[daip] weights, dividing by models

[Olaf Wucknitz]

Hi Eric,

I made some tests with UVSUB (OPCODE=DIV) to see what happens to the 
weights. When using the gridded-FFT method, I find that indeed the weights 
are scaled with amplitude**2.
However, if I use SMODEL or DFT computation of a CC model, the weights are 
instead scaled with the amplitude.

Do CALIB, FRING, BLCAL and others use the same routines to divide by a 
model? I find it a bit difficult to follow these parts of the source code 
with all the branches for different model types etc.

Cheers,
Olaf



> I suspect that the comments somewhere are not correct.  The weights are
> scaled by the square of the amplitudes at present - I suspect that the
> amplitude was used in the earliest of days.  Note that this weighting
> seems to cause model fits (e.g. CALIB) to fail when the model
> improves!  This is why such tasks have a DOWEIGHT parameter to take
> weights to some power (e.g. 1/2) so that weights do not differ by so
> much between short and long spacings.
> 
> Eric Greisen