc,ntime)
	  endif
	endif

c       add the stretching and bending forces
        if (icircular.eq.1) then
 	  call force_circular(n,gc,ntime)
	else
	  call force_linear(n,gc,ntime)
	endif
	
c torsional force for closed circular DNA
        if ((icircular.eq.1).and.(iclose.eq.1)) then
          call force_tor(n,gc,ntime)
        endif 

        return 
        end