AIPS NRAO AIPS HELP file for KRING in 31DEC19



As of Tue Dec 11 22:47:51 2018


KRING: Task to fringe-fit data

INPUTS

INNAME                             INPUT UV name      (required)
INCLASS                                     class
INSEQ                                       sequence #
INDISK                                      disk #
CALSOUR                            Select by source name ''=>all
QUAL                                         qualifier   -1=>all
CALCODE                                      calcode     ''=>all
SELBAND                            Bandwidth to select     (kHz)
SELFREQ                            Frequency to select     (MHz)
FREQID                             Freq. ID to select   < 1=>all
TIMERANG                           Time range to use      0=>all
BCHAN                              Lowest channel number  0=>all
ECHAN                              Highest channel number 0=>all
ANTENNAS                           Antennas to select     0=>all
DOFIT                              Antennas to solve for  0=>all
SUBARRAY                           Subarray               0=>all
UVRANGE                            Range of uv distance
                                   for full weight        0=>all
WTUV                               Weight outside UVRANGE 0=>0.0
WEIGHTIT          0.0        3.0   Modify data weights function
DOCALIB          -1.0      101.0   > 0 calibrate data & weights
                                   > 99 do NOT calibrate weights
GAINUSE                            CL table #
DOPOL            -1.0       10.0   If >0 correct polarization.
PDVER                              PD table to apply (DOPOL>0)
BLVER                              BL table to apply.
FLAGVER                            FG table #
DOBAND                             >0 apply BP table
                                                 See HELP DOBAND
BPVER                              BP table #
SMOOTH                             Spectral smoothing function
                                                 See HELP SMOOTH
IN2NAME                            CLEAN map name     (optional)
IN2CLASS                                     class
IN2SEQ                                       sequence #
IN2DISK                                      disk #
INVERS                                       CC table #
NCOMP                                        # CC's/field to use
FLUX                                         CC flux cutoff
NMAPS                                        # Clean map files
CMETHOD                                      Modeling method:
                                             'DFT','GRID',' '
CMODEL                             Model type: 'COMP','IMAG'
                                   'SUBI' (see HELP re images)
SMODEL                             Source model, 1=flux,2=x,3=y
                                                 See HELP SMODEL
REFANT                             Reference antenna
SEARCH                             Fringe search list.
SOLINT                             Soln. interval (min)    0=>10
SOLSUB                             Solution subinterval
SOLMIN                             Min solution interval
SOLTYPE                            'NOLS' => do FFT only
                                   'NOFT' => do LS only
                                   other => do FFT + LS
SOLMODE                            NRD = indep. rates/delays
                                   NR  = indep. rates, no delays
                                   ND  = indep. delays, no rates
                                   R   = one rate, no delays
                                   RD  = one rate/mb-delay
                                   RDS = one rate,mb-/sb-delays
                                   RI  = one rate/iono-delay
                                   TD  = mb-delay + dispersion
                                   default = NRD, see HELP
DOIFS              0.0      64.0   1 => 1 solution for all IFs
                                   2 => 2 solutions, 1 each for
                                        IFs by halves
                                   N => N solutions, 1 each for
                                        NIF/N IFs
                                   0 -> 1  (use 1 for T, S)
                                   SOLMODE must include N to do
                                   each IF individually (DOIFS
                                   is ignored)
OPCODE                             'ZRAT' => zero rates
                                        for more, See HELP KRING
CPARM                              1 min T_int(sec) 0 => 2
                                   2 delay win(ns)  0 => Nyquist
                                   3 rate win(mH)   0 => Nyquist
                                   4 SNR cutoff     0 => 3
                                                  -1 => pass all
                                   5 FFT baseline stacking?
                                                    0 => yes
                                                    1 => no
                                   6 search to which antennas?
                                                    0 => all
                                     1 => only those on SEARCH
                                               list
                                   7 >0 average RR and LL
                                   8 <=0 rereference solutions
                                   9 max SOLINT (min) 0=>10
                                   10 >0 try extrapolation and
                                              reverse traverse
                                     [possibly broken, see HELP]
SNVER                              Output SN table, 0=>new table
ANTWT                              Ant. weights (0=>1.0)

BIF                                First IF included when
                                   when SOLMODE has no N
EIF                                Last IF included when
                                   when SOLMODE has no N
PRTLEV                             Print level: 0-> count solns
                                   1-> LS info  2-> FFT info
BADDISK                            Disk # to avoid for scratch
                                                       files.

