helper to get nominal L3 field (#7506)

Author: jgrosseo

DataFormats/Parameters/include/DataFormatsParameters/GRPObject.h

@@ -82,6 +82,7 @@ class GRPObject
   void setL3Current(o2::units::Current_t v) { mL3Current = v; }
   void setDipoleCurrent(o2::units::Current_t v) { mDipoleCurrent = v; }
   void setFieldUniformity(bool v) { mUniformField = v; }
+  int8_t getNominalL3Field();
   /// getter/setter for data taking period name
   const std::string& getDataPeriod() const { return mDataPeriod; }
   void setDataPeriod(const std::string v) { mDataPeriod = v; }
@@ -158,14 +159,17 @@ class GRPObject
   bool mUniformField = false;                 ///< uniformity of magnetic field
   float mBeamEnergyPerZ = 0.f;                ///< beam energy per charge (i.e. sqrt(s)/2 for pp)
 
+  int8_t mNominalL3Field = 0;        //!< Nominal L3 field deduced from mL3Current
+  bool mNominalL3FieldValid = false; //!< Has the field been computed (for caching)
+
   int mBeamAZ[beamDirection::NBeamDirections] = {0, 0}; ///< A<<16+Z for each beam
 
   int mRun = 0;                 ///< run identifier
   int mFill = 0;                ///< fill identifier
   std::string mDataPeriod = ""; ///< name of the period
   std::string mLHCState = "";   ///< machine state
 
-  ClassDefNV(GRPObject, 5);
+  ClassDefNV(GRPObject, 6);
 };
 
 //______________________________________________
@@ -176,6 +180,18 @@ inline float GRPObject::getBeamZ2A(beamDirection b) const
   return a ? getBeamZ(b) / static_cast<float>(a) : 0.f;
 }
 
+//______________________________________________
+inline int8_t GRPObject::getNominalL3Field()
+{
+  // compute nominal L3 field in kG
+
+  if (mNominalL3FieldValid == false) {
+    mNominalL3Field = std::lround(5.f * mL3Current / 30000.f);
+    mNominalL3FieldValid = true;
+  }
+  return mNominalL3Field;
+}
+
 } // namespace parameters
 } // namespace o2