For detector design
studies or other work requiring a high event
production rate, detailed
simulations such as BgsApp are too slow. Typical rates for
B0B0bar using BgsApp are
around 5 seconds per event. The aim of a fast simulation is to increase
this rate by a factor
of ~100 to 1000. In general,
such an increase in speed comes at the expense of detector detail
or the
amount of information collected and stored for hits and tracks. Where
the
balance
between speed and detail is struck will be determined by the use to
which the code is put.
In order to avoid the need for several different
fast simulation executables.
To use the "Bogus" fast
simulation, you need to make a test release based on
release
14.0.3 or higher.
Basic
information for making a new release can be found here.
Then, add the following pakages with release
14.0.3:
BgsApp
V00-02-55
Bogus V00-07-27
BgsCEPack
V00-03-08
BgsDchSim
V00-02-24
BgsPepSim
V00-02-46
BgsSvtSim
V00-04-52
TrkBgsModules
V00-05-07
BgsEmcSim V00-03-31 work
under progress
EmcBgsModules V00-03-00 work
under progress
EmcPid
V00-04-22
BgsFwkModule
(default)
A description of the design
of the Emc for the fast simulation can be found here.
Other Useful Packages
After having created, compiled and linked the release, don't forget to
initialise objectivity
with simdevboot or setboot even if you don't intend to write to the
database as the simulation
program relies on the database to access many quantities related to the
various subdetectors.
(
An
extensive description on how to run the Monte Carlo simulation in the
general case can
be found here.)
Before trying to run the program, you have to set several variables
required to run Bogus
(Monte Carlo simulation in general can be found here)
in
BgsApp/fastbgs.env
. This is conveniently achieved by doing:
source
../BgsApp/fastbgs.env (assuming you are in
workdir)
BgsApp/fastbgs.env also enables the access to the fast simulation by
setting the variable
FASTMC to
"fast-param" to
run
the parameterized model or
"fast-model" for the so called
fast-model which is a
less detailed version of the detector simulation.
Not setting
FASTMC (
unsetenv FASTMC)
or setting it to
"bogus"
will run the
standard simulation program.
To run whichever simulation model just type from
workdir directory
BgsApp ../BgsApp/BgsUserExampleEvtGen.tcl
This will generate generic B events with EvtGen generator. Other Monte
Carlo generator (as usual)
can be accessed by the other BgsUserExampleXXXX.tcl or by simply
setting
UDECAY to the
appropriate
generator (not setting
UDECAY
generates BBbar event with EvtGen).
Parameters related to the
fast-simulation module by module:
As working example one should look at the settings of the Fast
Simulation in
BgsApp/BgsFastSim.tcl.
Here I will mainly talk about the various setting used in
BgsApp/BgsFastSim.tcl
as they are the ones
you are likely to modify.
Parameters in Bogus module:
- To interact with Bogus module
module
talk
Bogus
talkto Bogus {
parameter
set "value" or
parameter set
"value"
exit
}
- For the bogus fast simulation (called fast-sim):
So far only Pep (ie: beam pipe and support tube surrounding the SVT),
SVT and DCH have fast simulation modules.
Therefore for fast-simulation the following bogus option should be set:
talkto
Bogus {
pepModel set "fast-model" choose
the model coresponding to the Bogus fast simulation for Pep
svtModel set "fast-model" "
"
for SVT
dchModel set "fast-model" "
"
for DCH
emcModel set "none" turn
off the simulation of the Emc
drcModel set "none" turn
off the simulation of the Dirc
ifrModel set "none" turn
off the simulation of the Ifr
rangeCut set
10000 limit
secondary production, main speed improvement
}
- For the parametrized model (called fast-param)
This model is the fatest,
few
explanations about it can be found here (1).
Similarly to fast model, we ask bogus to use and activate parameters
specific to the parametrize model:
module
talk Bogus
FastParam set true Activate
the parametrize model (see 1 for detail)
pepModel set "none" Turn
off the simulation of the pep (see ##)
svtModel set "fast-param" Choose
the model coresponding to the parametrized model for the Svt
dchModel set "fast-param" Choose
the model coresponding to the parametrized model for the Dch
emcModel set "fast-CE-cylinder" Choose
the CEPack parametrized model for the EMC
emcEM set 1
(or 0) If
1 activate only the EM shower parameterization for e+ e- gamma
Otherwise
simulate also hadron assuming EMC a hadron calorimeter
drcModel set "none" Turn
off the simulation of the Dirc
ifrModel set "none" Turn
off the simulation of the Ifr
exit
(##) the simulation
of pep is not completely turn off. As it is the case for the
full simulation, the svt is embedded into pep volume
(however here it is an
empty space filled with vacuum to limit secondary
productions)
Another speed inprovement has been found by using a "Barrel"
modelisation of the
magnetic field
As we use here
G4VFastSimulationModel,
the
BgsTransportation
does not work
Instead we use G4Transportation.
