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<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Hi all,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">After some additional tests, Jan Wagner proposed that actually DiFX 2.6.3 and associated tools is working fine. Instead, the most likely explanation seems to be that
Ny is actually not recording R-pol as advertised, but instead linear (Horizontal, X in fourfit) polarisation. This fits both my Ny-Ns-Nn results (fringes to other stations with R-pol or X-pol, but not Y-pol) and also Jans notes from
</span><span style="font-size:11.0pt;mso-fareast-language:EN-US">r11112</span><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US"> where Ny gets alternating fringes to X or Y pol at international-baseline-stations, presumably due to differential
feed rotation.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">So, my issue appears to not be a DiFX issue, but rather a Ny-polarisation issue.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Kind regards<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Eskil<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><b><span style="font-size:12.0pt;color:black">From:
</span></b><span style="font-size:12.0pt;color:black">Eskil Varenius <eskil.varenius@chalmers.se><br>
<b>Date: </b>Sunday, 13 August 2023 at 20:33<br>
<b>To: </b>Adam Deller <adeller@astro.swin.edu.au><br>
<b>Cc: </b>difx-users@nrao.edu <difx-users@nrao.edu><br>
<b>Subject: </b>Re: [Difx-users] Lack of mixed-mode fringes with 2.6.3, then segfault with 2.8.1? {External}<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Hey Adam,</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Jan Wagner and Walter Brisken both offered to check, and concluded the segfault is a bug in 2.8.1 which was then fixed in the repo later. So the official 2.8.1 release
has a confirmed bug causing a segfault in vex2difx. Jan wrote: <br>
</span><span style="font-size:11.0pt;color:#1D1D1D;background:white">The fix was r10990 (trunk) and r10991 (2.8): "vex2difx.cpp fix segfault </span><span style="font-size:11.0pt;color:#1D1D1D"><br>
<span style="background:white">caused by missing realloc() of freqOffset[] and recFreqDestId[] - the </span><br>
<span style="background:white">associated code in vex2difx fixDatastreamTable() should really be moved into </span><br>
<span style="background:white">difxio".</span></span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Pulling the trunk version sorted this, but there are other issues. Ufortunately, my attempts to correlate the data to get at my original problem – lack of fringes at
one specific baseline and polarisation combination – did not get further with 2.8.1 or trunk. My datastream formats get misinterpreted some how to wrong values, despite working with with 2.6.3 vex2difx. I tried some combinations of vex2difx, startdifx, and
difx2mark4 from 2.6.3 and 2.8.1 with –override-version but so far no solution. </span>
<o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Simon C at OSO offered to look into the matter a bit more with the data we have, so I’ll await his findings and then maybe ask here again for additional advice.</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Kind regards</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Eskil</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US"> </span><o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><b><span style="font-size:12.0pt;color:black">From:
</span></b><span style="font-size:12.0pt;color:black">Adam Deller <adeller@astro.swin.edu.au><br>
<b>Date: </b>Sunday, 13 August 2023 at 13:03<br>
<b>To: </b>Eskil Varenius <eskil.varenius@chalmers.se><br>
<b>Cc: </b>difx-users@nrao.edu <difx-users@nrao.edu><br>
<b>Subject: </b>Re: [Difx-users] Lack of mixed-mode fringes with 2.6.3, then segfault with 2.8.1? {External}</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:11.0pt">Hey Eskil,</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:11.0pt">Have you tried vex2difx -v -v and/or valgrind vex2difx to see where the segfault is occurring? Obviously, it shouldn't be segfaulting, so presumably finding that and fixing it should go a fair way towards
solving the problem.</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:11.0pt">Cheers,</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:11.0pt">Adam</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:11.0pt">On Sat, 12 Aug 2023 at 04:22, Eskil Varenius via Difx-users <<a href="mailto:difx-users@listmgr.nrao.edu">difx-users@listmgr.nrao.edu</a>> wrote:</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt">Dear Difx-users,</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt">Background: I have mixed-mode continuum data from 3 stations: Ns(16 MHz VDIF), Ny(16 MHz M5B), Nn 32 MHz VDIF). Ns and Ny observe standard S/X with
R-pol only, and Nn (VGOS) observe dual linear X/Y (strictly speaking H/V but I'm using X/Y here since that's the VEX labels). Correlating Ns-Ny baseline with DiFX 2.6.3, is all good. I use zoom windows (to get 16 MHz from all stations) and FreqId selection
(to only correlate X-band and skip S-band channels). But when trying to correlate all three stations I run into problems.
</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt">Problem 1: With DiFX 2.6.3 I can correlate all three stations, and then run difx2mark4. Fourfit then gives me nice fringes on the Ns-Ny baseline (R-R
pol), and the Ns-Nn baseline (RX and RY pol). But while I do get nice XR fringes on the Nn-Ny baseline, I do not get any YR fringes on this baseline. I know the data are good, since I get fringes to these polarisations on another baseline. So I suspect I have
fallen into the "Warning: Limited support for mixed-mode..." here, or do you have other suggestions?
</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt">I saw there are improvements for mixed-mode in DiFX 2.8.1, so I decided to try it, but:</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt">Problem 2: With DiFX 2.8.1, I get "segfault" when I run
</span><span lang="EN-US" style="font-size:11.0pt">”</span><span style="font-size:11.0pt">vex2difx</span><span lang="EN-US" style="font-size:11.0pt">” (this worked with 2.6.3)</span><span style="font-size:11.0pt">. Any ideas?</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt">I guess hunting the "segfault in 2.8.1" is the most profitable route for the future? If so, please let me know what info you may need to speculate
further. I am happy to share output, v2d, vex, and even raw data for one scan for someone to reproduce this if you would be so kind to help.</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt">I am very puzzled by this!</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt">Kind regards</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt">Eskil</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:11.0pt">_______________________________________________<br>
Difx-users mailing list<br>
<a href="mailto:Difx-users@listmgr.nrao.edu" target="_blank">Difx-users@listmgr.nrao.edu</a><br>
<a href="https://listmgr.nrao.edu/mailman/listinfo/difx-users" target="_blank">https://listmgr.nrao.edu/mailman/listinfo/difx-users</a></span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:9.5pt">!=============================================================!</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:9.5pt">Prof. Adam Deller </span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:9.5pt">Centre for Astrophysics & Supercomputing </span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:9.5pt">Swinburne University of Technology <br>
John St, Hawthorn VIC 3122 Australia</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:9.5pt">phone: +61 3 9214 5307</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:9.5pt">fax: +61 3 9214 8797</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:9.5pt">!=============================================================!</span><o:p></o:p></p>
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