ROOT  6.06/09
Reference Guide
MnParabolaFactory.cxx
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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 
11 #include "Minuit2/MnParabola.h"
13 
14 namespace ROOT {
15 
16  namespace Minuit2 {
17 
18 
19 // #include <iostream>
20 
22  const MnParabolaPoint& p2,
23  const MnParabolaPoint& p3) const {
24  // construct the parabola from 3 points p1,p2,p3
25  double x1 = p1.X();
26  double x2 = p2.X();
27  double x3 = p3.X();
28  double dx12 = x1-x2;
29  double dx13 = x1-x3;
30  double dx23 = x2-x3;
31 
32  // std::cout<<"MnParabolaFactory x1, x2, x3: "<<x1<<" "<<x2<<" "<<x3<<std::endl;
33 
34  double xm = (x1+x2+x3)/3.;
35  x1 -= xm;
36  x2 -= xm;
37  x3 -= xm;
38 
39  double y1 = p1.Y();
40  double y2 = p2.Y();
41  double y3 = p3.Y();
42  // std::cout<<"MnParabolaFactory y1, y2, y3: "<<y1<<" "<<y2<<" "<<y3<<std::endl;
43 
44  double a = y1/(dx12*dx13) - y2/(dx12*dx23) + y3/(dx13*dx23);
45  double b = -y1*(x2+x3)/(dx12*dx13) + y2*(x1+x3)/(dx12*dx23) - y3*(x1+x2)/(dx13*dx23);
46  double c = y1 - a*x1*x1 - b*x1;
47 
48  c += xm*(xm*a - b);
49  b -= 2.*xm*a;
50 
51  // std::cout<<"a,b,c= "<<a<<" "<<b<<" "<<c<<std::endl;
52  return MnParabola(a, b, c);
53 }
54 
56  double dxdy1,
57  const MnParabolaPoint& p2) const {
58  // construct the parabola from 2 points + derivative at first point dxdy1
59  double x1 = p1.X();
60  double xx1 = x1*x1;
61  double x2 = p2.X();
62  double xx2 = x2*x2;
63  double y1 = p1.Y();
64  double y12 = p1.Y() - p2.Y();
65 
66  double det = xx1-xx2 - 2.*x1*(x1-x2);
67  double a = -( y12 + (x2-x1)*dxdy1)/det;
68  double b = -( -2.*x1*y12 + (xx1-xx2)*dxdy1)/det;
69  double c = y1 - a*xx1 - b*x1;
70 
71  return MnParabola(a, b, c);
72 }
73 
74 
75  } // namespace Minuit2
76 
77 } // namespace ROOT
static double p3(double t, double a, double b, double c, double d)
Namespace for new ROOT classes and functions.
Definition: ROOT.py:1
double X() const
Accessor to the x (first) coordinate.
TArc * a
Definition: textangle.C:12
static const double x2[5]
A point of a parabola.
double Y() const
Accessor to the y (second) coordinate.
static double p2(double t, double a, double b, double c)
This class defines a parabola of the form a*x*x + b*x + c.
Definition: MnParabola.h:31
static double p1(double t, double a, double b)
static const double x1[5]
static const double x3[11]
MnParabola operator()(const MnParabolaPoint &, const MnParabolaPoint &, const MnParabolaPoint &) const