Documentation on mfclean

Task: mfclean
Purpose: Multi-frequency synthesis CLEAN.
Categories: deconvolution

        MFCLEAN is a MIRIAD task to deconvolve a multi-frequency synthesis
        image. It can perform either Clark or Hogbom iterations.
        To achieve good results, the width of the beam should be at
        least 3 times that of the region being cleaned. The
        region being cleaned should be reasonably centred in the map, and
        should have an appreciable guard band around it to the map edge (of
        size comparable to the width of the region being cleaned).

        To form a multi-frequency synthesis image and beam, use INVERTs
        ``mfs'' and ``sdb'' options. This will create
        a map with one plane, and a beam with two planes (the normal dirty
        beam, and the spectral dirty beam).

        The result of MFCLEAN is a component image, consisting of two planes.
        The first plane is the normal flux components. The second plane are
        components of ``flux times spectral index'' (that is, I*alpha).

        Use task MFSPIN to get a crude spectral index image from the output
        of MFCLEAN.

        The sign convention used for the spectral index, alpha, is that:
          I(f) = I(f0) * (f/f0) ** alpha

        MFCLEAN differs from CLEAN in a number of ways.
        * Task CLEAN only requires that the beam is twice the size of the
          region being cleaned whereas, for MFCLEAN, it is recommended that
          the dirty beam be three times the size of the region being cleaned.
        * MFCLEAN requires a guard band around the edge of the region being
          cleaned.
        * MFCLEAN does not have a Steer cleaning option, nor prussian hats.

Key: map
        The input dirty map, which should have units of Jy/beam. No
        default. 

Key: beam
        The input dirty beam. This should be formed using INVERT with
        options=sdb. No default.

Key: model
        An initial model of the deconvolved image. This could be the
        output from a previous run of MFCLEAN. It must have flux units of
        Jy/pixel. The default is no model (i.e. a zero map).

Key: out
        The name of the output map. The units of the output will be
        Jy/pixel. This file will contain the contribution of the input model.
        It will consist of two planes, giving the flux density image and the
        "flux times spectral index" image (also called the scaled flux
        derivative image). No default.

Key: gain
        The minor iteration loop gain. Two values can be given, the second
        being the gain for the spectral components. If only one value is
        given, the flux and spectral components use the same gain. The
        default is 0.1.

Key: cutoff
        MFCLEAN finishes when the absolute maximum residual falls below
        CUTOFF. Default is 0. 

Key: niters
        The maximum number of minor iterations. MFCLEAN finishes when
        abs(NITERS) minor iterations have been performed. Clean may finish
        before this point, however, if NITERS is negative and the absolute
        maximum residual becomes negative valued, or if the cutoff level
        (as described above) is reached. 

Key: region
        This specifies the region to be Cleaned. See the Users Manual for
        instructions on how to specify this. The default is the inner
        quarter. This default is generally inadequate, and a smaller
        region should be explicitly specified.

Key: minpatch
        The minimum patch size when performing minor iterations. Default
        is 51, but make this larger if you are having problems with
        corrugations. You can make it smaller when cleaning images which
        consist of a pretty good dirty beam. 

Key: speed
        This is the same as the speed-up factor in the AIPS APCLN.
        Negative values makes the rule used to end a major iteration more
        conservative. This causes less components to be found during a
        major iteration, and so should improve the quality of the Clean
        algorithm. Usually this will not be needed unless you are having
        problems with corrugations. A positive value can be useful when
        cleaning simple point-like sources. Default is 0. 

Key: mode
        This can be either "hogbom", "clark" or "any", and
        determines the Clean algorithm used. If the mode is "any", then
        MFCLEAN determines which is the best algorithm to use. The default
        is "any".