[ESPResSo-devel] [bug #44133] Temperature in LB_GPU is too high

[Joost de Graaf]

URL:
  <http://savannah.nongnu.org/bugs/?44133>

                 Summary: Temperature in LB_GPU is too high
                 Project: ESPResSo
            Submitted by: jdegraaf
            Submitted on: Fri 30 Jan 2015 04:08:59 PM GMT
                Category: Simulation core
                Severity: 4 - Important
                  Status: Confirmed
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 3.3.0
           Fixed Release: None

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Details:

(1) The particle temperature is too high; as determined by running a longer
version of the lb_gpu.tcl test case, see figure.
(2) The lb_gpu.tcl (and by extension the lb.tcl) test case uses the
instantaneous fluid temperature as its error criterion, this should be the
averaged fluid temperature.
(3) The lb fluid temperature may be too high; could not confirm, different
seeds gave different averages, see figure for an instance of a too high fluid
temperature.
(4) The lb gpu is improperly seeded; it uses global seed plus thread index. If
one uses the PID as global seed (as done in the test case) successive runs
produce systems with nearly identical progression of the kinetic energy.
(5) In the extended run length version of the lb_gpu.tcl test case there is
unexpected divergence of the kinetic energy (temperature) when runs are
initialized with identical seeds. They evolve identically at first, but
diverge suddenly somewhere between 16000 and 20000 steps (depending on the
seed and possibly time step), see attached images. This could be an
uninitialized memory issue.
(6) The deviation of the temperature with respect to the input value becomes
smaller with smaller time step. 



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File Attachments:


-------------------------------------------------------
Date: Fri 30 Jan 2015 04:08:59 PM GMT  Name: particle_temp_divergence_zoom.png
 Size: 96kB   By: jdegraaf

<http://savannah.nongnu.org/bugs/download.php?file_id=32949>
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Date: Fri 30 Jan 2015 04:08:59 PM GMT  Name: summary_temp_high.png  Size: 84kB
  By: jdegraaf

<http://savannah.nongnu.org/bugs/download.php?file_id=32950>

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