Acts::GaussianTrackDensity Class Reference

Class to model tracks as 2D density functions based on their d0 and z0 perigee parameters (mean value) and covariance matrices (determining the width of the function). More...

#include <Acts/Vertexing/GaussianTrackDensity.hpp>

Classes
struct	Config
	The Config struct. More...
struct	State
	The State struct. More...
struct	TrackEntry
	Struct to store information for a single track. More...

Public Member Functions
	GaussianTrackDensity (const Config &cfg)
	Constructor with config.
Result< std::optional< double > >	globalMaximum (State &state, const std::vector< InputTrack > &trackList) const
	Calculates the z position of the global maximum.
Result< std::optional< std::pair< double, double > > >	globalMaximumWithWidth (State &state, const std::vector< InputTrack > &trackList) const
	Calculates z position of global maximum with Gaussian width for density function.

Detailed Description

Class to model tracks as 2D density functions based on their d0 and z0 perigee parameters (mean value) and covariance matrices (determining the width of the function).

Constructor & Destructor Documentation

GaussianTrackDensity()

Acts::GaussianTrackDensity::GaussianTrackDensity ( const Config & cfg )

explicit

Constructor with config.

Parameters

cfg	The configuration parameters

Member Function Documentation

globalMaximum()

Result< std::optional< double > > Acts::GaussianTrackDensity::globalMaximum	(	State &	state,
		const std::vector< InputTrack > &	trackList ) const

Calculates the z position of the global maximum.

Parameters

state	The track density state
trackList	All input tracks

Returns

z position of the global maximum

globalMaximumWithWidth()

Result< std::optional< std::pair< double, double > > > Acts::GaussianTrackDensity::globalMaximumWithWidth	(	State &	state,
		const std::vector< InputTrack > &	trackList ) const

Calculates z position of global maximum with Gaussian width for density function.

Strategy: The global maximum must be somewhere near a track. Since we can calculate the first and second derivatives, at each point we can determine a) whether the function is curved up (minimum) or down (maximum) b) the distance to nearest maximum, assuming either Newton (parabolic) or Gaussian local behavior. For each track where the second derivative is negative, find step to nearest maximum, take that step and then do one final refinement. The largest density encountered in this procedure (after checking all tracks) is considered the maximum.

Parameters

state	The track density state
trackList	All input tracks

Returns

Pair of position of global maximum and Gaussian width