marley::ProjectileDirectionRotator Class Reference

If needed, rotates the coordinate system of a GenEvent so that the projectile 3-momentum lies along a desired direction. More...

#include <ProjectileDirectionRotator.hh>

Inheritance diagram for marley::ProjectileDirectionRotator:

Public Member Functions
	ProjectileDirectionRotator (const ThreeVector &dir={0., 0., 1.})
virtual void	process_event (HepMC3::GenEvent &ev, marley::Generator &gen) override
	Rotates all 3-momenta in the input event so that the projectile 3-momentum lies along dir_vec_ in the new coordinate system.
const ThreeVector &	projectile_direction () const
ThreeVector	sample_isotropic_direction (marley::Generator &gen) const
void	set_projectile_direction (const ThreeVector &dir)
void	set_randomize_directions (bool do_sampling)

Protected Member Functions
void	rotate_event (HepMC3::GenEvent &ev)
	Helper function that does the coordinate system rotation.

Protected Attributes
ThreeVector	dir_vec_ = {{ 0., 0., 1. }}
	3-vector that points in the desired direction of the projectile
ThreeVector	last_pdir_ = {{ 0., 0., 1. }}
	Stores the direction 3-vector for the last projectile that triggered a recalculation of the rotation matrix.
bool	randomize_projectile_direction_ = false
	Flag that indicates whether the (rotated) projectile direction should be sampled isotropically for each event (true) or kept fixed across all events (false)
marley::RotationMatrix	rot_matrix_
	RotationMatrix used to rotate the coordinate system of the input GenEvent.

Detailed Description

If needed, rotates the coordinate system of a GenEvent so that the projectile 3-momentum lies along a desired direction.

Definition at line 27 of file ProjectileDirectionRotator.hh.

Constructor & Destructor Documentation

ProjectileDirectionRotator()

marley::ProjectileDirectionRotator::ProjectileDirectionRotator

(

const ThreeVector &

dir = {0., 0., 1.}

)

Parameters

dir	A 3-vector pointing in the desired direction of the projectile in the rotated coordinate system

Definition at line 28 of file ProjectileDirectionRotator.cc.

                                   : EventProcessor(),
  dir_vec_( dir )
{
  constexpr ThreeVector null_three_vector = { 0., 0., 0. };
  if ( dir_vec_ == null_three_vector ) throw marley::Error( "Null 3-vector"
    " passed to constructor of marley::ProjectileDirectionRotator" );
 
  dir_vec_ = marley::RotationMatrix::normalize( dir_vec_ );
}

References dir_vec_.

Member Function Documentation

process_event()

void marley::ProjectileDirectionRotator::process_event ( HepMC3::GenEvent & ev, marley::Generator & gen )

overridevirtual

Rotates all 3-momenta in the input event so that the projectile 3-momentum lies along dir_vec_ in the new coordinate system.

Implements marley::EventProcessor.

Definition at line 39 of file ProjectileDirectionRotator.cc.

{
  // First check that the projectile 3-momentum is not a null vector.
  // If it is, don't bother to rotate coordinates. Also don't bother if
  // (somehow) the magnitude of the projectile momentum is negative.
  const auto projectile = marley_hepmc3::get_projectile( ev );
  HepMC3::FourVector mom4 = projectile->momentum();
  double pmom = mom4.p3mod();
  if ( pmom <= 0. ) return;
 
  ThreeVector pdir = { mom4.px() / pmom, mom4.py() / pmom, mom4.pz() / pmom };
 
  // If random projectile directions have been requested, then sample
  // a new one isotropically for this event
  if ( randomize_projectile_direction_ ) {
    ThreeVector random_dir = sample_isotropic_direction( gen );
    this->set_projectile_direction( random_dir );
  }
 
  // If the (unrotated) projectile direction from the event exactly matches the
  // desired direction, then we can skip the coordinate rotation.
  if ( pdir == dir_vec_ ) return;
 
  // If the (unrotated) projectile direction from the event differs from
  // the last one that was processed, then we need to recompute the
  // rotation matrix. Do so and save the unrotated projectile direction
  // to repeat this check next time.
  if ( pdir != last_pdir_ ) {
    last_pdir_ = pdir;
    rot_matrix_ = marley::RotationMatrix( pdir, dir_vec_ );
  }
 
  // Do the actual rotation of the Particle 3-momenta in the event
  this->rotate_event( ev );
}

References dir_vec_, last_pdir_, HepMC3::FourVector::p3mod(), HepMC3::FourVector::px(), HepMC3::FourVector::py(), HepMC3::FourVector::pz(), randomize_projectile_direction_, rot_matrix_, and rotate_event().

