AIPS NRAO AIPS HELP file for MAXPIXEL in 31DEC18



As of Wed Jan 17 6:09:57 2018



HELP SECTION

MAXPIXEL
Type:  Adverb (scalar)
Use:   Specifies the maximum number of pixels to be searched
       for Clean components during each major cycle of the Clark
       version of Clean.
Null Value: 0 => 20050.
Tasks:
   MX.......Make and deconvolve images from calibrated single-
            source UV data files.
   APCLN....Deconvolve images.
   SDCLN....Deconvolve images, switching to Steer-Dewdnet-Ito
            algorithm after a while.

Discussion:
   AIPS Clean algorithm was designed by Barry Clark and modified
   by Bill Cotton.  In it, a certain number of the highest
   pixels in the residual image is loaded to the "AP" memory to
   be searched for components during each major cycle.  The
   performance and the results of the clean depend a lot on how
   many pixels are searched.  If too few are searched, then each
   cycle will find only a few components and there will have to
   be many (expensive) major cycles.  If too many are searched,
   then the algorithm wastes a lot of time searching and
   subtracting from pixels it does not ever need.  Also, when a
   large number are searched, a larger beam patch is needed to
   avoid making too much error inside the cycle.  Use this
   option sparingly, but values like 25000 or 30000 are found to
   speed cleans of large images that develop many approximately
   equal pixels in the residual image.

EXPLAIN SECTION


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