HELP SECTION

KRING
Task:  This task determines phase, rate, and delay corrections
       to be applied to a uv data set given a model of the source(s).
       The corrections are written to an SN table attached to the
       input Multi-Source UV data set.
   *** The delay/rate searchs are automatically turned off if less than
       two points are available along the corresponding freq/time axes.
   *** Plus signs next to the SNR during the FFT stage indicate the
       level of baseline stacking used to attain the reported SNR.
       SNRs for baselines with differing amounts of stacking should
       not be compared!
   *** The LS and FFT SNRs now agree with each other for unstacked
       data processed one baseline at a time [ostensibly to < 1 percent].
  QUESTIONS, COMMENTS?  [write to daip@nrao.edu]
	[Last documentation overhaul = 20 Oct 1999
       [coming one day? - probability of false detection, multiple SN
        tables, BL tables...]
Adverbs:
  INNAME.....Input UV file name (name).    Standard defaults.
  INCLASS....Input UV file name (class).   Standard defaults.
  INSEQ......Input UV file name (seq. #).  0 -> highest.
  INDISK.....Disk drive # of input UV file.  0 -> any.
  CALSOUR....List of sources for which calibration constants are to be
             determined, i.e. the calibrator sources  All ' ' = all
             sources; a "-" before a source name. means all except ANY
             source named.  Note: solutions for multiple sources can
             only be made if the sources are point sources at their
             assumed phase center and with the flux densities given in
             the source (SU) table.
  QUAL.......Only sources with a source qualifier number in the SU table
             matching QUAL will be used if QUAL is not -1.
  CALCODE....Calibrators may be selected on the basis of the calibrator
             code:
                  '    ' => any calibrator code selected
                  '*   ' => any non blank code (cal. only)
                  '-CAL' => blank codes only (no calibrators)
                  anything else = calibrator code to select.
             NB: The CALCODE test is applied in addition to the other
             tests, i.e. CALSOUR and QUAL, in the selection of sources
             for which to determine solutions.
  SELBAND....Bandwidth of data to be selected. If more than one IF is
             present SELBAND is the width of the first IF required.
             Units = kHz, 0=> all
  SELFREQ....Frequency of data to be selected. If more than one IF is
             present SELFREQ is the frequency of the first IF required.
             Units = MHz, 0=> all
  FREQID.....Frequency identifier to select (you may determine which is
             applicable from the OPTYPE='SCAN' listing produced by
             LISTR.  If either SELBAND or SELFREQ are set their values
             override that of FREQID, however setting SELBAND and
             SELFREQ may result in an ambiguity, in which case the task
             will request that you use FREQID.
  TIMERANG...Time range of the data to be used. In order: Start day,
             hour, min. sec, end day, hour, min. sec. Days relative to
             reference date.
  BCHAN......First channel to use.   0=>first available.
  ECHAN......Highest channel to use. 0=>highest available.
  ANTENNAS...A list of the antennas to have solutions determined. If
             any number is negative then all antennas listed are NOT to
             be used to determine solutions and all others are. 0 =>
             0 => use all.
  DOFIT......A list of the antennas for which solutions should or
             should not be determined.  If DOFIT = 0, all antennas are
             solved for.  If any entry <= -1, , then DOFIT is taken as
             the list of antennas for which no solution is desired; a
             solution is found for all antennas not in DOFIT.  If any
             entry of DOFIT is non-zero and all are >= 0, then only
             those antennas listed in DOFIT will be solved for - all
             other selected antennas will not be solved for.
             NOTE: THIS OPTION MUST NOT BE USED UNLESS YOU UNDERSTAND