Referenced by marley::Generator::create_event().

projectile_direction()

const ThreeVector & marley::ProjectileDirectionRotator::projectile_direction ( ) const

inline

Definition at line 45 of file ProjectileDirectionRotator.hh.

        { return dir_vec_; }

rotate_event()

void marley::ProjectileDirectionRotator::rotate_event ( HepMC3::GenEvent & ev )

protected

Helper function that does the coordinate system rotation.

Parameters

[in,out]

ev

GenEvent whose Particle 3-vectors will be rotated

Definition at line 76 of file ProjectileDirectionRotator.cc.

                                                                        {
 
  for ( auto& p : ev.particles() ) {
    rot_matrix_.rotate_particle_inplace( *p );
  }
 
}

References HepMC3::GenEvent::particles(), and rot_matrix_.

Referenced by process_event().

sample_isotropic_direction()

marley::ProjectileDirectionRotator::ThreeVector marley::ProjectileDirectionRotator::sample_isotropic_direction

(

marley::Generator &

gen

)

const

Definition at line 85 of file ProjectileDirectionRotator.cc.

{
  // Sample a polar cosine on the interval [-1, 1]
  double cos_theta = gen.uniform_random_double( -1., 1., true );
 
  // Sample an azimuthal angle on the interval [0, 2*pi)
  double phi = gen.uniform_random_double( 0., marley_utils::two_pi, false );
 
  // Compute direction unit vector components
  double sin_theta = marley_utils::real_sqrt( 1. - std::pow(cos_theta, 2) );
  double ux = sin_theta * std::cos( phi );
  double uy = sin_theta * std::sin( phi );
  double uz = cos_theta;
 
  ThreeVector direction = { ux, uy, uz };
  return direction;
}

set_projectile_direction()

void marley::ProjectileDirectionRotator::set_projectile_direction ( const ThreeVector & dir )

inline

Definition at line 48 of file ProjectileDirectionRotator.hh.

                                                                     {
        dir_vec_ = marley::RotationMatrix::normalize( dir );
        last_pdir_ = dir_vec_;
      }

set_randomize_directions()

void marley::ProjectileDirectionRotator::set_randomize_directions

(

bool

do_sampling

)

Definition at line 104 of file ProjectileDirectionRotator.cc.

{
  randomize_projectile_direction_ = do_sampling;
}

Member Data Documentation

dir_vec_

ThreeVector marley::ProjectileDirectionRotator::dir_vec_ = {{ 0., 0., 1. }}

protected

3-vector that points in the desired direction of the projectile

Definition at line 61 of file ProjectileDirectionRotator.hh.

{{ 0., 0., 1. }};

Referenced by ProjectileDirectionRotator(), and process_event().

last_pdir_

ThreeVector marley::ProjectileDirectionRotator::last_pdir_ = {{ 0., 0., 1. }}

protected

Stores the direction 3-vector for the last projectile that triggered a recalculation of the rotation matrix.

Using this information avoids unnecessary recalculations

Definition at line 66 of file ProjectileDirectionRotator.hh.

{{ 0., 0., 1. }};

Referenced by process_event().

randomize_projectile_direction_

bool marley::ProjectileDirectionRotator::randomize_projectile_direction_ = false

protected

Flag that indicates whether the (rotated) projectile direction should be sampled isotropically for each event (true) or kept fixed across all events (false)

Definition at line 79 of file ProjectileDirectionRotator.hh.

Referenced by process_event().

rot_matrix_

marley::RotationMatrix marley::ProjectileDirectionRotator::rot_matrix_

protected

RotationMatrix used to rotate the coordinate system of the input GenEvent.

Definition at line 70 of file ProjectileDirectionRotator.hh.

Referenced by process_event(), and rotate_event().

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

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