Testing and Performance of starsim
We want to compare results and performace of the
starsim application to the staf. In addition,
we have both gcc and icc compilers availble when
building starsim, so we have to compare those
versions of the executable as well.
Tests were done with the STAR geometry y2004,
current as of March 4, 2004. The columns in the
following tables are marked with "opt" (optimized version)
and "noopt" (not optimized version). Note that
staf was linked to the not-optimized version
of the Geant libraries, for historical reasons.
We observe that the icc compiler may yield approximately 20% increase
in performace with respect to the gcc.
||staf (opt)||starsim gcc (noopt)||starsim icc (noopt)||starsim gcc (opt)||starsim icc (opt)
|A single muon event (based on 1k sample)
||Single AuAu200 event (averaged over 2 events)
2. Event by event comparison
a) Single muon hit test
In order to spot potential differences, we
shot a particle (muon) through the y2004 geometry,
using the old staf application, and the
new executables compiled with icc (intel 80) and gcc 3.2 compilers.
The random number seed was set to same value in all
tests. The output was captured in files:
We observe that while gcc-compiled starsim produces results
identical to icc, the old staf executable produces similar,
yet slightly different results (a few extra hits in the calorimeter).
This can be explained as a consequence of starsim being linked to the newer
version of Geant 3.21 libraries, and also having incremental code changes
b) Omega decays
Comparing omega decays as simulated with gcc and icc based versions
of starsim, we see slight difference in the actual simulated
It is likely that the source of this is the round-off error quantization. Different compilers
can prudce results that are slightly different, in the sixth or seventh
decimal place, triggering different branches of logic.
Summary: the results coming from staf and the two versions of starsim are different when looked
at on the event-by-event basis, necessitating a statistical comparison.
3. Statistical comparison (validation)
a) Gamma conversion study
We look at the rate of gamma conversion in the fixed geometry (y2003b) and
also at the momentum conservation in such process. The photons
were created using the command:
gkine 1 1 0.1 3 -2 2.
The plots produced look like this:
and represent the difference between the momentum of the gamma and the
total momentum of the e+e- pair created in a conversion. The plots
are available here:
Summary: the results coming from staf and the two versions of starsim are in
fact compatible, demostrating same conversion rate and numerical
characteristics of the momenta of the e+e- pairs.
b) Lambda decays
This allows to check the branching ratio as well as spectra.
The lambdas were created using the command:
gkine 1 18 0.1 1 -2 2.
Here's an example of the resulting pt distribution for
And for the complete set of plots:
Summary: the results coming from staf and the two versions of starsim are
compatible, demostrating the same (correct) branching ratios and numerical
characteristics of the momenta of the decays products.
c) Barrel EMC response
We would like to check the response of the barrel calorimeter,
as a useful regerssion test.
The electrons were created using the command:
gkine 1 3 1 1 0.1 0.2.
Here's an example of the resulting Barrel EMC signal distribution:
Comparison of the spectra claculated with
that the results are virtually same.
Last updated by Maxim Potekhin on 11/05/2004