             IT FULLY.  Basically, it should be used to solve for the
             gains of "poor" antennas after the "good" antennas have
             been fully calibrated.  Antennas included in ANTENNAS but
             not in DOFIT are assumed to have a complex
             gain/delay/rate of (1,0,0,0) and the gains/delays
             produced will be very wrong if this is not the case.
             See HELP DOFIT.
  SUBARRAY...Subarray number to use. 0=>all.
  UVRANGE....The range of uv distance from the origin in kilowavelengths
             over which the data will have full weight; outside of this
             annulus in the uv plane the data will be down weighted by a
             factor of WTUV.
  WTUV.......The weighting factor for data outside of the uv range
             defined by UVRANGE.
  WEIGHTIT...If > 0, change the data weights by a function of the
             weights just before doing the solution.  Choices are:
             0 - no change   weighting by 1/sigma**2
             1 - sqrt (wt)   weighting by 1/sigma may be more stable
             2 - (wt)**0.25
             3 - change all weights to 1.0
  DOCALIB....If true (>0), calibrate the data using information in the
             specified Cal (CL) table for multi-source or SN table for
             single-source data.  Also calibrate the weights unless
             DOCALIB > 99 (use this for old non-physical weights).
  GAINUSE....version number of the CL table to apply to the data.
             0 => highest.
  DOPOL......If > 0 then correct data for instrumental polarization as
             represented in the AN or PD table.  This correction is
             only useful if PCAL has been run or feed polarization
             parameters have been otherwise obtained.  See HELP DOPOL
             for available correction modes: 1 is normal, 2 and 3 are
             for VLBI.  1-3 use a PD table if available; 6, 7, 8 are
             the same but use the AN (continuum solution) even if a PD
             table is present.
  PDVER......PD table to apply if PCAL was run with SPECTRAL true and
             0 < DOPOL < 6.  <= 0 => highest.
  BLVER......Version number of the baseline based calibration
             (BL) table to appply. <0 => apply no BL table,
             0 => highest.
  FLAGVER....Specifies the version of the flagging table to be applied.
             0  => highest numbered table.
             <0 => no flagging to be applied.
  DOBAND.....If true (>0) then correct the data for the
             shape of the antenna bandpasses using the BP table
             specified by BPVER. The correction has three modes:
             (a) if DOBAND=1, all entries for an antenna in the table
             are averaged together before correcting the data.
             (b) if DOBAND=2, the entry nearest in time is used to
             correct the data.
             (c) if DOBAND=3, the table entries are interpolated in time
             and the data are then corrected.
  BPVER......(multi-source) version of the BP table to be applied.
             0 => highest; < 0 => no bandpass correction to be applied.
  SMOOTH.....Specifies the type of spectral smoothing to be applied to
             a uv database . The default is not to apply any smoothing.
             The elements of SMOOTH are as follows:
             SMOOTH(1) = type of smoothing to apply: 0 => no smoothing
               To smooth before applying bandpass calibration
                 1 => Hanning, 2 => Gaussian, 3 => Boxcar, 4 => Sinc
               To smooth after applying bandpass calibration
                 5 => Hanning, 6 => Gaussian, 7 => Boxcar, 8 => Sinc
             SMOOTH(2) = the "diameter" of the function, i.e. width
               between first nulls of Hanning triangle and sinc
               function, FWHM of Gaussian, width of Boxcar. Defaults
               (if < 0.1) are 4, 2, 2 and 3 channels for SMOOTH(1) =
               1 - 4 and 5 - 8, resp.
             SMOOTH(3) = the diameter over which the convolving
               function has value - in channels.  Defaults: 1,3,1,4
               times SMOOTH(2) used when input SMOOTH(3) < net
               SMOOTH(2).

