Seeding improvements of digitizers

Allows for fully reproducible digitization, given same seed.

Author: sawenzel

Common/SimConfig/include/SimConfig/DigiParams.h

@@ -33,6 +33,7 @@ struct DigiParams : public o2::conf::ConfigurableParamHelper<DigiParams> {
   int maxOrbitsToDigitize = -1;                       // Digitizer can use this to truncate digits that fall beyond an orbit limit (relative to start of digization) given by this param; -1 means no limit imposed
                                                       // This parameter should typically be set to coincide with a single timeframe length or multiples thereof.
   std::string passName = "unanchored";                // passName for anchored MC
+  int seed = 0;                                       // rndSeed to be applied in digitization; convention is that 0 is time based
   O2ParamDef(DigiParams, "DigiParams");
 };
 

Detectors/Base/src/BaseDPLDigitizer.cxx

@@ -16,6 +16,7 @@
 #include <DetectorsBase/Propagator.h>
 #include <fairlogger/Logger.h>
 #include <TGeoGlobalMagField.h>
+#include <TRandom.h>
 
 using namespace o2::base;
 
@@ -54,6 +55,10 @@ void BaseDPLDigitizer::init(o2::framework::InitContext& ic)
     }
   }
 
+  // initialize the global ROOT random number generator (needed or not)
+  LOG(info) << "Initializing ROOT digitizer random with seed " << o2::conf::DigiParams::Instance().seed;
+  gRandom->SetSeed(o2::conf::DigiParams::Instance().seed);
+
   // finally call specific init
   this->initDigitizerTask(ic);
 }

Detectors/EMCAL/simulation/src/Digitizer.cxx

@@ -25,6 +25,7 @@
 #include <fairlogger/Logger.h> // for LOG
 #include "CommonDataFormat/InteractionRecord.h"
 #include "CommonUtils/TreeStreamRedirector.h"
+#include "SimConfig/DigiParams.h"
 
 ClassImp(o2::emcal::Digitizer);
 
@@ -37,7 +38,11 @@ using namespace o2::emcal;
 void Digitizer::init()
 {
   mSimParam = &(o2::emcal::SimParam::Instance());
-  mRandomGenerator = new TRandom3(std::chrono::high_resolution_clock::now().time_since_epoch().count());
+  auto randomSeed = std::chrono::high_resolution_clock::now().time_since_epoch().count();
+  if (o2::conf::DigiParams::Instance().seed != 0) {
+    randomSeed = o2::conf::DigiParams::Instance().seed;
+  }
+  mRandomGenerator = new TRandom3(randomSeed);
 
   float tau = mSimParam->getTimeResponseTau();
   float N = mSimParam->getTimeResponsePower();

Detectors/EMCAL/simulation/src/DigitsVectorStream.cxx

@@ -19,14 +19,18 @@
 #include "EMCALSimulation/LabeledDigit.h"
 #include "EMCALSimulation/DigitsVectorStream.h"
 #include "CommonConstants/Triggers.h"
+#include "SimConfig/DigiParams.h"
 
 using namespace o2::emcal;
 
 void DigitsVectorStream::init()
 {
   mSimParam = &(o2::emcal::SimParam::Instance());
-
-  mRandomGenerator = new TRandom3(std::chrono::high_resolution_clock::now().time_since_epoch().count());
+  auto randomSeed = std::chrono::high_resolution_clock::now().time_since_epoch().count();
+  if (o2::conf::DigiParams::Instance().seed != 0) {
+    randomSeed = o2::conf::DigiParams::Instance().seed;
+  }
+  mRandomGenerator = new TRandom3(randomSeed);
 
   mRemoveDigitsBelowThreshold = mSimParam->doRemoveDigitsBelowThreshold();
   mSimulateNoiseDigits = mSimParam->doSimulateNoiseDigits();