anchor.diff:                if(ierr.ne.izero) return
   c
                 call iterate(
  -     &         alnz,pcg,zcg,ja,                                         ! sparse
  -     &         b,btot,bres,pvec,gvec1,gvec2,grav,                       ! force
  -     &         x,d,deld,dprev,dcur,id,iwink,wink,nsysdat,               ! global
  +     &         alnz,pcg,zcg,dprev,ja,                                   ! sparse
  +     &         bextern,btraction,bgravity,bconcforce,bprestress,bintern,! force
  +     &         bresid,bwork,dispvec,nforce,grav,                        ! force
  +     &         x,d,deld,dcur,id,iwink,wink,nsysdat,                     ! global
        &         dx,deldx,dxcur,idx,iwinkx,winkx,idslp,ipslp,             ! slip
        &         nfault,dfault,tfault,                                    ! fault
        &         s,stemp,                                                 ! stiff
  
positive.code:               if(ierr.ne.izero) return
  c
                call formdf_ss(
       &         b,neq,                                                   ! force
       &         x,d,dcur,numnp,                                          ! global
       &         s,stemp,                                                 ! stiff
       &         dmat,ien,lm,lmx,infiel,iddmat,ndmatsz,numelt,nconsz,     ! elemnt
  
negative.code: c
              call fill(deld,zero,ndof*numnp)
              call fill(deldx,zero,ndof*numnp)
              call fill(bextern,zero,neq*nextflag)
              call fill(btraction,zero,neq*ntractflag)
              call fill(bconcforce,zero,neq*nconcflag)
  c*            call fill(bintern,zero,neq)
              if(skc) then
                call skclear(idslp,skew,numsn,numnp)
                call skcomp(x,d,skew,idslp,ipslp,ipstrs,numsn,numnp,nstep,
  