SphericityEigenvalues Class Reference

Class to calculate the Sphericity tensor eigenvalues and eigenvectors starting from an array of 3-momenta The tensor itself is not stored, only its eigenvalues and eigenvectors are. More...

#include <SphericityEigenvalues.h>

Public Member Functions
	SphericityEigenvalues (const std::vector< ROOT::Math::XYZVector > &momenta)
	Constructor with an array of 3-momenta.
	~SphericityEigenvalues ()
	Default destructor.
void	setMomenta (const std::vector< ROOT::Math::XYZVector > &momenta)
	Sets the list of momenta to be used in the calculation overwriting the previous values.
void	calculateEigenvalues ()
	Calculates eigenvalues and eigenvectors.
double	getEigenvalue (short i) const
	Returns the i-th Eigenvalue.
ROOT::Math::XYZVector	getEigenvector (short i) const
	Returns the i-th Eigenvector.

Private Attributes
double	m_lambda [3] = {0.}
	The eigenvalues.
ROOT::Math::XYZVector	m_eVector [3]
	The eigenvectors.
std::vector< ROOT::Math::XYZVector >	m_momenta
	The particles' momenta.

Detailed Description

Class to calculate the Sphericity tensor eigenvalues and eigenvectors starting from an array of 3-momenta The tensor itself is not stored, only its eigenvalues and eigenvectors are.

Definition at line 24 of file SphericityEigenvalues.h.

Constructor & Destructor Documentation

SphericityEigenvalues()

SphericityEigenvalues ( const std::vector< ROOT::Math::XYZVector > &  momenta )

inlineexplicit

Constructor with an array of 3-momenta.

Definition at line 30 of file SphericityEigenvalues.h.

    {
      m_momenta.clear();
      m_momenta = momenta;
    }

~SphericityEigenvalues()

~SphericityEigenvalues ( )

inline

Default destructor.

Definition at line 39 of file SphericityEigenvalues.h.

{};

Member Function Documentation

calculateEigenvalues()

void calculateEigenvalues

(

)

Calculates eigenvalues and eigenvectors.

Definition at line 19 of file SphericityEigenvalues.cc.

{
  Eigen::Matrix3f sphericityTensor;
 
  // elements of the matrix, in rows
  // n = r*3+c, using all 0-based indexes:
  // 00 = 0
  // 01 = 1
  // 10 = 3
  // 12 = 5
  // 22 = 8
  // etc...
  // diagonal = 0, 4, 8
  double elements[9] = {0.};
 
  // normalization
  double norm = 0;
 
 
  if (m_momenta.size() < 2) {
    B2WARNING("The particle list has less than 2 elements. The sphericity matrix will not be calculated");
    return;
  }
 
  for (const auto& p : m_momenta) {
    elements[0] += p.X() * p.X(); // diag
    elements[1] += p.X() * p.Y();
    elements[2] += p.X() * p.Z();
 
    elements[3] += p.Y() * p.X();
    elements[4] += p.Y() * p.Y(); // diag
    elements[5] += p.Y() * p.Z();
 
    elements[6] += p.Z() * p.X();
    elements[7] += p.Z() * p.Y();
    elements[8] += p.Z() * p.Z(); // diag
    norm += p.Mag2();
  }
 
  for (short i = 0; i < 3; i++) {
    for (short j = 0; j < 3; j++) {
      sphericityTensor(i, j) = elements[i * 3 + j] / norm;
    }
  }
 
  auto eigenVals = sphericityTensor.eigenvalues();
  Eigen::ComplexEigenSolver<Eigen::MatrixXcf> ces(sphericityTensor);
 
  // unfortunately Eigen does not provide the eigenvalues in
  // any specific order, so we have to sort them and keep also the correct eigenvector-eigenvalue
  // associations...
 
  short order[3] = {0, 1, 2};
 
  std::vector<float> tmpLambda;
  for (short i = 0; i < 3; i++) {
    tmpLambda.push_back(eigenVals[i].real());
  }
 
  // position of the largest Eigenvalue
  order[0] =  std::distance(tmpLambda.begin(), std::max_element(tmpLambda.begin(), tmpLambda.end()));
  // position of the smallest Eigenvalue
  order[2] =  std::distance(tmpLambda.begin(), std::min_element(tmpLambda.begin(), tmpLambda.end()));
  // position of the middle eigenvalue
  order[1] = (short)(3.1 - (order[0] + order[2]));
 
  for (short i = 0; i < 3; i++) {
    short n = order[i];
    m_lambda[i] = eigenVals[n].real();
    auto eigenVector =  ces.eigenvectors().col(n);
    m_eVector[i].SetX(eigenVector[0].real());
    m_eVector[i].SetY(eigenVector[1].real());
    m_eVector[i].SetZ(eigenVector[2].real());
  }
 
  return;
}

getEigenvalue()

double getEigenvalue ( short  i ) const

inline

Returns the i-th Eigenvalue.

Definition at line 62 of file SphericityEigenvalues.h.

    {
      return (i < 0 || i > 3) ? 0. : m_lambda[i];
    }

getEigenvector()

ROOT::Math::XYZVector getEigenvector ( short  i ) const

inline

Returns the i-th Eigenvector.

Definition at line 70 of file SphericityEigenvalues.h.

    {
      ROOT::Math::XYZVector nullVector(0., 0., 0.);
      return (i < 0 || i > 3) ? nullVector : m_eVector[i];
    }

setMomenta()

void setMomenta ( const std::vector< ROOT::Math::XYZVector > &  momenta )

inline

Sets the list of momenta to be used in the calculation overwriting the previous values.

Definition at line 46 of file SphericityEigenvalues.h.

    {
      m_momenta.clear();
      m_momenta = momenta;
    }

Member Data Documentation

m_eVector

ROOT::Math::XYZVector m_eVector[3]

private

The eigenvectors.

Definition at line 79 of file SphericityEigenvalues.h.

m_lambda

double m_lambda[3] = {0.}

private

The eigenvalues.

Definition at line 78 of file SphericityEigenvalues.h.

m_momenta

std::vector<ROOT::Math::XYZVector> m_momenta

private

The particles' momenta.

Definition at line 80 of file SphericityEigenvalues.h.

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The documentation for this class was generated from the following files:

• analysis/ContinuumSuppression/include/SphericityEigenvalues.h
• analysis/ContinuumSuppression/src/SphericityEigenvalues.cc