[Gate-users] DigiGate issue

[Philipp Matthies]

Dear fellow GATE users,

I'm having an issue with the DigiMode option of GATE: It seems it performs
(almost) a full new simulation instead of just adapting the digitizer
settings, thus defeating the whole purpose of this option.

I tried this with the example_SPECT so everybody can easily reproduce this.
I added this line to the output part in secondPart.mac:
/gate/output/root/setRootSinglesAdderFlag 1
Otherwise DigiMode wouldn't work properly.

I was sticking to the very short description here:
http://wiki.opengatecollaboration.org/index.php/Users_Guide_V7.2:How_to_run_Gate#How_to_launch_DigiGate

So the first step should be just running the simulation:

$ Gate < SPECT.mac

Why is the read input operator "<" used here? I simply replaced it with a
space as usual, otherwise Gate wouldn't stop running:

$ Gate SPECT.mac

This step takes 52s and I expect DigiMode to run much faster than this
since all the Hits are generated now.

Next steps are renaming the root file to gate.root, changing the digitizer
settings and root setFileName in secondPart.mac and running Gate in
DigiMode using this command:

$ Gate --d SPECT.mac

The time it takes for this step is 48s, a mere 8% speedup compared to
running a whole new simulation, which seems very little to me. The newly
created root file contains the trees with the changed parameters, so it
technically worked (root file size ~25% smaller this time). Also the number
of Hits is exactly the same, as expected.

I also found this e-mail in the mailing list history from July 2016
indicating that DigiMode should be much faster but no specifics were given:
----
Hi,
The DigiGate option is available in the GATE simulation just by typing Gate
--d in the Linux's terminal. To doing so, you are asked to run two cascade
simulations: (1) Running your main GATE simulation and producing a ROOT
file containing Hits information (there is really no need to produce other
outputs), then (2) Re-running the modified macro-file (modifications in the
digitizer module) and feeding the previous ROOT output into the Gate as an
input; in this step you are asked to run the GATE in Digi-mode (i.e.,
typing Gate --d). The latter will be run much more faster than the another.

Hint: It is recommended putting all the macro-files and the ROOT output
(produced in the first step) in a same directory.

Hope these help!
Hojjat
----

Thanks a lot for sharing your experiences with DigiMode and your
suggestions on how to fully exploit its potential.

Best regards,
Philipp Matthies

---
My setup:
Ubuntu 16.04 LTS
Geant4.10.02.p02
Root 5.34.36
Gate 7.2 (develop branch)
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