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<p>Folks,</p>
<p>Please find the minutes <a moz-do-not-send="true"
href="https://halldweb.jlab.org/wiki/index.php/HDGeant4_Meeting,_June_30,_2020#Minutes">here</a>
and below.</p>
<p> -- Mark</p>
<p>
</p>
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<h2 id="firstHeading" class="firstHeading" lang="en"><span
dir="auto">HDGeant4 Meeting, June 30, 2020, </span><span
class="mw-headline" id="Minutes">Minutes</span></h2>
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lang="en">
<p>Present: Alex Austregesilo, Sean Dobbs, Colin Gleason,
Mark Ito (chair), Igal Jaegle, Richard Jones, Simon
Taylor, Nilanga Wickramaarachchi
</p>
<p>There is a <a rel="nofollow" class="external text"
href="https://bluejeans.com/s/Ghdjw/">recording of
this meeting</a> on the BlueJeans site. Use your JLab
credentials to get access.
</p>
<h3><span class="mw-headline"
id="Announcement:_Version_Set_with_Upgraded_Geant4">Announcement:
Version Set with Upgraded Geant4</span></h3>
<p><a rel="nofollow" class="external text"
href="https://mailman.jlab.org/pipermail/halld-offline/2020-June/004104.html">A
new version set with upgrade to Geant4:
version_4.21.3.xml</a> was released today. Mark
described it and attendant caveats. This led to a
discussion of upgrading compilers.
</p>
<ul>
<li> We did not go further with Geant4 versions because
of limitations with the CentOS7 native compiler.</li>
<li> Similar issues may arise with ROOT.</li>
<li> There are three options to address the issue:
<ol>
<li> Do nothing and accept the limitations imposed
by the default GCC 4.8.5 compiler</li>
<li> Require users to use a container for all
software-dependent functions where the container
has a non-CentOS7-default version of the compiler
installed.</li>
<li> Require users to implement advanced compilers
on their systems either by
<ol>
<li> using a system like <a rel="nofollow"
class="external text"
href="https://www.softwarecollections.org/en/">Software
Collections</a></li>
<li> or installing more modern compiler versions
natively</li>
</ol>
</li>
</ol>
</li>
</ul>
<p>There are various use cases that may (or may not) need
support going forward, e.g., farm user at JLab,
developer on a private desktop or laptop machine,
maintainer of a university cluster, etc.
</p>
<p>We will have to return to this discussion at some
point.
</p>
<h3><span class="mw-headline"
id="Review_of_minutes_from_the_last_Meeting">Review of
minutes from the last Meeting</span></h3>
<p>We went over <a
href="https://halldweb.jlab.org/wiki/index.php/HDGeant4_Meeting,_June_16,_2020#Minutes"
title="HDGeant4 Meeting, June 16, 2020">the minutes
from June 16</a> without extensive comment.
</p>
<h3><span class="mw-headline" id="Issues_on_GitHub">Issues
on GitHub</span></h3>
<p>We reviewed <a rel="nofollow" class="external text"
href="https://github.com/JeffersonLab/HDGeant4/issues">the
issues</a>.
</p>
<h4><span class="mw-headline"
id="Energy_deposition_in_TOF_mismatch_in_data_.26_MC_.23159"><a
rel="nofollow" class="external text"
href="https://github.com/JeffersonLab/HDGeant4/issues/159">Energy
deposition in TOF mismatch in data & MC #159</a></span></h4>
<p>Sean cross-posted this issue from the halld_sim
repository to hdgeant4.
</p>
<h4><span class="mw-headline"
id="BCAL_reconstructed_energy_sometimes_broken_on_startup:_multicore_only_.23143"><a
rel="nofollow" class="external text"
href="https://github.com/JeffersonLab/HDGeant4/issues/143">BCAL
reconstructed energy sometimes broken on startup:
multicore only #143</a></span></h4>
<p>Richard reported progress on non-reproducible BCAL
energy results when running hdgeant4 with multiple
threads. He has discovered a pathology with the
"division" technique of Geant4 to create multiple
sensitive detector channels. HDGeant4 uses this feature
ubiquitously, not only in the BCAL but also in the CDC,
FCAL, TOF, etc. The implementation of divisions turns to
be manifestly non-thread-safe. Another technique, the
Geant4 "replica" feature, does have thread safety built
in and Richard has followed that code as a model for how
to implement thread safety for divisions.
</p>
<p>In the process, Richard identified a separate issue
where results from one events depend on details of how
processing proceed with previous events, an effect he is
calling hysteresis. This leads to non-reproducibility in
repeated execution of the code starting with the same
random number seeds each time. He believes the problem
lies in the code to do charged particle propagation
through magnetic fields.
</p>
<p>He concludes that all results to date of multi-threaded
running of HDGeant4 are suspect. Luckily, the running we
have been doing on the OSG has always been
single-threaded.
</p>
<h3><span class="mw-headline" id="Pull_Requests_on_GitHub">Pull
Requests on GitHub</span></h3>
<p>We looked over <a rel="nofollow" class="external text"
href="https://github.com/JeffersonLab/HDGeant4/pulls">the
pull requests</a>. Igal submitted <a rel="nofollow"
class="external text"
href="https://github.com/JeffersonLab/HDGeant4/pull/158">changes
to simulate the lead tungstate insert</a> for FCAL2.
He based his changes on work done by Simon. Simon
explained that, in terms of material, the insert is
implemented as a single block, but sub-divided to give
individual read-out channels following the scheme used
in the FCAL. The pull request has been merged.
</p>
<h3><span class="mw-headline" id="Action_Item_Review">Action
Item Review</span></h3>
<ol>
<li> Continue work on the BCAL multi-threading problem
(Richard)</li>
<li> Structure a discussion on advanced compiler
versions (Mark)</li>
<li> Try out the bcal_nolight_heavy_rtj branch. (Colin)</li>
<li> Merge issues #93 and #111 (Mark)</li>
</ol>
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