Keywords: imager

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## Data re-weighting

The data weights are not changed during the self-calibration solution search.

However, when applying the gain changes, the magenta`SELFCAL APPLY` command implementation makes a conscious choice the consequence of amplitude changes on the data weights. The weights are scaled down when the amplitude is increased (as thermal noise is also increased in proportion), but are untouched if the amplitude is decreased. In essence, [rgb]1,0,0IMAGER considers that self-calibration always degrades the noise.

Note that as a result of the different behaviour for the weights during the search and in the use of the solution, the last iterated image in the self-calibration search is not the image obtained after applying the solution. Even the angular resolution may change (hopefully only slightly).

This of course only applies for magenta`AMPLI` self calibration, since phase changes do not affect the noise.