Import Geant4 11.0.0.beta source tree

source/processes/electromagnetic/utils/src/G4EmElementSelector.cc

@@ -65,9 +65,8 @@ G4EmElementSelector::G4EmElementSelector(G4VEmModel* mod,
   theElementVector = material->GetElementVector();
   if(nElmMinusOne > 0) {
     xSections.reserve(n);
-    G4PhysicsLogVector* v0 = new G4PhysicsLogVector(lowEnergy,highEnergy,nbins);
+    G4PhysicsLogVector* v0 = new G4PhysicsLogVector(lowEnergy,highEnergy,nbins,false);
     xSections.push_back(v0);
-    v0->SetSpline(false);
     for(G4int i=1; i<n; ++i) {
       G4PhysicsLogVector* v = new G4PhysicsLogVector(*v0);
       xSections.push_back(v);
@@ -146,6 +145,43 @@ void G4EmElementSelector::Initialise(const G4ParticleDefinition* part,
   //    << G4endl;
 }
 
+//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.....
+
+const G4Element*
+G4EmElementSelector::SelectRandomAtom(const G4double e, const G4double loge) const
+{
+  const G4Element* element = (*theElementVector)[nElmMinusOne];
+  if (nElmMinusOne > 0) {
+    // 1. Determine energy index (only once)
+    const size_t nBins  = (xSections[0])->GetVectorLength();
+    // handle cases below/above the enrgy grid (by ekin, idx that gives a=0/1)
+    // ekin = x[0]   if e<=x[0]   and idx will be   0 ^ a=0 => so y=y0
+    // ekin = x[N-1] if e>=x[N-1] and idx will be N-2 ^ a=1 => so y=y_{N-1}
+    const G4double ekin = std::max((xSections[0])->Energy(0),
+                                   std::min((xSections[0])->Energy(nBins-1),e));
+    // compute the lower index of the bin (idx \in [0,N-2] will be guaranted)
+    const size_t    idx = (xSections[0])->ComputeLogVectorBin(loge);
+    // 2. Do the linear interp.(robust for corner cases through ekin, idx and a)
+    const G4double   x1 = (xSections[0])->Energy(idx);
+    const G4double   x2 = (xSections[0])->Energy(idx+1);
+    // note: all corner cases of the previous methods are covered and eventually
+    //       gives a=0/1 that results in y=y0\y_{N-1} if e<=x[0]/e>=x[N-1] or
+    //       y=y_i/y_{i+1} if e<x[i]/e>=x[i+1] due to small numerical errors
+
+    const G4double    a = std::max(0., std::min(1., (ekin - x1)/(x2 - x1)));
+    const G4double urnd = G4UniformRand();
+    for (G4int i = 0; i < nElmMinusOne; ++i) {
+      const G4double  y1 = (*xSections[i])[idx];
+      const G4double  y2 = (*xSections[i])[idx+1];
+      if (urnd <= y1 + a*(y2-y1)) {
+        element = (*theElementVector)[i];
+        break;
+      }
+    }
+  }
+  return element;
+}
+
 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
 
 void G4EmElementSelector::Dump(const G4ParticleDefinition* part)