ROOT   6.10/09 Reference Guide
BrentMinimizer1D.h
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1 // @(#)root/mathcore:$Id$
2 // Author: David Gonzalez Maline 2/2008
3  /**********************************************************************
4  * *
5  * Copyright (c) 2004 Maline, CERN/PH-SFT *
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23
24 // Header file for class BrentMinimizer1D
25 //
26 // Created by: Maline at Mon Feb 4 09:32:36 2008
27 //
28 //
29
30
31 #ifndef ROOT_Math_BrentMinimizer1D
32 #define ROOT_Math_BrentMinimizer1D
33
34 #include "Math/IMinimizer1D.h"
35
36 #include "Math/IFunctionfwd.h"
37
38
39 namespace ROOT {
40 namespace Math {
41
42 //___________________________________________________________________________________________
43 /**
44  User class for performing function minimization
45
46  It will use the Brent Method for function minimization in a given interval.
47  First, a grid search is used to bracket the minimum value
48  with the a step size = (xmax-xmin)/npx. The step size
49  can be controlled via the SetNpx() function. A default value of npx = 100 is used.
50  The default value con be changed using the static method SetDefaultNpx.
51  If the function is unimodal or if its extrema are far apart, setting the fNpx to
52  a small value speeds the algorithm up many times.
53  Then, Brent's method is applied on the bracketed interval.
54  If the Brent method fails to converge the bracketing is repeted on the latest best estimate of the
55  interval. The procedure is repeted with a maximum value (default =10) which can be set for all
56  BrentRootFinder classes with the method SetDefaultNSearch
57
58
59
60  This class is implemented from TF1::GetMinimum.
61
62  To use the class, three steps have to be taken:
63  1. Create the class.
64  2. Set a function within an interval to look for the minimum.
65  3. Call the Minimize function with the error parameters.
66
67  If another minimization is to be performed, repeat the last two steps.
68
69  @ingroup Min1D
70
71  */
72
74
75  public:
76
77  /** Default Constructor. */
79
80  /** Default Destructor. */
81  virtual ~BrentMinimizer1D() {}
82
83  public:
84
85  /** Return current estimate of the position of the minimum. */
86  virtual double XMinimum() const { return fXMinimum; }
87
88  /** Return current lower bound of the minimization interval. */
89  virtual double XLower() const { return fXMin; }
90
91  /** Return current upper bound of the minimization interval. */
92  virtual double XUpper() const { return fXMax; }
93
94  /** Return function value at current estimate of the minimum. */
95  virtual double FValMinimum() const;
96
97  /** Return function value at current lower bound of the minimization interval. */
98  virtual double FValLower() const;
99
100  /** Return function value at current upper bound of the minimization interval. */
101  virtual double FValUpper() const;
102
103  /** Find minimum position iterating until convergence specified by the absolute and relative tolerance or
104  the maximum number of iteration is reached.
105  Return true if iterations converged successfully
106  \@param maxIter maximum number of iterations.
107  \@param absTol desired absolute error in the minimum position (default 1.E-8)
108  \@param absTol desired relative error in the minimum position (default = 1.E-10)
109  */
110  virtual bool Minimize( int maxIter, double absTol = 1.E-8, double relTol = 1.E-10);
111
112  /** Return number of iteration used to find minimum */
113  virtual int Iterations() const { return fNIter; }
114
115  /** Return name of minimization algorithm ("BrentMinimizer1D") */
116  virtual const char * Name() const;
117
118  /** Sets function to be minimized.
119
120  \@param f Function to be minimized.
121  \@param xlow Lower bound of the search interval.
122  \@param xup Upper bound of the search interval.
123  */
124  void SetFunction(const ROOT::Math::IGenFunction& f, double xlow, double xup);
125
126  /** Set the number of point used to bracket root using a grid */
127  void SetNpx(int npx) { fNpx = npx; }
128
129  /**
130  Set a log grid scan (default is equidistant bins)
131  will work only if xlow > 0
132  */
133  void SetLogScan(bool on) { fLogScan = on; }
134
135
136  /** Returns status of last estimate. If = 0 is OK */
137  int Status() const { return fStatus; }
138
139  // static function used to modify the default parameters
140
141  /** set number of default Npx used at construction time (when SetNpx is not called)
142  Default value is 100
143  */
144  static void SetDefaultNpx(int npx);
145
146  /** set number of times the bracketing search in combination with is done to find a good interval
147  Default value is 10
148  */
149  static void SetDefaultNSearch(int n);
150
151  private:
152
153  const IGenFunction* fFunction; // Pointer to the function.
154  bool fLogScan; // flag to control usage of a log scan
155  int fNIter; // Number of iterations needed for the last estimation.
156  int fNpx; // Number of points to bracket minimum with grid (def is 100)
157  int fStatus; // Status of code of the last estimate
158  double fXMin; // Lower bound of the search interval.
159  double fXMax; // Upper bound of the search interval
160  double fXMinimum; // Position of the stimated minimum.
161
162  }; // end class BrentMinimizer1D
163
164 } // end namespace Math
165
166 } // end namespace ROOT
167
168 #endif /* ROOT_Math_BrentMinimizer1D */
virtual ~BrentMinimizer1D()
Default Destructor.
Interface (abstract class) for generic functions objects of one-dimension Provides a method to evalua...
Definition: IFunction.h:134
int Status() const
Returns status of last estimate.
const double absTol
virtual double XUpper() const
Return current upper bound of the minimization interval.
Namespace for new ROOT classes and functions.
Definition: StringConv.hxx:21
void SetLogScan(bool on)
Set a log grid scan (default is equidistant bins) will work only if xlow > 0.
static void SetDefaultNSearch(int n)
set number of times the bracketing search in combination with is done to find a good interval Default...
const IGenFunction * fFunction
User class for performing function minimization.
virtual double FValUpper() const
Return function value at current upper bound of the minimization interval.
virtual double FValLower() const
Return function value at current lower bound of the minimization interval.
virtual const char * Name() const
Return name of minimization algorithm ("BrentMinimizer1D")
void SetFunction(const ROOT::Math::IGenFunction &f, double xlow, double xup)
Sets function to be minimized.
virtual double XLower() const
Return current lower bound of the minimization interval.
constexpr Double_t E()
Definition: TMath.h:74
double f(double x)
virtual double FValMinimum() const
Return function value at current estimate of the minimum.
Interface class for numerical methods for one-dimensional minimization.
Definition: IMinimizer1D.h:50
Namespace for new Math classes and functions.
virtual double XMinimum() const
Return current estimate of the position of the minimum.
static void SetDefaultNpx(int npx)
set number of default Npx used at construction time (when SetNpx is not called) Default value is 100 ...
virtual int Iterations() const
Return number of iteration used to find minimum.
void SetNpx(int npx)
Set the number of point used to bracket root using a grid.
virtual bool Minimize(int maxIter, double absTol=1.E-8, double relTol=1.E-10)
Find minimum position iterating until convergence specified by the absolute and relative tolerance or...
BrentMinimizer1D()
Default Constructor.
const Int_t n
Definition: legend1.C:16