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casa::SpectralIndex Class Reference

Models the spectral variation with a spectral index. More...

#include <SpectralIndex.h>

Inheritance diagram for casa::SpectralIndex:
casa::SpectralModel casa::RecordTransformable

List of all members.

Public Member Functions

 SpectralIndex ()
 The default SpectralIndex has a reference frequency of 1 GHz in the LSR frame and a spectral index of zero.
 SpectralIndex (const MFrequency &refFreq, Double exponent=0.0)
 Construct a SpectralIndex with specified reference frequency and exponent.
 SpectralIndex (const SpectralIndex &other)
 The copy constructor uses copy semantics.
virtual ~SpectralIndex ()
 The destructor does nothing special.
SpectralIndexoperator= (const SpectralIndex &other)
 The assignment operator uses copy semantics.
virtual
ComponentType::SpectralShape 
type () const
 return the actual spectral type ie., ComponentType::SPECTRAL_INDEX
const Doubleindex () const
 set/get the spectral index.
void setIndex (const Double &newIndex)
virtual Double sample (const MFrequency &centerFrequency) const
 Return the scaling factor that indicates what proportion of the flux is at the specified frequency.
virtual void sample (Vector< Double > &scale, const Vector< MFrequency::MVType > &frequencies, const MFrequency::Ref &refFrame) const
 Same as the previous function except that many frequencies can be sampled at once.
virtual SpectralModelclone () const
 Return a pointer to a copy of this object upcast to a SpectralModel object.
virtual uInt nParameters () const
 return the number of parameters.
virtual void setParameters (const Vector< Double > &newSpectralParms)
virtual Vector< Doubleparameters () const
virtual void setErrors (const Vector< Double > &newSpectralErrs)
virtual Vector< Doubleerrors () const
virtual Bool fromRecord (String &errorMessage, const RecordInterface &record)
 These functions convert between a Record and a SpectralIndex.
virtual Bool toRecord (String &errorMessage, RecordInterface &record) const
 Convert the class to an Record representation.
virtual Bool convertUnit (String &errorMessage, const RecordInterface &record)
 Convert the parameters of the spectral index object to the specified units.
virtual Bool ok () const
 Function which checks the internal data of this class for consistant values.

Private Attributes

Double itsIndex
Double itsError

Detailed Description

Models the spectral variation with a spectral index.

Intended use:

Public interface

 <h3>Review Status</h3><dl><dt>Date Reviewed:<dd>yyyy/mm/dd<dt>Test programs:<dd>tSpectralIndex<dt>Demo programs:<dd>dSpectralModel</dl> 

Prerequisite

Synopsis

This class models the spectral variation of a component with a spectral index.

This class like the other spectral models becomes more useful when used through the SkyComponent class, which incorporates the flux and spatial variation of the emission, or through the ComponentList class, which handles groups of SkyComponent objects.

A spectral index is the exponent in a power law model for the variation flux with frequency. It is mathematically is defined as:

     (nu / nu_0)^alpha

Where:

nu_0
is the reference frequency
alpha
is the spectral index
nu
is the user specified frequency

As with all classes derived from SpectralModel the basic operation of this class is to model the flux as a function of frequency. This class does not know what the flux is at the reference frequency. Instead the sample functions return factors that are used to scale the flux and calculate the amount of flux at a specified frequency.

Besides the reference frequency this class has one parameter; the spectral index. This parameter can be set & queried using the general purpose parameters functions or the class specific index functions.

This class also contains functions (toRecord & fromRecord) which perform the conversion between Records and SpectralIndex objects. These functions define how a SpectralIndex object is represented in glish. The format of the record that is generated and accepted by these functions is:

    c := [type = 'spectral index',
          frequency = [type = 'frequency',
                       refer = 'lsr',
                       m0 = [value = 1, unit = 'GHz']
                      ],
          index = 0.7
         ]

The frequency field contains a record representation of a frequency measure and its format is defined in the Measures module. Its refer field defines the reference frame for the direction and the m0 field defines the value of the reference frequency. The parsing of the type field is case insensitive. The index field contains the spectral index.

Example

These examples are coded in the tSpectralModel.h file.

Example 1:

In this example a SpectralIndex object is created and used to calculate the flux at a number of frequencies.

     SpectralIndex siModel;
     siModel.setRefFrequency(MFrequency(Quantity(1.0, "GHz")));
     siModel.setIndex(1.0, Stokes::I);  
     siModel.setIndex(0.5, Stokes::Q);  
     siModel.setIndex(0.5, Stokes::U);  
     siModel.setIndex(-1.0, Stokes::V);
     const Flux<Double> LBandFlux(1.0, 1.0, 1.0, 1.0);
     const MVFrequency step(Quantity(100.0, "MHz"));
     MVFrequency sampleFreq = siModel.refFrequency().getValue();
     Flux<Double> sampleFlux;
     cout << "Frequency\t I-Flux\t Q-Flux\t U-Flux\t V-Flux\n";
     for (uInt i = 0; i < 11; i++) {
       sampleFlux = LBandFlux.copy();
       sampleFlux.convertPol(ComponentType::LINEAR);
       sampleFlux.convertUnit(Unit("WU"));
       siModel.sample(sampleFlux,
                     MFrequency(sampleFreq, siModel.refFrequency().getRef()));
       cout << setprecision(3) << sampleFreq.get("GHz")
            << "\t\t " << sampleFlux.value(0u).re
            << "\t " << sampleFlux.value(1u).re
            << "\t " << sampleFlux.value(2u).re
            << "\t " << sampleFlux.value(3u).re
            << " " << sampleFlux.unit().getName() << endl;
       sampleFreq += step;
     }

Motivation

A Spectral Index frequency variation is the most widely used model in radio astronomy. In particular the NFRA package 'newstar' uses it extensively.