The following specify a CLEAN model to be used if a single source via
specified in CALSOUR:
  IN2NAME....Cleaned map name (name).      Standard defaults.
             Note: a CLEAN image for only a single-source may
             be given although it may be in a multi-source file.
             If the source table contains a flux, then that flux will
             be used to scale the components model to obtain the
             stated total flux.  This is needed since initial Cleans
             may not obtain the full flux even though they represent
             all the essentials of the source structure.
  IN2CLASS...Cleaned map name (class).     Standard defaults.
  IN2SEQ.....Cleaned map name (seq. #).    0 -> highest.
  IN2DISK....Disk drive # of cleaned map.  0 => any.
  INVERS.....CC file version #.  0=> highest numbered version
  NCOMP......Number of Clean components to use for the model, one
             value per field.  If all values are zero, then all
             components in all fields are used.  If any value is not
             zero, then abs(NCOMP(i)) (or fewer depending on FLUX and
             negativity) components are used for field i, even if
             NCOMP(i) is zero.  If any of the NCOMP is less than 0,
             then components are only used in each field i up to
             abs(NCOMP(i)), FLUX, or the first negative whichever
             comes first.  If abs(NCOMP(i)) is greater than the number
             of components in field i, the actual number is used.  For
             example
                   NCOMP = -1,0
             says to use one component from field one unless it is
             negative or < FLUX and no components from any other
             field.  This would usually not be desirable.
                   NCOMP = -1000000
             says to use all components from each field up to the
             first negative in that field.
                   NCOMP = -200 100 23 0 300 5
             says to use no more than 200 components from field 1, 100
             from field 2, 23 from field 3, 300 from field 5, 5 from
             field 6 and none from any other field.  Fewer are used if
             a negative is encountered or the components go below
             FLUX.
  FLUX.......Only components > FLUX in absolute value are used in the
             model.
  NMAPS......Number of image files to use for model.  For multi-scale
             models, set NMAPS = NFIELD * NGAUSS to include the Clean
             components of the extended resolutions.  If more than one
             file is to be used, the NAME, CLASS, DISK and SEQ of the
             subsequent image files will be the same as the first file
             except that the LAST 3 or 4 characters of the CLASS will
             be an increasing sequence above that in IN2CLASS.  Thus,
             if INCLASS='ICL005', classes 'ICL005' through 'ICLnnn'
             or 'ICnnnn', where nnn = 5 + NMAPS - 1 will be used.  Old
             names (in which the 4'th character is not a number) are
             also supported: the last two characters are '01' through
             'E7' for fields 2 through 512.  In old names, the highest
             field number allowed is 512; in new names it is 4096.
  CMETHOD....This determines the method used to compute the model
             visibility values.
             'DFT' uses the direct Fourier transform, this method is
                   the most accurate.
             'GRID' does a gridded-FFT interpolation model computation
             '    ' allows the program to use the fastest method
  CMODEL.....This indicates the type of input model; 'COMP' means that
             the input model consists of Clean components, 'IMAG'
             indicates that the input model consists of images.
             'SUBI' means that the model consists of a sub-image of
             the original IMAGR output.  If CMODEL is '   ' Clean
             components will be used if present and the image if not.
             SUBI should work for sub-images made with DO3DIM true and
             sib-images of the central facet made with DO3DIM false,
             but probably will not work well for shifted facets with
             DO3DIM false.  Use BLANK rather than SUBIM in such cases.
             CALIB will set a scaling factor to correct image units
             from JY/BEAM to JY/PIXEL for image models.  If the source
             table contains a flux, then that flux will be used to
             scale the components model to obtain the stated total
             flux.  This is needed since initial Cleans may not obtain
             the full flux even though they represent all the
             essentials of the source structure.
  SMODEL.....A single component model to be used instead of a CLEAN
             components model; if abs (SMODEL) > 0 then use of this
             model is requested.
                SMODEL(1) = flux density (Jy)
                SMODEL(2) = X offset in sky (arcsec)
                SMODEL(3) = Y offset in sky (arcsec)
                SMODEL(4) = Model type:
