marley::RotationMatrix Class Reference

Simple rotation matrix implementation used to reorient Particle objects based on the incident neutrino direction. More...

#include <RotationMatrix.hh>

Public Member Functions
	RotationMatrix ()
	Creates a 3×3 identity matrix.
	RotationMatrix (const ThreeVector &from_vec, const ThreeVector &to_vec)
	Create a 3×3 rotation matrix that rotates the 3-vector from_vec into the 3-vector to_vec.
ThreeVector	rotate_copy (const ThreeVector &v)
	Create a rotated copy of the 3-vector v.
void	rotate_inplace (ThreeVector &v)
	Rotate a 3-vector v in place.
void	rotate_particle_inplace (HepMC3::GenParticle &p)
	Rotate the 3-momentum of a marley::Particle in place.

Static Public Member Functions
static ThreeVector	normalize (const ThreeVector &v)

Protected Attributes
ThreeThreeMatrix	matrix_
	3×3 rotation matrix

Detailed Description

Simple rotation matrix implementation used to reorient Particle objects based on the incident neutrino direction.

Definition at line 30 of file RotationMatrix.hh.

Constructor & Destructor Documentation

RotationMatrix() [1/2]

marley::RotationMatrix::RotationMatrix

(

)

Creates a 3×3 identity matrix.

Definition at line 63 of file RotationMatrix.cc.

  : matrix_{{ {{ 1., 0., 0.}}, {{ 0., 1., 0.}}, {{ 0., 0., 1.}} }}
{}

References matrix_.

RotationMatrix() [2/2]

marley::RotationMatrix::RotationMatrix	(	const ThreeVector &	from_vec,
		const ThreeVector &	to_vec )

Create a 3×3 rotation matrix that rotates the 3-vector from_vec into the 3-vector to_vec.

This function is a C++11 version of an original rotation matrix program by Möller & Hughes (see this GitHub page for details)

The vectors from_vec and to_vec do not need to be normalized, but both should be nonzero. If either vector is a null vector, then a marley::Error will be thrown.

Definition at line 122 of file RotationMatrix.cc.

{
  static constexpr ThreeVector null_three_vector = { 0., 0., 0. };
 
  if (from_vec == null_three_vector)
    throw marley::Error(std::string("Null from vector")
      + " passed to constructor of marley::RotationMatrix");
  else if (to_vec == null_three_vector)
    throw marley::Error(std::string("Null to vector")
      + " passed to constructor of marley::RotationMatrix");
 
  // The from and to vectors must be normalized to use this method, so make any
  // necessary adjustments now.
  ThreeVector from = normalize(from_vec);
  ThreeVector to = normalize(to_vec);
 
  double e = dot_product(from, to);
  double f = std::abs(e);
 
  static constexpr double EPSILON = 0.000001;
  if (f > 1.0 - EPSILON) { // "from" and "to" vectors are almost parallel
 
    // Temporary storage vectors
    ThreeVector v;
    ThreeVector u;
 
    // Find the standard unit vector x most nearly orthogonal to "from"
    ThreeVector x;
    x[0] = std::abs(from[0]);
    x[1] = std::abs(from[1]);
    x[2] = std::abs(from[2]);
 
    if (x[0] < x[1])
    {
      if (x[0] < x[2])
      {
        x[0] = 1.0; x[1] = x[2] = 0.0;
      }
      else
      {
        x[2] = 1.0; x[0] = x[1] = 0.0;
      }
    }
    else
    {
      if (x[1] < x[2])
      {
        x[1] = 1.0; x[0] = x[2] = 0.0;
      }
      else
      {
        x[2] = 1.0; x[0] = x[1] = 0.0;
      }
    }
 
    // u = x - from
    subtract(u, x, from);
 
    // v = x - to
    subtract(v, x, to);
 
    // coefficients for later use
    double c1 = 2.0 / dot_product(u, u);
    double c2 = 2.0 / dot_product(v, v);
    double c3 = c1 * c2  * dot_product(u, v);
 
    for (unsigned i = 0; i < 3; ++i) {
      for (unsigned j = 0; j < 3; ++j) {
        matrix_[i][j] =  - c1 * u[i] * u[j] - c2 * v[i] * v[j]
          + c3 * v[i] * u[j];
      }
      matrix_[i][i] += 1.0;
    }
  }
  else  // the most common case, unless "from" = "to", or "from" = -"to"
  {
    ThreeVector v;
    cross_product(v, from, to); // v = from x to
 
