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FCNBase.h
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1 // @(#)root/minuit2:$Id$
2 // Authors: M. Winkler, F. James, L. Moneta, A. Zsenei 2003-2005
3 
4 /**********************************************************************
5  * *
6  * Copyright (c) 2005 LCG ROOT Math team, CERN/PH-SFT *
7  * *
8  **********************************************************************/
9 
10 #ifndef ROOT_Minuit2_FCNBase
11 #define ROOT_Minuit2_FCNBase
12 
13 #include "Minuit2/MnConfig.h"
14 
15 #include <vector>
16 
17 #include "Minuit2/GenericFunction.h"
18 
19 namespace ROOT {
20 
21  namespace Minuit2 {
22 
23 
24 /**
25 
26  \defgroup Minuit Minuit2 Minimization Library
27 
28  New Object-oriented implementation of the MINUIT minimization package.
29  More information is available at the home page of the \ref Minuit2Page "Minuit2" minimization package".
30 
31  \ingroup Math
32 */
33 
34 
35 //______________________________________________________________________________
36 /**
37 
38 
39 Interface (abstract class) defining the function to be minimized, which has to be implemented by the user.
40 
41 @author Fred James and Matthias Winkler; modified by Andras Zsenei and Lorenzo Moneta
42 
43 \ingroup Minuit
44 
45  */
46 
47 class FCNBase : public GenericFunction {
48 
49 public:
50 
51 
52  virtual ~FCNBase() {}
53 
54 
55 
56  /**
57 
58  The meaning of the vector of parameters is of course defined by the user,
59  who uses the values of those parameters to calculate their function Value.
60  The order and the position of these parameters is strictly the one specified
61  by the user when supplying the starting values for minimization. The starting
62  values must be specified by the user, either via an std::vector<double> or the
63  MnUserParameters supplied as input to the MINUIT minimizers such as
64  VariableMetricMinimizer or MnMigrad. Later values are determined by MINUIT
65  as it searches for the Minimum or performs whatever analysis is requested by
66  the user.
67 
68  @param par function parameters as defined by the user.
69 
70  @return the Value of the function.
71 
72  @see MnUserParameters
73  @see VariableMetricMinimizer
74  @see MnMigrad
75 
76  */
77 
78  virtual double operator()(const std::vector<double>& x) const = 0;
79 
80 
81  /**
82 
83  Error definition of the function. MINUIT defines Parameter errors as the
84  change in Parameter Value required to change the function Value by up. Normally,
85  for chisquared fits it is 1, and for negative log likelihood, its Value is 0.5.
86  If the user wants instead the 2-sigma errors for chisquared fits, it becomes 4,
87  as Chi2(x+n*sigma) = Chi2(x) + n*n.
88 
89  Comment a little bit better with links!!!!!!!!!!!!!!!!!
90 
91  */
92 
93  virtual double ErrorDef() const {return Up();}
94 
95 
96  /**
97 
98  Error definition of the function. MINUIT defines Parameter errors as the
99  change in Parameter Value required to change the function Value by up. Normally,
100  for chisquared fits it is 1, and for negative log likelihood, its Value is 0.5.
101  If the user wants instead the 2-sigma errors for chisquared fits, it becomes 4,
102  as Chi2(x+n*sigma) = Chi2(x) + n*n.
103 
104  \todo Comment a little bit better with links!!!!!!!!!!!!!!!!! Idem for ErrorDef()
105 
106  */
107 
108  virtual double Up() const = 0;
109 
110  /**
111  add interface to set dynamically a new error definition
112  Re-implement this function if needed.
113  */
114  virtual void SetErrorDef(double ) {};
115 
116 };
117 
118  } // namespace Minuit2
119 
120 } // namespace ROOT
121 
122 #endif // ROOT_Minuit2_FCNBase