program r3dv
!$$$  main program documentation block
!                .      .    .                                       .
! main program: R3DVAR      onal 3-d variational analysis
!   PRGMMR: ROGERS           ORG: NP22        DATE: 98-01-05  
!
! abstract: the regional 3-d variational analysis routine
!   performs a regional analysis adapted to the eta model.  this
!   version of the analysis is done on pressure coordinates.  The 
!   horizontal analysis grid is every other row of the eta h-grid.
!   The analysis increments are interpolated in the horizontal
!   as necessary to get to the staggered points left out of the analysis
!   grid.  Then vertical interpolation to the eta coordinate is done
!   before the increment is added to the eta guess.
!   
!   The background error covariance is defined here not spectrally as
!   in the SSI, but using a recursive filter (J. Purser).  The form
!   used here is fast and flexible, allowing for
!   spatially varying error variance and correlation length.  There is
!   a small amount of distortion near the boundaries, which may not
!   matter very much, since correlation models are gross approximations
!   anyway.  However, there is allowance for a buffer zone around the
!   analysis domain, should this be a problem.
!
!   Because this analysis was initially created to assimilate doppler
!   radar winds, all winds are treated as line-of-sight winds.  A
!   conventional wind observation becomes two line-of-sight observations,
!   one along a north pointing line (earth v component) and one along
!   an east pointing line (earth u component).  All line-of-sight
!   winds, radar or conventional, are then assigned the angle that
!   each observation line-of-sight makes with the eta grid x-axis.
!   the forward model (which computes a simulated observation from 
!   model variables) is just
!           wobs(theta) = u*cos(theta) + v*sin(theta)
!   
! program history log:
!   95-01-24  parrish
!   95-02-03  parrish:  add wind analysis capability
!   95-02-15  parrish:  add ref level, sfc pressure data
!   95-02-16  parrish:  add stuff to update eta restart file
!   95-05-03  parrish:  begin conversion to observation space form
!                        using descent methods devised by J. Purser
!   95-08-04  parrish:  continue with rewrite, adding eta guess capability
!
!
! usage:
!   input files:
!	8 - snow.parm
!	9 - fix/eta3245_globstats
!	11 - fcstdata.parm
!	12 - nhb3245
!	13 - restart.ges
!	15 - fix/r3dvar.parm
!	16 - sges.3dvar
!	19 - fix/errtable.r3dv
!	22 - z0eff
!	30 - prepcq (bufr)
!	41 - hgtsmref
!	42 - snowdepth (grib)
!	43 - ice (grib)
!	44 - sst (grib)
!	45 - albedo (grib)
!	46 - veg (grib)
!   output files:
!	51 - restart
!	52 - nfc3245
! **************************
!    unit numbers are specified for most files on
!    input data cards. can be changed by changing data cards
! **************************
!     inprep   - input bufr data file from quality control routine
!     inges    - six hour forecast guess field
!
!   output files:  (including scratch files)
!     fort.6   - printout
!
!   subprograms called:
!     unique:    - subroutines: filterp filterx filtery 
!                -  fitoftemp fitoftemp2 fitofwind fitofwind2
!                -  gdcrdn gdcrdp getbufrdata
!                -  getgofp getguess gradpen
!                -  pcgr3dv r3dv r3dvex testfilter 
!                -  tfilterp tfilterx tfiltery tll
!                - 
!                - 
!
!                - function conmc
!     library:
!       w3lib    -
!
!   exit states:
!     cond =   0 - successful run
!          =  15 - no prepda data
!          =  56 - trouble in conmc
!
! remarks: resolution, unit numbers and several constants are
!          in the input data cards
!
! attributes:
!   language: fortran 9x (extensive use of dynamic memory feature)
!   machine:  cray
!
!$$$