                  0 => point model
                  1 => elliptical Gaussian and
                       SMODEL(5) = major axis size (arcsec)
                       SMODEL(6) = minor axis size (arcsec)
                       SMODEL(7) = P. A. of major axis (degrees)
                  2 => uniform sphere and
                       SMODEL(5) = radius (arcsec)
The following control how the solutions are done, if you don't
understand what a parameter means leave it 0 and you will probably get
what you want.
  REFANT.....The desired reference antenna for phases.  Note that
             the desired refant is not required to be the primary search
             antenna.  You should choose the REFANT to be an antenna
             that is present during most of the observation.
  SEARCH.....List of prioritized reference antennas to be used for
             fringe searching during the FFT stage.  KRING constructs
             an internal search list to determine the order in which to
             perform the FFTs.  This search list is constructed by first
             copying the elements of SEARCH.  Finally, all remaining
             antennas antennas are appended to the search list in
             numerical order.  You can limit the search to only the
             specified elements of the SEARCH list by setting CPARM(6).
             Only baselines where at least one antenna appears in the
             search list will be searched for fringes.
             You should explicitly order the antennas in terms of decreasing
             sensitivity if at all possible.
  SOLINT.....The solution interval.  Note that this is only a
             recommended solution interval.  The actual solution interval
             used by KRING will be changed in order to divide each scan
             evenly into an integral number of data chunks.
             SOLINT is in minutes; the default value (SOLINT=0) is 10
             minutes.  SOLINT values larger than 10 are reset to 10 minutes
             unless CPARM(9)>0.  NB: If SOLINT > 0.75*Scan, SOLINT = Scan.
  SOLSUB.....The begin time for the next interval in advanced from the
             current one by SOLINT / SOLSUB where 1 <= SOLSUB <= 10.
             0 -> 1.  This is to produce solutions at sub-intervals of
             SOLINT based on SOLINT length of averaging.
  SOLMIN.....Minimum number of subintervals to be used in a solution.
             0 -> SOLSUB.
  SOLTYPE....If 'NOLS', only a FFT delay/rate search is performed.
             If 'NOFT', only a LS delay/rate search is performed.
             Otherwise, a FFT search is followed by a Least Squares search.
  SOLMODE....This four character string controls the types of parameters
             to be solved for.  In any order, the following may be
             specified:
              N -> solve for N sets of quantities [ per IF ]
                   *** see DOIFS for solutions spanning > 1 IF.***
              R -> solve for rate [ per IF or
                                    only one common to all IFs ]
              D -> solve for delay [ per IF (single band delays) or
                                     only one (multi-band delay) ]
              S -> solve for stair-step delay [ only one, usually only
                                                needed for MkIII data
                                                where pulse-cals have
                                                been used ]
              I -> solve for an ionospheric delay [ only one, approx.
                                                    proportional to
                                                    inverse frequency ]
              T -> solve for an ionospheric delay [ only one, exactly
                                                    proportional to
                                                    inverse frequency ]
              4,2, or 1 -> use a factor of 4,2, or 1 of zero padding in the
                               FFTs.[use 4,2, or 1 for speed over accuracy]
             *** If N is specified, I,S,T are ignored.
                 [T also stores the ionosphere in the mb-delay column
                    so you can see the solved for values using SNPLT.
                  The actual phase/delay solutions stored using I or T
                    are identical.]
             *** Phases are always solved for***
             Commonly encountered modes would be:
             NRD = APARM(5)=0 in FRING
             RD  = APARM(5)=1 in FRING
             RDS = APARM(5)=2 in FRING
             ND, D, DS = same as NRD, RD, and RDS respectively but
                         do not solve for rates
             NR, R     = same as NRD and RD, respectively but
                         do not solve for any type of delays
             Default is NRD .
             *** Note Bene,  SOLMOD = 'ND' is different from
                      SOLMOD = 'NRD', OPCODE='ZRAT' .  The latter
                      first determines the best fitting rate along
                      with other solutions and then zeroes the rate
