Keywords: imager

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#### Stability criterion

The simplest way to control the convergence is the blue`CLEAN_STOP` character variable. It allows to express the stopping threshold in natural units, e.g. Jy, mJy, K, milliK, Noise or Sigma (the noise levels), or even % for peak percentage.

But Clean convergence can also be controlled by the usual blue`CLEAN_ARES` (#1, maximum Absolute RESidual value) , blue`CLEAN_FRES` (#2, maximum Fractional RESidual value) and blue`CLEAN_NITER` (#3, maximum Number of ITERations) criteria, plus blue`CLEAN_NCYCLE` for methods with major cycles. A fourth criterium (#4) is convergence, which is controlled by blue`CLEAN_NKEEP`, a number of components. Deconvolution of a given channel stops if the cumulative flux at iteration number N is smaller (resp. larger) than at iteration N-`CLEAN_NKEEP` for positive signals (resp. negative). In essence, blue`CLEAN_NKEEP` is the number of components when the signal is just above the noise. Experimentation with various types of images has shown that blue`CLEAN_NKEEP=70` is a good compromise.

However, criteria #1-3 can be set to 0, allowing [rgb]1,0,0IMAGER to automatically guess when to stop. In this case, [rgb]1,0,0IMAGER uses an absolute residual threshold equals to the noise level (available in blue`dirty%gil%noise`), and estimates a (very conservative) maximum number of Clean components.

Using blue`CLEAN_STOP` has precedence over the other ways of specifying the stopping criteria.

Next: Formation of the CLEAN Up: CLEAN ideas Previous: Stopping criteria Contents Index