To Do

Definition at line 156 of file SpectralIndex.h.


Constructor & Destructor Documentation

The default SpectralIndex has a reference frequency of 1 GHz in the LSR frame and a spectral index of zero.

As such it is no different from the ConstantSpectrum class (except slower).

casa::SpectralIndex::SpectralIndex ( const MFrequency refFreq,
Double  exponent = 0.0 
)

Construct a SpectralIndex with specified reference frequency and exponent.

The copy constructor uses copy semantics.

virtual casa::SpectralIndex::~SpectralIndex ( ) [virtual]

The destructor does nothing special.


Member Function Documentation

virtual SpectralModel* casa::SpectralIndex::clone ( ) const [virtual]

Return a pointer to a copy of this object upcast to a SpectralModel object.

The class that uses this function is responsible for deleting the pointer. This is used to implement a virtual copy constructor.

Implements casa::SpectralModel.

virtual Bool casa::SpectralIndex::convertUnit ( String errorMessage,
const RecordInterface record 
) [virtual]

Convert the parameters of the spectral index object to the specified units.

Only one field of the supplied record is used, namely 'index'. This field is optional as the spectral index is a unitless quantity. If the index field is specified it must have the empty string as its value. This function always returns True unless the index field is specified and does not contain an empty string.

Implements casa::SpectralModel.

virtual Vector<Double> casa::SpectralIndex::errors ( ) const [virtual]

Implements casa::SpectralModel.

virtual Bool casa::SpectralIndex::fromRecord ( String errorMessage,
const RecordInterface record 
) [virtual]

These functions convert between a Record and a SpectralIndex.

These functions define how a SpectralIndex object is represented in glish and this is detailed in the synopsis above. These functions return False if the record is malformed and append an error message to the supplied string giving the reason.

Implements casa::SpectralModel.

set/get the spectral index.

virtual uInt casa::SpectralIndex::nParameters ( ) const [virtual]

return the number of parameters.

There is one parameter for this spectral model, namely the spectral index. So you supply a unit length vector when using these functions. Otherwise an exception (AipsError) may be thrown.

Implements casa::SpectralModel.

virtual Bool casa::SpectralIndex::ok ( ) const [virtual]

Function which checks the internal data of this class for consistant values.

Returns True if everything is fine otherwise returns False.

Reimplemented from casa::SpectralModel.

SpectralIndex& casa::SpectralIndex::operator= ( const SpectralIndex other)

The assignment operator uses copy semantics.

virtual Vector<Double> casa::SpectralIndex::parameters ( ) const [virtual]

Implements casa::SpectralModel.

virtual Double casa::SpectralIndex::sample ( const MFrequency centerFrequency) const [virtual]

Return the scaling factor that indicates what proportion of the flux is at the specified frequency.

ie. if the centreFrequency argument is the reference frequency then this function will always return one. At other frequencies it will return a non-negative number.

Implements casa::SpectralModel.

virtual void casa::SpectralIndex::sample ( Vector< Double > &  scale,
const Vector< MFrequency::MVType > &  frequencies,
const MFrequency::Ref refFrame 
) const [virtual]

Same as the previous function except that many frequencies can be sampled at once.

The reference frame must be the same for all the specified frequencies. Uses a customised implementation for improved speed.

Implements casa::SpectralModel.

virtual void casa::SpectralIndex::setErrors ( const Vector< Double > &  newSpectralErrs) [virtual]

Implements casa::SpectralModel.

void casa::SpectralIndex::setIndex ( const Double newIndex)
virtual void casa::SpectralIndex::setParameters ( const Vector< Double > &  newSpectralParms) [virtual]

Implements casa::SpectralModel.

virtual Bool casa::SpectralIndex::toRecord ( String error,
RecordInterface outRecord 
) const [virtual]

Convert the class to an Record representation.

The input record may already contain fields and these fields may be silently overridden. New fields may be added to the input Record. If the transformation succeeds then the error String is unchanged and the function returns True. Otherwise the function returns False and appends an error message to the supplied String giving the reason why the conversion failed.

Implements casa::SpectralModel.

return the actual spectral type ie., ComponentType::SPECTRAL_INDEX

Implements casa::SpectralModel.


Member Data Documentation

Definition at line 240 of file SpectralIndex.h.

Definition at line 239 of file SpectralIndex.h.


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