| Geant4 Cross Reference |
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26 //
27 // -------------------------------------------------------------------
28 // GEANT4 Class file
29 //
30 //
31 // File name: G4PolynomialPDF
32 //
33 // Author: Jason Detwiler (jasondet@gmail.com)
34 //
35 // Creation date: Aug 2012
36 //
37 // Description: Evaluates, generates random numbers from, and evaluates
38 // the inverse of a polynomial PDF, its CDF, and its first and second
39 // derivative.
40 //
41 // -------------------------------------------------------------------
42
43 #ifndef G4POLYNOMIALPDF_HH
44 #define G4POLYNOMIALPDF_HH
45
46 #include "globals.hh"
47 #include <vector>
48
49 class G4PolynomialPDF
50 {
51 public:
52 G4PolynomialPDF(size_t n = 0, const double* coeffs = nullptr,
53 G4double x1=0, G4double x2=1);
54
55 ~G4PolynomialPDF();
56 // Setters and Getters for coefficients
57 inline void SetNCoefficients(size_t n) { fCoefficients.resize(n); fChanged = true; }
58 inline size_t GetNCoefficients() const { return fCoefficients.size(); }
59 inline void SetCoefficients(const std::vector<G4double>& v) {
60 fCoefficients = v; fChanged = true; Simplify();
61 }
62 inline G4double GetCoefficient(size_t i) const { return fCoefficients[i]; }
63 void SetCoefficient(size_t i, G4double value, bool doSimplify);
64 void SetCoefficients(size_t n, const G4double* coeffs);
65 void Simplify();
66
67 // Set the domain over which random numbers are generated and over which
68 // the CDF is evaluated
69 void SetDomain(G4double x1, G4double x2);
70
71 // Normalize PDF to 1 over domain fX1 to fX2. Used internally by
72 // GetRandomX(), but the user may want to call this as well for evaluation
73 // purposes.
74 void Normalize();
75
76 // Evaluate (d/dx)^ddxPower f(x) (-1 <= ddxPower <= 2)
77 // ddxPower = -1 -> CDF;
78 // ddxPower = 0 -> PDF
79 // ddxPower = 1 -> PDF'
80 // ddxPower = 2 -> PDF''
81 G4double Evaluate(G4double x, G4int ddxPower = 0);
82
83 // Generate a random number from this PDF
84 G4double GetRandomX();
85
86 // Set the tolerance to within negative minima are checked
87 inline void SetTolerance(G4double tolerance) { fTolerance = tolerance; }
88
89 // Find a value x between x1 and x2 at which ddxPower[PDF](x) = p.
90 // ddxPower = -1 -> CDF;
91 // ddxPower = 0 -> PDF
92 // ddxPower = 1 -> PDF'
93 // (ddxPower = 2 not implemented)
94 // Solves analytically when possible, and otherwise uses the Newton-Raphson
95 // method to find the zero of ddxPower[PDF](x) - p.
96 // If not found in range, returns the nearest boundary.
97 // Beware that if x1 and x2 are not set carefully there may be multiple
98 // solutions, and care is not taken to select a particular one among them.
99 // Returns x2 on error
100 G4double GetX( G4double p, G4double x1, G4double x2, G4int ddxPower = 0,
101 G4double guess = 1.e99, G4bool bisect = true );
102 inline G4double EvalInverseCDF(G4double p) { return GetX(p, fX1, fX2, -1, fX1 + p*(fX2-fX1)); }
103 G4double Bisect( G4double p, G4double x1, G4double x2 );
104
105 void Dump();
106
107 protected:
108 // Checks for negative values between x1 and x2. Used by GetRandomX()
109 G4bool HasNegativeMinimum(G4double x1, G4double x2);
110
111 G4double fX1;
112 G4double fX2;
113 std::vector<G4double> fCoefficients;
114 G4bool fChanged;
115 G4double fTolerance;
116 G4int fVerbose;
117 };
118
119 #endif
120