subroutine uel(rhs,amatrx,svars,energy,ndofel,nrhs,nsvars,
     1     props,nprops,coords,mcrd,nnode,u,du,v,a,jtype,time,
     2     dtime,kstep,kinc,jelem,params,ndload,jdltyp,adlmag,
     3     predef,npredf,lflags,mlvarx,ddlmag,mdload,pnewdt,
     4     jprops,njprop,period)
c     
      include 'aba_param.inc'
      parameter ( zero = 0.d0, half = 0.5d0, one = 1.d0 )
c
c		This is a linear truss element for Abaqus/Standard
c		general static analysis in 1D space (aligned to x-axis) only.
      dimension rhs(mlvarx,*),amatrx(ndofel,ndofel),
     1     svars(nsvars),energy(8),props(*),coords(mcrd,nnode),
     2     u(ndofel),du(mlvarx,*),v(ndofel),a(ndofel),time(2),
     3     params(3),jdltyp(mdload,*),adlmag(mdload,*),
     4     ddlmag(mdload,*),predef(2,npredf,nnode),lflags(*),
     5     jprops(*)
c
c		assign section properties
		area = props(1)
		e    = props(2)
		anu  = props(3)
		rho  = props(4)	 
c		calculate stiffness and mass
		alen = abs(coords(1,2)-coords(1,1))
		ak   = area*e/alen
		am   = half*area*rho*alen	  
c		Initialize Arrays
		rhs = zero
		amatrx = zero		
		if (lflags(3).eq.1) then
C      Stiffness and Force
C			Get Stiffness Matrix
			amatrx(1,1) =  ak  
			amatrx(4,4) =  ak  
			amatrx(1,4) = -ak  
			amatrx(4,1) = -ak
c			Get Internal Contrib to Residual Force			
            rhs(1,1) = -ak*(u(1)-u(4))
            rhs(4,1) = -ak*(u(4)-u(1))
c			Get External Contrib to Residual Force			
            do kdload = 1, ndload
              if (jdltyp(kdload,1).eq.1001) then
                rhs(4,1)  = rhs(4,1)+adlmag(kdload,1)
              end if
            end do
		else if (lflags(3).eq.2) then
c      	 	Stiffness
			amatrx(1,1) =  ak  
			amatrx(4,4) =  ak  
			amatrx(1,4) = -ak  
			amatrx(4,1) = -ak
		else if (lflags(3).eq.4) then
c       	Mass 
			do k1 = 1, ndofel
			  amatrx(k1,k1) = am
			end do
		else if (lflags(3).eq.5) then
			print *,'oops'
		else if (lflags(3).eq.6) then
C       	Mass and Force
			do k1 = 1, ndofel
				amatrx(k1,k1) = am
			end do
			rhs(1,1) = -ak*(u(1)-u(4))
			rhs(4,1) = -ak*(u(4)-u(1))
		END IF
c
      return
      end