                      solution in the final SN table - this is usually
                      what you want.
  DOIFS......If DOIFS is set to N, then determine N solutions using
             NIF/N IFs in each one.  Note that NIF must be an integer
             multiple of N or the task will quit.  The default is 1
             but will be set to 0 (separate solutions for each IF if
             SOLMODE contains an 'N').
  OPCODE.....Solution masking to be performed _after_ fringe-fitting
             ' '  no masking
             'ZPHS'  zero phases in output SN table
             'ZRAT'  zero rates in output SN table
             'ZDEL'  zero delays in output SN table
             If CPARM(8)>0, OPCODE is forced = ' '.
  CPARM(1)...The minimum integration time of the data (sec);
             0 => 2 'VLBA' seconds
               It is important to get this number right to within 20  percent.
               E.g., if you've averaged up 1 second data to 10 seconds,
               setting this to 10 is okay so long as there are only a
               very few points with shorter than 10 second integration
               times.  If you set this to 1 second, you will regret it.
  CPARM(2)...The delay window FW to search (nsec) centered on 0 delay.
             <= 0 => full Nyquist range.
             [Use SOLMOD to turn off the delay search.]
  CPARM(3)...The rate window FW to search (mHz) centered on 0 rate.
             <= 0 => full Nyquist range.
             [Use SOLMOD to turn off the rate search.]
  CPARM(4)...The minimum allowed signal-to-noise ratio.  <0 => 3
             The SNR calculation is described in AIPS Memo 101.
             [You might consider setting this to 5.]
  CPARM(5)...Number of baseline combinations to use in the initial,
             FFT fringe-search (1-3).  Larger values increase the
             point source sensitivity but reduce the sensitivity to
             extended sources when an accurate model is not available.
             0=>3.
             [Solutions formed using combinations of baselines are
              marked with a plus for singly indirect combinations and
              with two pluses for doubly indirect combinations.]
  CPARM(6)...If CPARM(6)=1, only baselines to those antennas on the
             SEARCH list are searched during the FFT stage.  Otherwise,
             other baselines are eventually searched until either fringes
             have been found to each antenna, or no baselines remain to
             be searched.
  CPARM(7)...If >0, RR and LL data are averaged together and only a
             single solution is determined for both polarizations.  This
             is useful when reducing polarization data.
  CPARM(8)...If <= 0 then the phase, rate and delays will be
             re-referenced to a common antenna.  CPARM(8)=1 is only
             desirable for VLBI polarization data. Using this option also
             forces OPCODE = ' '.
  CPARM(9)...If SOLINT>10 is desired, you must set CPARM(9)>0 .  This
             is necessary to prevent accidentally requesting more memory
             than your computer can deliver and locking up computer.
  CPARM(10)..Try Hard Option.  If CPARM(10)>=0, When KRING is ready to
             do the initial FFT-based fringe search, it will first try
             to initialize residual fringe-fit delay and rate solns for
             each antenna using an average of all good solutions found
             in the SN table.  Only those antennas for which acceptable
             solutions are not found will then be FFTd to find fringes.
             This does not preclude the final Least Squares refinement.
             [20 Oct 1999, it has been reported that CPARM(10) is broken -
              it may trash the solutions - dont try it unless you have
              the time to re-run KRING if need-be.]
  SNVER......Desired output SN table.  Solutions will be added to the
             specified table replacing any previous solutions for the
             same TIMERANG, CALSOUR etc. 0 means create a new SN table.
  ANTWT......Antenna weights.  These are additional weights to be
             applied to the data before doing the solutions, one per
             antenna.  Use PRTAN to determine which antenna numbers
             correspond to which antennas.  This really is unnecessary
             in most cases now.
  BIF........First IF included when when SOLMODE does not contain an
             N (all IFs receive the solution found for the appropriate
             group of IFs, but only BIF-EIF are used to find it).
  EIF........Last IF included when when SOLMODE does not contain an
             N (all IFs receive the solution found for the appropriate
             group of IFs, but only BIF-EIF are used to find it).
  PRTLEV.....Print flag,
             0=minimal - (almost nothing).
             1 = LS solution information + scan information
             2 = FFT solution information
             3 = nothing really new.
             >3, all kinds of debugging info.
  BADDISK....A list of disk numbers to be avoided when creating scratch
             files.

