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The Design

We introduce the following classes to model the measurement equation:

SkyEquation and VisEquation

are responsible for evaluating this equation, $\chi^{2}_{}$, and the gradients of $\chi^{2}_{}$.

VisSet

is responsible for providing coherence data to the SkyEquation and VisEquation and storing the results of predictions. It is thus simply a convenient interface to a Measurement Set. Iteration through the VisSet is accomplished by Iterators VisIter and ROVisIter.

SkyModel

supplies a set of images such as $\vec{I}\,$ to the SkyEquation.

SkyJones

supplies sky-plane-based calibration effects to the SkyEquation by multiplying a given image by matrices such as $\sf J^{sky}$. Indexing is via a VisIter object and image coordinates.

VisJones

supplies visibility-plane-based calibration effects to the VisEquation via either 2 by 2 or 4 by 4 matrices such as $\sf J^{vis}$. Indexing is via a VisIter object.

MJones

supplies interferometer-based gain effects to the VisEquation via a 4 by 4 matrix $\sf M$. Indexing is via a VisIter object.

ACoh

supplies interferometer-based offsets via a 4 vector $\vec{A}\,$. Indexing is via a VisIter object.

XCorr

applies a non-linear correlator function via a function X to a 4 vector. Indexing is via a VisIter object.

FTCoh

performs the Fourier transform. It is initialized and then coherences are fetched one by one from it, indexed via a VisIter object.

IFTCoh

performs the inverse Fourier transform. It is initialized and then fed coherences one by one. Finally an image is constructed.

WTCoh

performs reweighting. It is initialized and then weight are fetched one by one from it, indexed via a VisIter object.

All the objects SkyModel, SkyJones, VisJones, MJones, ACoh, and XCorr can potentially solve for themselves given a specific SkyEquation or VisEquation and VisSet. To do this, gradient information is accumulated into each object and then a method solve is used to estimate or update the object. For convenience, we actually provide an overloaded method solve for SkyEquation or VisEquation that simply calls the appropriate solve.