subroutine H_TRACK_FIT(ABORT,err,ierr)
*     primary track fitting routine for the HMS spectrometer
*
*     Called by H_TRACK
*
*     d.f. geesaman         17 January 1994
*     modified 
*                           17 Feb 1994        dfg
*                              remove minuit. Make fit linear
*                              still does not do errors properly
* $Log: h_track_fit.f,v $
* Revision 1.3  1994/08/18 02:45:53  cdaq
* (DM) Add calculation of residuals
*
* Revision 1.2  1994/02/22  05:25:00  cdaq
* (SAW) Remove dfloat calls with floating args
*
* Revision 1.1  1994/02/19  06:20:53  cdaq
* Initial revision
*
*
      implicit none
      include "gen_data_structures.cmn"
      include "hms_tracking.cmn"
      include "hms_geometry.cmn"
      external H_DPSIFUN
*
*
*     local variables
*
      logical ABORT
      character*50 here
      parameter (here='H_TRACK_FIT')
      character*(*) err
      integer*4 itrack                        ! track loop index
      integer*4 ihit,ierr
      integer*4 hit,plane
      integer*4 i,j                             ! loop index
      real*8   H_DPSIFUN
      real*8   pos
      real*4   ray(hnum_fpray_param)
      real*8   ray1(4)
      real*8   ray2(4)
      real*8 TT(hnum_fpray_param)
      real*8 AA(hnum_fpray_param,hnum_fpray_param)
      real*8 dray(hnum_fpray_param)
      real*8 error(hnum_fpray_param)
      real*4 chi2,dummychi2
      parameter (dummychi2 = 1.E4)
*     array to remap hplane_coeff to param number
      integer*4 remap(hnum_fpray_param)
      data remap/5,6,3,4/
      save remap
*
      ABORT= .FALSE.
      ierr=0
*  initailize residuals

      do itrack=1,HNTRACKS_MAX
        do plane=1,HMAX_NUM_DC_PLANES
          hdc_residual(itrack,plane)=1000
          hdc_sing_res(itrack,plane)=1000
        enddo
      enddo


*     test for no tracks
      if(HNTRACKS_FP.ge.1) then
        do itrack=1,HNTRACKS_FP
          chi2= dummychi2
          htrack_fit_num=itrack

*     are there enough degrees of freedom
          HNFREE_FP(itrack)=HNTRACK_HITS(itrack,1)-hnum_fpray_param
          if(HNFREE_FP(itrack).gt.0) then

*     initialize parameters
           do i=1,hnum_fpray_param
            TT(i)=0.
            do ihit=2,HNTRACK_HITS(itrack,1)+1
              hit=HNTRACK_HITS(itrack,ihit)
              plane=HDC_PLANE_NUM(hit)
              TT(i)=TT(i)+((HDC_WIRE_COORD(hit)*
     &          hplane_coeff(remap(i),plane))
     &          /(hdc_sigma(plane)*hdc_sigma(plane)))
            enddo 
           enddo
          do i=1,hnum_fpray_param
           do j=1,hnum_fpray_param
           AA(i,j)=0.
            do ihit=2,HNTRACK_HITS(itrack,1)+1
              hit=HNTRACK_HITS(itrack,ihit)
              plane=HDC_PLANE_NUM(hit)
              AA(i,j)=AA(i,j) + (
     &           hplane_coeff(remap(i),plane)*hplane_coeff(remap(j),plane)
     &          /(hdc_sigma(plane)*hdc_sigma(plane)))
            enddo               ! end loop on ihit
           enddo                ! end loop on j
          enddo                 ! end loop on i
*
*     solve four by four equations
         call solve_four_by_four(TT,AA,dray,ierr)
*
      if(ierr.ne.0) then
         dray(1)=10000.
         dray(2)=10000.
         dray(3)=2.
         dray(4)=2.
      else
*      calculate chi2
        chi2=0.

        ray(1)=dray(1)
        ray(2)=dray(2)
        ray(3)=dray(3)
        ray(4)=dray(4)
         do ihit=2,HNTRACK_HITS(itrack,1)+1
              hit=HNTRACK_HITS(itrack,ihit)
              plane=HDC_PLANE_NUM(hit)

* note chi2 is single precision
           hdc_sing_res(itrack,plane)=
     &         (HDC_WIRE_COORD(hit)
     &         -hplane_coeff(remap(1),plane)*ray(1)
     &         -hplane_coeff(remap(2),plane)*ray(2)
     &         -hplane_coeff(remap(3),plane)*ray(3)
     &         -hplane_coeff(remap(4),plane)*ray(4))
           chi2=chi2+((hdc_sing_res(itrack,plane))**2
     &         )/(hdc_sigma(plane)*hdc_sigma(plane))

        enddo
      endif

           HX_FP(itrack)=ray(1)
           HY_FP(itrack)=ray(2)
           HZ_FP(itrack)=0.                   ! z=0 of tracking.
           HXP_FP(itrack)=ray(3)
           HYP_FP(itrack)=ray(4)
          endif                               ! end test on degrees of freedom
          HCHI2_FP(itrack)=chi2
        enddo                                 ! end loop over tracks
      endif

* calculate residuals for each chamber if in single stub mode
* and there were 2 tracks found one in first chanber and one in the second

      if (hsingle_stub.ne.0) then
        if (HNTRACKS_FP.eq.2) then
          itrack=1
          ihit=2
          hit=HNTRACK_HITS(itrack,ihit)
          plane=HDC_PLANE_NUM(hit)
          if (plane.le.6) then
            itrack=2
            hit=HNTRACK_HITS(itrack,ihit)
            plane=HDC_PLANE_NUM(hit)
            if (plane.ge.7) then

* condition of above met calculating residuals  
* assigning rays to tracks in each chamber
* ray1 is ray from first chamber fit
* ray2 is ray from second chamber fit

            ray1(1)=dble(HX_FP(1))
            ray1(2)=dble(HY_FP(1))
            ray1(3)=dble(HXP_FP(1))
            ray1(4)=dble(HYP_FP(1))
            ray2(1)=dble(HX_FP(2))
            ray2(2)=dble(HY_FP(2))
            ray2(3)=dble(HXP_FP(2))
            ray2(4)=dble(HYP_FP(2))

            itrack=1
* loop over hits in second chamber
            do ihit=1,HNTRACK_HITS(itrack+1,1)

* calculate residual in second chamber from first chamber track
              hit=HNTRACK_HITS(itrack+1,ihit+1)
              plane=HDC_PLANE_NUM(hit)
              pos=H_DPSIFUN(ray1,plane)
              hdc_residual(itrack,plane)=HDC_WIRE_COORD(hit)-pos

            enddo

            itrack=2
* loop over hits in first chamber
            do ihit=1,HNTRACK_HITS(itrack-1,1)

* calculate residual in first chamber form second chamber track
              hit=HNTRACK_HITS(itrack-1,ihit+1)
              plane=HDC_PLANE_NUM(hit)
              pos=H_DPSIFUN(ray2,plane)
              hdc_residual(itrack,plane)=HDC_WIRE_COORD(hit)-pos

            enddo
            endif
          endif
        endif
      endif

*     test if we want to dump out trackfit results
      if(hdebugtrackprint.ne.0) then
         call h_print_tracks
      endif                                   ! end test on zero tracks
1000  return
      end

*