[daip] [Fwd: visibility weight problem in output of DIFUV]
Huib Intema
hintema at nrao.edu
Thu Nov 12 10:16:49 EST 2009
Is there any news on this matter?
Regards,
Huib
-------- Original Message --------
Subject: visibility weight problem in output of DIFUV
Date: Thu, 05 Nov 2009 14:03:27 -0500
From: Huib Intema <hintema at nrao.edu>
Organization: National Radio Astronomy Observatory
To: daip at nrao.edu
Dear DAIP,
I use DIFUV to subtract a model UV database from a real UV database. The
model UV database is created with UVSUB with OPCODE = 'MODL', using the
real UV database as input, which results in model visibilities having
the same weights as in the input. Before (using a mid-2008 copy of
AIPS), I needed to run WTMOD on the output of DIFUV with APARM(1)=0.5 to
compensate for the unwanted summation of (quadratic?) weights by DIFUV.
I found that DIFUV in the current 2009 AIPS causes the output visibility
(quadratic?) weights to be halved rather than doubled. This I could fix
by using WTMOD with APARM(1)=2.0. However, when the input visibility
weights are both zero the output weight is NaN. This looks like a zero
division error while adding the reciprokes of the input visibility
weights rather than the weights themselves.
Regards,
Huib
(running the binary MNJ AIPS on a 64-bit Linux PC with Redhat 5)
--
Huib Intema (Jansky Fellow)
NRAO CV room 353 National Radio Astronomy Observatory
+1-434-244-6805 520 Edgemont Road
hintema at nrao.edu Charlottesville, VA 22903-2475
www.cv.nrao.edu/~hintema United States
--
More information about the Daip
mailing list