Import Geant4 11.4.0 source tree

2025-12-05 08:54:02 +01:00
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+//
+// ********************************************************************
+// * License and Disclaimer                                           *
+// *                                                                  *
+// * The  Geant4 software  is  copyright of the Copyright Holders  of *
+// * the Geant4 Collaboration.  It is provided  under  the terms  and *
+// * conditions of the Geant4 Software License,  included in the file *
+// * LICENSE and available at  http://cern.ch/geant4/license .  These *
+// * include a list of copyright holders.                             *
+// *                                                                  *
+// * Neither the authors of this software system, nor their employing *
+// * institutes,nor the agencies providing financial support for this *
+// * work  make  any representation or  warranty, express or implied, *
+// * regarding  this  software system or assume any liability for its *
+// * use.  Please see the license in the file  LICENSE  and URL above *
+// * for the full disclaimer and the limitation of liability.         *
+// *                                                                  *
+// * This  code  implementation is the result of  the  scientific and *
+// * technical work of the GEANT4 collaboration.                      *
+// * By using,  copying,  modifying or  distributing the software (or *
+// * any work based  on the software)  you  agree  to acknowledge its *
+// * use  in  resulting  scientific  publications,  and indicate your *
+// * acceptance of all terms of the Geant4 Software license.          *
+// ********************************************************************
+//
+// G4FunctionSolver
+//
+// Class description:
+//
+// Templated utility class to solve equation F(x) = 0 on interval [a, b]
+// Parameters of the class: tolerance - relative accuracy of the method,
+// maxIter - max number of iterations. User should provide a class with
+// only one method: T_Function::Function(G4double x). The main method
+// of the class is 'G4bool G4FunctionSolver::FindRoot(G4double& x)', where
+// user defines initial value x, which is modifided to be a final solution
+// of the equation.
+//
+// If the equation cannot be resolved with required accuracy FindRoot()
+// method returns "false".
+//
+// Parameters of the solver may be changed before the new call via Set
+// methods.
+//
+// Created 04.10.2025 V.Ivanchenko
+//  
+
+#ifndef G4FunctionSolver_h
+#define G4FunctionSolver_h 1
+
+#include "globals.hh"
+
+template <class T_Function> class G4FunctionSolver 
+{
+public:
+	
+  G4FunctionSolver(T_Function* ff, const G4int iterations, const G4double tol)
+    : maxIter(iterations), tolerance(tol), tF(ff) {};
+
+  // copy constructor	
+  G4FunctionSolver(const G4FunctionSolver& right) = delete;
+
+  // destructor
+  ~G4FunctionSolver() = default;
+	
+  // operators
+  G4FunctionSolver& operator=(const G4FunctionSolver& right) = delete;
+  G4bool operator==(const G4FunctionSolver& right) const = delete;
+  G4bool operator!=(const G4FunctionSolver& right) const = delete;
+
+  inline void SetMaxIterations(const G4int iterations)
+  { maxIter = iterations; }
+
+  inline void SetTolerance(const G4double epsilon)
+  { tolerance = epsilon; }
+
+  inline void SetIntervalLimits(const G4double Limit1, const G4double Limit2)
+  {
+    aa = std::min(Limit1, Limit2);
+    bb = std::max(Limit1, Limit2);
+  }
+
+  // Calculates the root of the equation Function(x)=0
+  inline G4bool FindRoot(G4double& x)
+  {
+    G4double a = aa;
+    G4double b = bb;
+
+    // check the interval before the start
+    x = std::min(std::max(x, a), b);
+
+    // check initial function
+    G4double fc = tF->Function(x);
+    if (0.0 == fc) { return true; }
+
+    // define accuracy in X
+    G4double epsX = tolerance*x;
+    // define accuracy in Y
+    G4double epsY = tolerance*fc;
+
+    // the interval is too small
+    if (std::abs(a - b) <= epsX)
+    {
+      x = 0.5*(a + b);
+      return true;
+    }
+
+    // check edges
+    G4double fa = tF->Function(a);
+    G4double fb = tF->Function(b);
+
+    // root should be inside interval
+    if (fa*fb >= 0.0)
+    {
+      x = (std::abs(fa) <= std::abs(fb)) ? a : b;
+      return (std::min(std::abs(fa), std::abs(fb)) < epsY);
+    }
+
+    // fa*fb < 0.0 - finding the root by iterative procedure, 
+    // the loop is completed if function is below epsY
+    // or if x become close to edges with accuracy epsX 
+    for (G4int i = 0; i < maxIter; ++i)
+    {
+      x = (a*fb - b*fa)/(fb - fa);
+      fc = tF->Function(x);
+      if (std::abs(fc) < epsY) { return true; }
+
+      G4double delta = std::min((x - a), (b - x));
+      if (delta < epsX) { return true; }
+      else if (fa*fc < 0.0) { b = x; fb = fc; }
+      else { a = x; fa = fc; }
+    }
+    // number of iterations exceed the limit
+    return false;
+  }
+
+private:
+
+  // maximum number of iterations
+  G4int maxIter;
+  // relative accuracy in X and Y
+  G4double tolerance;
+
+  // interval limits [a,b] 
+  G4double aa{0.0};
+  G4double bb{0.0};
+
+  T_Function* tF;
+};
+
+#endif