C
C  User subroutine to define a user-defined interfacial
C  constitutive behavior

      subroutine uinter(stress,ddsddr,amki,amski,flux,ddfddt,ddsddt,
     1       ddfddr,statev,sed,sfd,spd,svd,scd,pnewdt,rdisp,drdisp,
     2       temp,dtemp,predef,dpred,time,dtime,freqr,ciname,slname,
     3       msname,props,coords,aLocalDir,drot,area,chrLngth,node,ndir,
     4       nstatv,npred,nprops,mcrd,kstep,kinc,kit,linper,lOpenClose,
     5       lState,lSdi,lPrint)
C
      include 'aba_param.inc'
C
      dimension stress(ndir),ddsddr(ndir,ndir),flux(2),ddfddt(2,2),
     $     ddsddt(ndir,2),ddfddr(2,ndir),statev(nstatv),rdisp(ndir),
     $     drdisp(ndir),temp(2),dtemp(2),predef(2,npred),dpred(2,npred),
     $     time(2),props(nprops),coords(mcrd),aLocalDir(mcrd,mcrd),
     $     drot(2,2),amki(ndir,ndir),amski(ndir,ndir)
      character*80 ciname,slname,msname
C
      flux(1) = -props(1)*(temp(1)-temp(2))
      flux(2) = -flux(1)
C
      ddfddt(1,1) = props(1)
      ddfddt(1,2) = -props(1)
      ddfddt(2,1) = -props(1)
      ddfddt(2,2) = props(1)
C
      return
      end