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Dear Eric Greisen,</div>
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I understand the meaning of closures in the task of EVAUV.</div>
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Thanks,</div>
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Miyoshi</div>
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<div id="divRplyFwdMsg" dir="ltr"><span style="font-family: Calibri, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);"><b>$B:9=P?M(B:</b> Eric Greisen <egreisen@nrao.edu><br>
<b>$BAw?.F|;~(B:</b> 2024$BG/(B8$B7n(B8$BF|(B 1:13<br>
<b>$B08@h(B:</b> Makoto Miyoshi <makoto.miyoshi@nao.ac.jp><br>
<b>CC:</b> daip <daip@nrao.edu><br>
<b>$B7oL>(B:</b> Re: about the task EVAUV {External}</span>
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You are mis-reading the help file. The closure computation is done on the GAIN data, which is the observed divided by the model, not subtracted. And it is true that closure phase and amplitude of the observed data and of the model data will be different than
the same parameters of the GAIN file. The task is simply trying to report how close the model is to the observations. The statistics of the GAIN file are used to evaluate how well particular sources meet the requirements of calibration sources. I am adding
the following paragraph to the EVAUV help file:</div>
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The use of closure statistics to evaluate potential calibration</div>
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sources is discussed in detail in the paper Xu, M.H., Anderson,</div>
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J.M., Heinkelmann, R., Lunz, S., Schuh, H., Wang, G.L., 2019,</div>
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"Structure Effects for 3417 Celestial Reference Frame Radio</div>
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Sources", Ap. J. Suppl., 242:5. Available via:</div>
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<a href="https://doi.org/10.3847/1538-4365/ab16ea" id="OWA65f5b169-0490-3237-418d-10d66c6a7c49" class="OWAAutoLink" data-auth="NotApplicable">
https://doi.org/10.3847/1538-4365/ab16ea</a></div>
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Eric Greisen</div>
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<div id="x_divRplyFwdMsg" dir="ltr"><span style="font-family: Calibri, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);"><b>From:</b> Makoto Miyoshi <makoto.miyoshi@nao.ac.jp><br>
<b>Sent:</b> Wednesday, August 7, 2024 1:16 AM<br>
<b>To:</b> Eric Greisen <egreisen@nrao.edu><br>
<b>Cc:</b> daip <daip@nrao.edu><br>
<b>Subject:</b> about the task EVAUV {External}</span>
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Dear Sirs,</div>
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I am emailing because I have a question about the closure residual calculation in EVAUV.</div>
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The description of the task, EVAUV, states the following:</div>
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"The task will now compute and report closure phase and$B!!(Bamplitude statistics from the "visibilties" of the gain data set (produced by division of the input data by the model, not subtracting (1,0))."</div>
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http://www.aips.nrao.edu/cgi-bin/ZXHLP2.PL?EVAUV</div>
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In other words, it can be understood for me that at first make the difference between the observed visibility and the visibility corresponding to the image is calculated, and then the closures are calculated from the difference visibilities.</div>
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Wouldn't that give a different result than the case we calculated the closures from each of the observed visibilities, visibilities that corresponding to the model image, and then find the mean and standard deviation from the difference between them?</div>
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It is confirmed that this is different from the statistics of the difference between the closure phases output using CLPLT from the observed data and those corresponding to a model image.</div>
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One of them seems to be wrong. If my understanding is wrong, I am sorry.</div>
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Yours sincerely</div>
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Makoto Miyoshi</div>
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NAOJ, Mitaka</div>
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