; WEIGHTIT
;---------------------------------------------------------------
;! Controls modification of weights before gain/fringe solutions
;# ADVERB CALIBRATION UV VLBI
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;---------------------------------------------------------------
WEIGHTIT  LLLLLLLLLLLLUUUUUUUUUUUU CCCCCCCCCCCCCCCCCCCCCCCCCCCCC
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WEIGHTIT
Type: Adverb  (scalar)
Use:  A code controlling the modification of data weights prior to
      their use in gain solutions and fringe fitting.  Weighting by
      uncertainty squared may be too extreme a method, down-weighting
      outer antennas excessively and producing failed solutions.
      Weighting linearly by uncertainty may be more stable.
      Values:
          0 - no change   weighting by 1/sigma**2
          1 - sqrt (wt)   weighting by 1/sigma may be more stable
          2 - (wt)**0.25  weighting by 1/sqrt(sigma)
          3 - wt -> 1.0   no weighting
Null value:  0
Tasks:
   BPASS.....Computes spectral bandpass correction table
   BPWGT.....Calibrates data and scales weights by bandpass correction.
             WEIGHTIT selects the bandpass, its square root, or its
             fourth root.
   CALIB.....Determines antenna calibration: complex gain
   FLATN.....Re-grid multiple fields into one image incl sensitivity.
             WEIGHTIT is used to down-weight outer pixels in each
             facet.
   FRING.....Fringe fit data to determine antenna calibration, delay,
             rate.
   KRING.....Fringe fit data to determine antenna calibration, delay,
             rate.
   OMFIT.....Fits sources and, optionally, a self-cal model to uv data.
Procedures:
   IMFRING...Large image delay fitting with IM2CC and OOFRING.
   IMSCAL....Large image self-cal with IM2CC and OOCAL
   OOCAL.....Determines antenna complex gain with frequency-dependent
             models
   OOFRING...Fringe fit data to determine calibration with spectral
             index options.
   PEELR.....Calibrates interfering sources in multi-facet imges.
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