we also talk to bogus to set those parameters:
module
talk Bogus
BFACField set "barrel" use
barrel modelisation of the magnetic field
useBgsTran set 0 use
G4Transportation instead of BgsTransportation
exit
Parameters in TrkBgsModules:
Several parameter which regulate the use of TrkBgsModules (where the
tracks
are reconstructed) are accessible from
BgsApp/BgsFastSim.tcl
(it is encouraged to put modification to the default setting in
BgsApp/BgsAppPatches.tcl). To "talk" to the reco modules:
module
talk TbmLoadVFTracking
talkto
TbmLoadVFTracking {
parameter
set "value" or
parameter set
"value"
exit
}
The paramaters used are:
verbose (boolean)
DoTheFit
(boolean) If set to true, the program use the Billoire
method to reconstruct the tracks
from the hits and to determine tracks paramater and error matrix.
otherwise the tracks informations is taken directly from the generator
level
makeTuple
(boolean) If set true will save tracks informations such as
tracks
parameter and their
error, pulls, error matrix. If not set no info written to ntuple.
HitsInfo
(boolean) (required
makeTuple set to true to be
effective)
If set
to true, will fill an ntuple on the hits containing variables
(ie
hit position, momentum, Pt, radiation length, path length, and
Id of the track to which it belongs).
It must be noted that it is time consuming, and should not
set to true
for
other purpose than debugging (it also takes a lots of space...
ie about
40 hits per particles)
svtResScale
(real) Those two
parameters are used to rescale the hit resolution (for svt and dch hits
dchResScale
(real) separately) by a
certain amount set through those parameter.
The Default is 1. (no rescaling)
Parameters in EmcBgsModules:
It must be mentionned that all list name can be change.
module
talk EmbmLoadVFCluster (the name of this module is about to
change)
parameter
set "value"
exit
In terms of parameter, only one can be altered for the moment:
DoOnlyNeutral (boolean)
If set to true, the EmcCand list will be filled with neutral candidates
only
Comparison between fast simulation
models and moose:
In order to compare between the
various models, 5000 generic BBbar events have been generated and
reconstructed using moose and both fast simulation models. The same
random seeds were used for the 3
models. This way, we insure a proper comparison since the same events
are generated for the 3 models
and only the track reconstruction differs. Plots were generated with
this
kumac file.
In terms of speed the Bogus fast model is relatively slow, some
improvement is achieved by limiting
the production of secondaries (
described
previously). The maximum speed which can be achieved is
of the order of
3 events per
second.
The parametrized model is much faster, in its current tuning it
processes about
55 events per
second counting
only the tracking and about
25 events per
second for producing
Beta Candidate with both charged and neutrals.
Example
of BetaCandidate Production with Parameterized Fast Simulation (
based on 5000 evts)
|
|
Bogus Fast Simulation
|
Parameterized Fast Simulation |
Tracking (Svt+Dch)
|
330 ms/evt (3 evt/s)
|
18 ms/evt (55 evt/s)
|
BgsEmcSim (BgsCEPack)*
|
|
9 ms/evt
(e+,e-,gamma) 21ms/evt (EM+all hadron)
|
Total Svt+Dch+Emc
|
|
27 ms/evt
(only EM shower) 40ms/evt (EM+all hadron)
|
TrkBgsModules
(track reco)
|
|
5 ms/evt (no
ntupling)
|
| EmcBgsModules
(Emc reco)* |
|
0.6 ms/evt (e+,e-,gamma)
0.85
ms/evt (EM+all hadron)
|
| LoadRecoBtaCandidates* |
|
1.75 ms/evt (e+,e-,gamma)
2.27 ms/evt (EM+all
hadron)
|
* work under progress
* standard module
Comparison plots between Bogus
fast simulation and moose:
- the green full circle is the Bogus
fast model
- the purple histo
line and full square are for moose
Comparison plots between the
parametrized model and moose:
- the green full circle is for the
parametrized model
- the purple histo
line and full square are for moose
Comparison plots between the Bogus
fast model and parametrized model:
- the green full circle is for the
Bogus fast model
- the purple histo
line and full square are for the parametrized model
Page author: Dominique J.
Mangeol
| Last significant update: 24 July
2003 |
