[daip] forwarded message from Eric Greisen

[Eric Greisen]

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From: Eric Greisen <egreisen at nrao.edu>
To: Martin Hardcastle <mjh at star.herts.ac.uk>
Subject: Re: [daip] PCAL and models
Date: Fri, 16 Dec 2005 14:12:58 -0700

I have looked at the code in more detail.  I do not understand PCAL at
all and what fixes I have made have been to deal with general upgrade
issues that needed to be added to PCAL.  But, I checked the 1992
version that Bill claims to have been a working version.  It handles
the models with exactly the same code as the modern version.  Every
reference to XSMOD is identical and LPCALC seems unchanged too.

The subroutine PCLFLX computes a polarized model and puts it in the uv
scratch file with UVMSUB so that that file contains both the
visibilities and the model.  This uses the same trick that model
division does - sum the model in extra space in the "vis" file and
then read back to divide the actual vis by the model.  This seems to
give a polarizaed model every chance to work...  In fact, PCLFLX is
the routine that reads back this scratch file and prepares the two
arrays of VOBS and VMOD that are then used by LPCALC.  The latter then
only needs to know whether there is a model (VST(1,.) > 0) or not.

If it is not working , there is some problem, but that problem has
probably been there for 13 years or so.

Eric Greisen

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