Documentation on closure

Task: closure
Categories: uv analysis, plotting

        CLOSURE is a Miriad task which plots closure phase and triple
        product amplitude. The task works by averaging triple products
        (the product of three correlations around a closure triangle).
        These are always averaged over the selected frequency channels and
        over the parallel-hand polarizations. Optionally the triple
        correlation can also be averaged over time and over the different
        closure triangles.

        CLOSURE also prints (and optionally plots) the theoretical error
        (as a result of thermal noise) of the closure phase and triple
        amplitudes. Note this assumes a point source model, and that the
        signal-to-noise ratio is appreciable (at least 10) in each averaged
        triple product.

        Note: triple amplitude is the cubic root of the
        product of three correlations around a closure triangle. It is
        an estimate of the flux of a point source which is indepedent of
        closing errors.

Key: vis
        The input visibility datasets. Several datasets can be given.

Key: select
        Standard visibility selection. See help on select for more
        information.

Key: line
        Standard visibility linetype. See the help line for more information.

Key: stokes
        Normal Stokes/polaization selection. Correlations other than
        parallel-hand ones are ignored.

Key: device
        PGPLOT plotting device. The default is no plotting device (the
        program merely prints out some statistics).

Key: nxy
        The number of plots per page in x and y. The default depends on
        the number of plots.

Key: yrange
        The y range of the plots. The default is to autoscale.

Key: interval
        Time averaging interval. The default is no time averaging of the
        triple correlations.

Key: options
        Task enrichment parameters. Several parameters can be given, separated
        by commas. Minimum match is supported. Possible options are:
          avall     Average all triple correlations from different triangles
                    together. Note the theoretical error estimates are
                    incorrect when using options=avall.
          notriple  Plot data from all closure triangles on a single plot.
          amplitude Plot triple amplitude (the default is to plot closure
                    phase).
          rms       Plot theoretical error bars on the points. The error
                    bars are +/- sigma.
        The following give control over calibration to be applied to the
        visibility data before the triple correlations are formed. Note
        that applying phase calibrations does not affect the closure phase!
          nocal     Do not perform gain calibration.
          nopol     Do not perform polarisation calibration on the data.
          nopass    Do not perform bandpass calibration on the data.