    // hand-optimized version (9 mults less than original)
    // optimization by Gottfried Chen
    double hvx, hvz, hvxy, hvxz, hvyz;
    double h = 1.0 / (1.0 + e);
    hvx = h * v[0];
    hvz = h * v[2];
    hvxy = hvx * v[1];
    hvxz = hvx * v[2];
    hvyz = hvz * v[1];
 
    matrix_[0][0] = e + hvx * v[0];
    matrix_[0][1] = hvxy - v[2];
    matrix_[0][2] = hvxz + v[1];
 
    matrix_[1][0] = hvxy + v[2];
    matrix_[1][1] = e + h * v[1] * v[1];
    matrix_[1][2] = hvyz - v[0];
 
    matrix_[2][0] = hvxz - v[1];
    matrix_[2][1] = hvyz + v[0];
    matrix_[2][2] = e + hvz * v[2];
  }
}

References matrix_.

Member Function Documentation

normalize()

ThreeVector marley::RotationMatrix::normalize ( const ThreeVector & v )

static

Definition at line 68 of file RotationMatrix.cc.

{
  static ThreeVector nv({0., 0., 0.});
  double norm_factor = std::sqrt(std::pow(v[0], 2) + std::pow(v[1], 2)
    + std::pow(v[2], 2));
  if (norm_factor <= 0.) throw marley::Error(std::string("Invalid vector")
    + " magnitude encountered in marley::RotationMatrix::normalize()");
  else norm_factor = 1. / norm_factor;
  nv[0] = norm_factor * v[0];
  nv[1] = norm_factor * v[1];
  nv[2] = norm_factor * v[2];
  return nv;
}

rotate_copy()

ThreeVector marley::RotationMatrix::rotate_copy

(

const ThreeVector &

v

)

Create a rotated copy of the 3-vector v.

Definition at line 83 of file RotationMatrix.cc.

{
  ThreeVector rv = {0., 0., 0.};
  for (unsigned i = 0; i < 3; ++i) rv[i] = dot_product(matrix_[i], v);
  return rv;
}

References matrix_.

rotate_inplace()

void marley::RotationMatrix::rotate_inplace

(

ThreeVector &

v

)

Rotate a 3-vector v in place.

Definition at line 91 of file RotationMatrix.cc.

{
  ThreeVector rv = {0., 0., 0.};
  for (unsigned i = 0; i < 3; ++i) rv[i] = dot_product(matrix_[i], v);
  v = rv;
}

References matrix_.

rotate_particle_inplace()

void marley::RotationMatrix::rotate_particle_inplace

(

HepMC3::GenParticle &

p

)

Rotate the 3-momentum of a marley::Particle in place.

Definition at line 99 of file RotationMatrix.cc.

{
  HepMC3::FourVector mom4 = p.momentum();
 
  ThreeVector rv = { 0., 0., 0. };
  ThreeVector three_momentum = { mom4.px(), mom4.py(), mom4.pz() };
 
  for (unsigned i = 0; i < 3; ++i)
    rv[i] = dot_product( matrix_[i], three_momentum );
 
  mom4.set_px( rv[0] );
  mom4.set_py( rv[1] );
  mom4.set_pz( rv[2] );
 
  p.set_momentum( mom4 );
}

References matrix_, HepMC3::GenParticle::momentum(), HepMC3::FourVector::px(), HepMC3::FourVector::py(), HepMC3::FourVector::pz(), HepMC3::GenParticle::set_momentum(), HepMC3::FourVector::set_px(), HepMC3::FourVector::set_py(), and HepMC3::FourVector::set_pz().

Member Data Documentation

matrix_

ThreeThreeMatrix marley::RotationMatrix::matrix_

protected

3×3 rotation matrix

Definition at line 59 of file RotationMatrix.hh.

Referenced by RotationMatrix(), RotationMatrix(), rotate_copy(), rotate_inplace(), and rotate_particle_inplace().

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

• /home/sjg/Desktop/marley/include/marley/RotationMatrix.hh
• /home/sjg/Desktop/marley/src/RotationMatrix.cc