Keywords: map

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### Implementation

In MAPPING, the variants of the `CLEAN` algorithms discussed above are coded as the following commands: `HOGBOM`, `CLARK`, `MX`, `SDI`, `MULTI` and `MRC`. All those commands work on two internal buffers containing the dirty beam and dirty image. Both buffers are created directly from table through the `UV_MAP` command, or they can be loaded from files through the `READ BEAM` and `READ DIRTY` commands. The behavior of those commands is controlled through the following common sic variables:

Iterative search
  `POSITIVE`
    Number of positive clean components to be found before enabling the search for negative components. Default is 0.
  `GAIN`
    Loop gain. Default is 0.2, good compromise between stability and speed.
Stopping criteria
  `NITER`
    Maximum number of clean components. Default is 500.
  `FRES`
    Maximum amplitude of the absolute value of the residual image. This maximum is expressed as a fraction of the peak intensity of the dirty image. Default is 0.
  `ARES`
    Maximum amplitude of the absolute value of the residual image. This maximum is expressed in the image units (Jy/Beam). Default is 0.
Support
  `BLC` and `TRC`
    Bottom Left Corner and Top Right Corner of a square support in pixel units. Default is 0, meaning do not use such a square support.
  `SUPPORT`
    A command to interactively define the support where to search for clean components. This definition can be stored in a file through the `WRITE SUPPORT` command and read back in memory from the file with the `SUPPORT` command. The support definition is stored in the `POLY` sic structure. A side effect is that any definition of a polygon (e.g. through the `GO FLUX` command) will imply the definition of a support...
Clean beam parameters
  `MAJOR, MINOR` and `ANGLE`
    FWHM size of the major and minor axes (in arcsec) and position angle (in degree) of the Gaussian used to restore the clean image from the clean component list. Default is all parameters at 0, meaning use the fit of the main lobe of the dirty image. Changing the default value of those parameter is dangerous.

Other variables control specific aspects of a subclass of the `CLEAN` algorithms:

`NMAJOR`
  Maximum number of major cycles in all algorithms using this notion (`CLARK`, `MX`, `SDI`). Default is 50.
`BEAM_PATCH`
  Size (in pixel units) of the dirty beam used to deconvolve the residual image in minor cycles. It is used in all algorithms using the minor cycle notion. Default is 0, meaning *** ? JP ***
`SMOOTH`
  *** ? JP ***

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