DiscreteWavelengthDistribution Class Reference

#include <DiscreteWavelengthDistribution.hpp>

Inheritance diagram for DiscreteWavelengthDistribution:

Public Member Functions
double	generateWavelength () const override
double	probability (double wavelength) const override
DisjointWavelengthGrid *	wavelengthGrid () const
Public Member Functions inherited from SimulationItem
template<class T>
T *	find (bool setup=true) const
template<class T>
T *	interface (int levels=-999999, bool setup=true) const
virtual string	itemName () const
void	setup ()
string	typeAndName () const
Public Member Functions inherited from Item
	Item (const Item &)=delete
virtual	~Item ()
void	addChild (Item *child)
const vector< Item * > &	children () const
virtual void	clearItemListProperty (const PropertyDef *property)
void	destroyChild (Item *child)
virtual bool	getBoolProperty (const PropertyDef *property) const
virtual vector< double >	getDoubleListProperty (const PropertyDef *property) const
virtual double	getDoubleProperty (const PropertyDef *property) const
virtual string	getEnumProperty (const PropertyDef *property) const
virtual int	getIntProperty (const PropertyDef *property) const
virtual vector< Item * >	getItemListProperty (const PropertyDef *property) const
virtual Item *	getItemProperty (const PropertyDef *property) const
virtual string	getStringProperty (const PropertyDef *property) const
int	getUtilityProperty (string name) const
virtual void	insertIntoItemListProperty (const PropertyDef *property, int index, Item *item)
Item &	operator= (const Item &)=delete
Item *	parent () const
virtual void	removeFromItemListProperty (const PropertyDef *property, int index)
virtual void	setBoolProperty (const PropertyDef *property, bool value)
virtual void	setDoubleListProperty (const PropertyDef *property, vector< double > value)
virtual void	setDoubleProperty (const PropertyDef *property, double value)
virtual void	setEnumProperty (const PropertyDef *property, string value)
virtual void	setIntProperty (const PropertyDef *property, int value)
virtual void	setItemProperty (const PropertyDef *property, Item *item)
virtual void	setStringProperty (const PropertyDef *property, string value)
void	setUtilityProperty (string name, int value)
virtual string	type () const

Protected Member Functions
	DiscreteWavelengthDistribution ()
void	setupSelfAfter () override
Protected Member Functions inherited from WavelengthDistribution
	WavelengthDistribution ()
Random *	random () const
void	setupSelfBefore () override
Protected Member Functions inherited from SimulationItem
	SimulationItem ()
virtual bool	offersInterface (const std::type_info &interfaceTypeInfo) const
Protected Member Functions inherited from Item
	Item ()

Private Types
using	BaseType
using	ItemType

Private Attributes
int	_beginWavelengthIndex
int	_endWavelengthIndex
int	_numWavelengths
DisjointWavelengthGrid *	_wavelengthGrid

Friends
class	ItemRegistry

Detailed Description

DiscreteWavelengthDistribution is a specialty class for representing discrete wavelength probability distributions derived from a wavelength grid that can be configured by the user. This class is useful for mimicking codes that emit photon packets at discrete wavelengths rather than across a continuous range, perhaps to compare results in the context of a benchmark. One has to take great care when using this class in a simulation configuration, as indicated in more detail below.

When a DiscreteWavelengthDistribution instance is used as the wavelength bias distribution for a source with a composite bias factor of one, the source will emit photon packets only at the characteristic wavelengths of the configured grid, and the photon packets will be distributed with equal probability among those wavelengths. More precisely, the DiscreteWavelengthDistribution instance uses only the characteristic wavelengths of the configured grid that fall inside the wavelength range of the associated source (obtained through the SourceWavelengthRangeInterface). If none of the characteristic wavelengths fall inside the source range, a fatal error is issued.

When sending photon packets at a particular grid of discrete wavelengths, it makes little sense to configure wavelength grids with different bins for detecting photon packets in other areas of the simulation. Doing so might cause unexpected results. For example, some bins might receive no photon packets at all and thus incorrectly report zero influx. It is therefore best to configure the same wavelength grid throughout the simulation.

To configure a simulation that uses discrete wavelengths, follow these guidelines:

• Choose a wavelength grid with adjacent bins (i.e. representing a continuous range), such as a LogWavelengthGrid or a FileWavelengthGrid with relativeHalfWidth set to zero.
• Configure all primary and secondary sources (including, e.g. dust emission) with a wavelength bias factor of one, and a wavelength bias distribution of type DiscreteWavelengthDistribution using the chosen wavelength grid.
• Explicitly configure all wavelength grids in the simulation to be the same chosen wavelength grid. This includes the radiation field wavelength grid, the dust emission wavelength grid, and the wavelength grids for all instruments and probes.
• Avoid using kinematics in the simulation. Small Doppler shifts from the emitted discrete wavelengths will stay within the same wavelength bin anyway. Larger shifts will cause photon packets to move between wavelength bins in a discontinuous way.

Constructor & Destructor Documentation

DiscreteWavelengthDistribution()

DiscreteWavelengthDistribution::DiscreteWavelengthDistribution ( )

inlineprotected

Default constructor for concrete Item subclass DiscreteWavelengthDistribution: "a discrete wavelength probability distribution derived from a wavelength grid".

Member Function Documentation

generateWavelength()

double DiscreteWavelengthDistribution::generateWavelength ( ) const

overridevirtual

This function draws a random wavelength from the wavelength distribution. For this class, it generates one of the (in-range) characteristic wavelengths of the configured grid, with equal probability. In other words, it implements a Dirac-delta function within each of the (in-range) bins of the configured wavelength grid.

Implements WavelengthDistribution.

probability()

double DiscreteWavelengthDistribution::probability ( double wavelength ) const

overridevirtual

This function returns the probability of the distribution at the given wavelength. It acts as if the wavelengths generated by the generateWavelength() function were spread out over each bin (rather than being concentrated into a single wavelength). The returned probability is zero for wavelengths outside of the (in-range) bins of the configured wavelength grid. For a wavelength that falls inside bin \(\ell\), the returned probability is given by \( p_\ell = 1 / (\Delta\lambda_\ell \, N_\text{bins}) \), where \(\Delta\lambda_\ell\) is the width of the bin and \(N_\text{bins}\) is the number of (in-range) bins. This value is inversely proportional to the bin width, reflecting the equal distribution of generated wavelengths over the bins, and satisfies the normalization condition \(\sum_\ell p_\ell = 1\).

Implements WavelengthDistribution.

setupSelfAfter()

void DiscreteWavelengthDistribution::setupSelfAfter ( )

overrideprotectedvirtual

This function determines the grid wavelengths that fall inside the source range.

Reimplemented from SimulationItem.

wavelengthGrid()

DisjointWavelengthGrid * DiscreteWavelengthDistribution::wavelengthGrid ( ) const

inline

This function returns the value of the discoverable item property wavelengthGrid: "the wavelength grid defining the discrete distribution".

The default value for this property is given by the conditional value expression "FileWavelengthGrid".

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

• DiscreteWavelengthDistribution.hpp