<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body style="overflow-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;">Dear Peter,<div><br></div><div>Thanks for quick answer! </div><div><br></div><div>Can you elaborate a bit more on a situation where this component is useful? I understand what you are saying, but still can’t get why would I want this? For example, if I have an ideal polarizer, normally it would just set P=1 for every trajectory in the unpolarized beam. With spin_random I would lose half of all trajectories after such a polarizer.</div><div><br></div><div>My general feeling is that trajectories were never meant to be identified as real neutrons, so I’m struggling to understand the rationale behind this component.</div><div><br></div><div>I’m running 3.5.24, I will check the fix, thanks!</div><div><br></div><div>Best regards,</div><div>PK<br id="lineBreakAtBeginningOfMessage"><div><br><blockquote type="cite"><div>On 2025. Apr 24., at 15:37, Peter Kjær Willendrup <pkwi@dtu.dk> wrote:</div><br class="Apple-interchange-newline"><div>
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Hi Peter,
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<div>On 24 Apr 2025, at 13.55, Петр Коник via mcstas-users <mcstas-users@mcstas.org> wrote:</div>
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<div>Can you explain me the intended use of Spin_random component? What are the benefits of assigning polarization to trajectories before the polarizer?
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<div>The component was mainly added to allow defining an “unpolarised beam” at the “full beam level” (i.e. with a set polarisation pr. ray but a net 0 polarisation) to allow comparing with all rays having sx=sy=sz=0 (i.e. with each ray unpolarised).</div>
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<div>Moreover, when used in combination with Pol_Vmirror component it results in polarization over 1 if two components are rotated 90 degrees relative to each other.<br>
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<div>We have recently made a fix to that component (i.e. ~ 1 month ago) that I would think rectifies this problem - see <a href="https://github.com/mccode-dev/McCode/commit/55e3989eb05150a7671523749f30dd462e19b266">https://github.com/mccode-dev/McCode/commit/55e3989eb05150a7671523749f30dd462e19b266</a>. </div>
<div>The logic is that a given polariser / analyser defines a definition of “up/down”, meaning post to “measurement” the other components should be put to zero.</div>
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<div>How recent a version are you running? Chances are that 3.5.25 (which is only on conda-forge at the moment) would fix this.</div>
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<div>Otherwise stay tuned for 3.5.26 that I can promote to become a “full” release including .deb packages, Windows installer etc.</div>
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<div>Best,</div>
<div>Peter W</div>
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Peter Kjær Willendrup<br>
Forskningsingeniør, Specialkonsulent<br>
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DTU Physics<br>
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