EXPLAIN SECTION

KRING - who wrote it? ?  who rewrote it? kdesai@nrao.edu
KRING - documentation? - kdesai@nrao.edu [with input from mrupen@nrao.edu]
KRING - currently maintained by? - kdesai@nrao.edu
need help? - daip@nrao.edu

For some basic introduction to fringe-fitting, please see the discussions
in:

Chapter 9 of Interferometry and Synthesis in Radio Astronomy,
AR Thompson, JM Moran, & GW Swenson Jr., Krieger Publishing, 1991

Global Fringe Search Techniques for VLBI,
FR Schwab, WD Cotton, AJ, 88, 5, 1983

The Calculation of SNR in KRING's FFT stage,
KM Desai, AIPS MEMO 101, 1998

The AIPS cookbook also describes how and when KRING should be used.

Brief description:
KRING is a rewrite of the AIPS fringe-fitting task FRING.
BLING/BLAPP is an alternate method of fringe-fitting in AIPS.

These tasks all implement in one way or another the global fringe-
fitting algorithm described in Schwab and Cotton.

KRING differences from FRING:

MEMORY USAGE:
-KRING uses up to a third less memory for full Nyquist window
 searches and can save even more if smaller search windows are
 specified.

-KRING uses an indexing scheme to track the integration times on
 different baselines.  This scheme has its weaknesses [it does not
 gracefully handle the case when the integration times are not all
 multiples of the shortest integration time] but in most data sets
 now produced by the VLBA correlator, uses (N-2)*(N-1)* T_int_max /
 (2 * T_int_min) less memory [N is the number of stations in the
 data set].

SCRATCH FILE USAGE:
-FRING creates a scratch file consisting of calibrated _uncompressed_
 data.  If a complicated source model is used, this scratch file is
 potentially _SIX_ times bigger than the original [compressed] data
 set.

 KRING requires an NX table and creates scratch files for one scan at
 a time.  This results in much smaller scratch file usage at the cost
 of some overhead to create each scratch files.  This is a noticeable
 penalty when fringe-fitting phase-referenced observations.
 Currently, the scratch file grows as longer scans are found
 but does not shrink when shorter scans are encountered.

SOLUTION INTERVALS:
 KRING uses a different scan-breaking algorithm to try to make all
 solutions in a scan the same length - this algorithm may be more
 robust than FRING when: the user asks for one solution per scan, the
 TIMERANG is set.

RESTRICTED DELAY/RATE SEARCHES
 KRING implements delay and rate searching more uniformly so that the
 options to turn off delay or rate searches now work- previously it was
 difficult to turn off the rate search.

SOLUTION EXTRAPOLATION and REVERSE TRAVERSE
 KRING can try to extrapolate solutions from previously found
 solutions.  Before doing an FFT, KRING will check if the average of
 all previously found solutions has an SNR larger than the cutoff.
 If so, the delay and rate are adopted and a new phase solution is
 computed.  If the average solution's SNR is too low, KRING
 falls back to doing the FFT.  This can be expensive for data of
 uniformly poor quality of with uniformly weak fringes and should be
 turned not be used in such cases.  This option is off by default.
 [20 Oct 99, it has been reported that CPARM(10) is broken, I don't
  recommend its use until further notice. Sorry for the
  inconvenience!]

SNR CALCULATIONS:
 The SNR calculation in KRING is based upon an analytical expression
 for the SNR that can be found in AIPS memo 101.  Note that the SNR
 calculations from the LS and FT stages are only expected to agree
 when processing one baseline at a time [but, in that case, they are
 expected to agree to within 1 percent].







AIPS