[PWGEM,PWGEM-36] Pi0Flow: Reduce CPU time for LUT

- changed `lookupTable1D` from `std::vector` to `std::array` and fill with all good values when MapLevel is >= 4 for same event and background set in the config

Author: mhemmer-cern

PWGEM/PhotonMeson/Tasks/taskPi0FlowEMC.cxx

@@ -220,14 +220,14 @@ struct TaskPi0FlowEMC {
   o2::emcal::Geometry* emcalGeom;
   o2::emcal::BadChannelMap* mBadChannels;
   TH1D* h1SPResolution = nullptr;
-  // Constants for eta and phi ranges
-  double etaMin = -0.75, etaMax = 0.75;
-  int nBinsEta = 150; // 150 bins for eta
+  // Constants for eta and phi ranges for the look up table
+  static constexpr double etaMin = -0.75, etaMax = 0.75;
+  static constexpr int nBinsEta = 150; // 150 bins for eta
 
-  double phiMin = 1.35, phiMax = 5.75;
-  int nBinsPhi = 440; // (440 bins = 0.01 step size covering most regions)
+  static constexpr double phiMin = 1.35, phiMax = 5.75;
+  static constexpr int nBinsPhi = 440; // (440 bins = 0.01 step size covering most regions)
 
-  std::vector<int8_t> lookupTable1D;
+  std::array<int8_t, nBinsEta * nBinsPhi> lookupTable1D;
   float epsilon = 1.e-8;
 
   // static constexpr
@@ -437,7 +437,8 @@ struct TaskPi0FlowEMC {
     }
 
     if (cfgDoM02.value) {
-      registry.add("hSparseFlow", "THn for SP", HistType::kTHnSparseF, {thnAxisM02, thnAxisPt, thnAxisCent});
+      registry.add("p3DM02Flow", "<v_n> vs M_{02} vs p_T vs cent", HistType::kTProfile3D, {thnAxisM02, thnAxisPt, thnAxisCent});
+      registry.add("h3DSparsePi0", "M_{02} vs p_T vs cent", HistType::kTH3D, {thnAxisM02, thnAxisPt, thnAxisCent});
     }
 
     ccdb->setURL(ccdbUrl);
@@ -663,28 +664,33 @@ struct TaskPi0FlowEMC {
     emcalGeom = o2::emcal::Geometry::GetInstanceFromRunNumber(collision.runNumber());
     // Load Bad Channel map
     mBadChannels = ccdb->getForTimeStamp<o2::emcal::BadChannelMap>("EMC/Calib/BadChannelMap", collision.timestamp());
-    lookupTable1D = std::vector<int8_t>(nBinsEta * nBinsPhi, -1);
+    lookupTable1D.fill(-1);
     double binWidthEta = (etaMax - etaMin) / nBinsEta;
     double binWidthPhi = (phiMax - phiMin) / nBinsPhi;
 
-    for (int iEta = 0; iEta < nBinsEta; ++iEta) {
-      double etaCenter = etaMin + (iEta + 0.5) * binWidthEta;
-      for (int iPhi = 0; iPhi < nBinsPhi; ++iPhi) {
-        double phiCenter = phiMin + (iPhi + 0.5) * binWidthPhi;
-        try {
-          // Get the cell ID
-          int cellID = emcalGeom->GetAbsCellIdFromEtaPhi(etaCenter, phiCenter);
-
-          // Check conditions for the cell
-          if (isTooCloseToEdge(cellID, 1)) {
-            lookupTable1D[getIndex(iEta, iPhi)] = 2; // Edge
-          } else if (isCellMasked(cellID)) {
-            lookupTable1D[getIndex(iEta, iPhi)] = 1; // Bad
-          } else {
-            lookupTable1D[getIndex(iEta, iPhi)] = 0; // Good
+    if (cfgEMCalMapLevelBackground.value >= 4 && cfgEMCalMapLevelSameEvent >= 4) {
+      // in this case we do not want to check the clusters, so just say thery are all good.
+      lookupTable1D.fill(0); // good
+    } else {
+      for (int iEta = 0; iEta < nBinsEta; ++iEta) {
+        double etaCenter = etaMin + (iEta + 0.5) * binWidthEta;
+        for (int iPhi = 0; iPhi < nBinsPhi; ++iPhi) {
+          double phiCenter = phiMin + (iPhi + 0.5) * binWidthPhi;
+          try {
+            // Get the cell ID
+            int cellID = emcalGeom->GetAbsCellIdFromEtaPhi(etaCenter, phiCenter);
+
+            // Check conditions for the cell
+            if (isTooCloseToEdge(cellID, 1)) {
+              lookupTable1D[getIndex(iEta, iPhi)] = 2; // Edge
+            } else if (isCellMasked(cellID)) {
+              lookupTable1D[getIndex(iEta, iPhi)] = 1; // Bad
+            } else {
+              lookupTable1D[getIndex(iEta, iPhi)] = 0; // Good
+            }
+          } catch (o2::emcal::InvalidPositionException& e) {
+            lookupTable1D[getIndex(iEta, iPhi)] = 3; // Outside geometry
           }
-        } catch (o2::emcal::InvalidPositionException& e) {
-          lookupTable1D[getIndex(iEta, iPhi)] = 3; // Outside geometry
         }
       }
     }
@@ -1433,7 +1439,8 @@ struct TaskPi0FlowEMC {
           scalprodCand = scalprodCand / h1SPResolution->GetBinContent(h1SPResolution->FindBin(cent + epsilon));
         }
         if (cfgDoM02.value) {
-          registry.fill(HIST("hSparseFlow"), photon.m02(), photon.pt(), cent, scalprodCand);
+          registry.fill(HIST("p3DM02Flow"), photon.m02(), photon.pt(), cent, scalprodCand);
+          registry.fill(HIST("h3DSparsePi0"), photon.m02(), photon.pt(), cent);
         }
         return;
       } // end of loop over single cluster