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