 ROOT   Reference Guide MnParabola.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_MnParabola
11#define ROOT_Minuit2_MnParabola
12
13#include <math.h>
14
15namespace ROOT {
16
17 namespace Minuit2 {
18
19
20/**
21
22This class defines a parabola of the form a*x*x + b*x + c
23
25and Lorenzo Moneta
26
27@ingroup Minuit
28
29 */
30
32
33public:
34
35
36 /**
37
38 Constructor that initializes the parabola with its three parameters.
39
40 @param a the coefficient of the quadratic term
41 @param b the coefficient of the linear term
42 @param c the constant
43
44 */
45
46 MnParabola(double a, double b, double c) : fA(a), fB(b), fC(c) {}
47
48
50
51
52 /**
53
54 Evaluates the parabola a the point x.
55
56 @param x the coordinate where the parabola needs to be evaluated.
57
58 @return the y coordinate of the parabola corresponding to x.
59
60 */
61
62 double Y(double x) const {return (fA*x*x + fB*x +fC);}
63
64
65 /**
66
67 Calculates the bigger of the two x values corresponding to the
68 given y Value.
69
70 <p>
71
72 ???????!!!!!!!!! And when there is none?? it looks like it will
73 crash?? what is sqrt (-1.0) ?
74
75 @param y the y Value for which the x Value is to be calculated.
76
77 @return the bigger one of the two corresponding values.
78
79 */
80
81 // ok, at first glance it does not look like the formula for the quadratic
82 // equation, but it is! ;-)
83 double X_pos(double y) const {return (sqrt(y/fA + Min()*Min() - fC/fA) + Min());}
84 // maybe it is worth to check the performance improvement with the below formula??
85 // double X_pos(double y) const {return (sqrt(y/fA + fB*fB/(4.*fA*fA) - fC/fA) - fB/(2.*fA));}
86
87
88
89 /**
90
91 Calculates the smaller of the two x values corresponding to the
92 given y Value.
93
94 <p>
95
96 ???????!!!!!!!!! And when there is none?? it looks like it will
97 crash?? what is sqrt (-1.0) ?
98
99 @param y the y Value for which the x Value is to be calculated.
100
101 @return the smaller one of the two corresponding values.
102
103 */
104
105 double X_neg(double y) const {return (-sqrt(y/fA + Min()*Min() - fC/fA) + Min());}
106
107
108 /**
109
110 Calculates the x coordinate of the Minimum of the parabola.
111
112 @return x coordinate of the Minimum.
113
114 */
115
116 double Min() const {return -fB/(2.*fA);}
117
118
119 /**
120
121 Calculates the y coordinate of the Minimum of the parabola.
122
123 @return y coordinate of the Minimum.
124
125 */
126
127 double YMin() const {return (-fB*fB/(4.*fA) + fC);}
128
129
130 /**
131
132 Accessor to the coefficient of the quadratic term.
133
134 @return the coefficient of the quadratic term.
135
136 */
137
138 double A() const {return fA;}
139
140
141 /**
142
143 Accessor to the coefficient of the linear term.
144
145 @return the coefficient of the linear term.
146
147 */
148
149 double B() const {return fB;}
150
151
152 /**
153
154 Accessor to the coefficient of the constant term.
155
156 @return the coefficient of the constant term.
157
158 */
159
160 double C() const {return fC;}
161
162private:
163
164 double fA;
165 double fB;
166 double fC;
167};
168
169 } // namespace Minuit2
170
171} // namespace ROOT
172
173#endif // ROOT_Minuit2_MnParabola
#define b(i)
Definition: RSha256.hxx:100
#define c(i)
Definition: RSha256.hxx:101
double sqrt(double)
This class defines a parabola of the form a*x*x + b*x + c.
Definition: MnParabola.h:31
double X_neg(double y) const
Calculates the smaller of the two x values corresponding to the given y Value.
Definition: MnParabola.h:105
double X_pos(double y) const
Calculates the bigger of the two x values corresponding to the given y Value.
Definition: MnParabola.h:83
double YMin() const
Calculates the y coordinate of the Minimum of the parabola.
Definition: MnParabola.h:127
double B() const
Accessor to the coefficient of the linear term.
Definition: MnParabola.h:149
double C() const
Accessor to the coefficient of the constant term.
Definition: MnParabola.h:160
double Min() const
Calculates the x coordinate of the Minimum of the parabola.
Definition: MnParabola.h:116
double A() const
Accessor to the coefficient of the quadratic term.
Definition: MnParabola.h:138
MnParabola(double a, double b, double c)
Constructor that initializes the parabola with its three parameters.
Definition: MnParabola.h:46
double Y(double x) const
Evaluates the parabola a the point x.
Definition: MnParabola.h:62
Double_t y[n]
Definition: legend1.C:17
Double_t x[n]
Definition: legend1.C:17
VSD Structures.
Definition: StringConv.hxx:21
auto * a
Definition: textangle.C:12