ROOT   Reference Guide
TVirtualFFT Class Referenceabstract

TVirtualFFT is an interface class for Fast Fourier Transforms.

The default FFT library is FFTW. To use it, FFTW3 library should already be installed, and ROOT should be have fftw3 module enabled, with the directories of fftw3 include file and library specified (see installation instructions). Function SetDefaultFFT() allows to change the default library.

## Available transform types:

FFT:

• "C2CFORWARD" - a complex input/output discrete Fourier transform (DFT) in one or more dimensions, -1 in the exponent
• "C2CBACKWARD"- a complex input/output discrete Fourier transform (DFT) in one or more dimensions, +1 in the exponent
• "R2C" - a real-input/complex-output discrete Fourier transform (DFT) in one or more dimensions,
• "C2R" - inverse transforms to "R2C", taking complex input (storing the non-redundant half of a logically Hermitian array) to real output
• "R2HC" - a real-input DFT with output in ¡Èhalfcomplex¡É format, i.e. real and imaginary parts for a transform of size n stored as r0, r1, r2, ..., rn/2, i(n+1)/2-1, ..., i2, i1
• "HC2R" - computes the reverse of FFTW_R2HC, above
• "DHT" - computes a discrete Hartley transform

## Sine/cosine transforms:

Different types of transforms are specified by parameter kind of the SineCosine() static function. 4 different kinds of sine and cosine transforms are available

• DCT-I (REDFT00 in FFTW3 notation)- kind=0
• DCT-II (REDFT01 in FFTW3 notation)- kind=1
• DCT-III(REDFT10 in FFTW3 notation)- kind=2
• DCT-IV (REDFT11 in FFTW3 notation)- kind=3
• DST-I (RODFT00 in FFTW3 notation)- kind=4
• DST-II (RODFT01 in FFTW3 notation)- kind=5
• DST-III(RODFT10 in FFTW3 notation)- kind=6
• DST-IV (RODFT11 in FFTW3 notation)- kind=7

Formulas and detailed descriptions can be found in the chapter "What FFTW really computes" of the FFTW manual

NOTE: FFTW computes unnormalized transforms, so doing a transform, followed by its inverse will give the original array, multiplied by normalization constant (transform size(N) for FFT, 2*(N-1) for DCT-I, 2*(N+1) for DST-I, 2*N for other sine/cosine transforms)

## How to use it:

Call to the static function FFT returns a pointer to a fast Fourier transform with requested parameters. Call to the static function SineCosine returns a pointer to a sine or cosine transform with requested parameters. Example:

{
Int_t N = 10; Double_t *in = new Double_t[N];
TVirtualFFT *fftr2c = TVirtualFFT::FFT(1, &N, "R2C");
fftr2c->SetPoints(in);
fftr2c->Transform();
Double_t re, im;
for (Int_t i=0; i<N; i++)
fftr2c->GetPointComplex(i, re, im);
...
fftr2c->SetPoints(in2);
...
fftr2c->SetPoints(in3);
...
}
#define N
TVirtualFFT is an interface class for Fast Fourier Transforms.
Definition: TVirtualFFT.h:88
static TVirtualFFT * FFT(Int_t ndim, Int_t *n, Option_t *option)
Returns a pointer to the FFT of requested size and type.
virtual void SetPoints(const Double_t *data)=0
virtual void Transform()=0
virtual void GetPointComplex(Int_t ipoint, Double_t &re, Double_t &im, Bool_t fromInput=kFALSE) const =0

Different options are explained in the function comments

Definition at line 88 of file TVirtualFFT.h.

## Public Member Functions

TVirtualFFT ()

virtual ~TVirtualFFT ()
destructor More...

virtual Int_tGetN () const =0

virtual Int_t GetNdim () const =0

virtual void GetPointComplex (const Int_t *ipoint, Double_t &re, Double_t &im, Bool_t fromInput=kFALSE) const =0

virtual void GetPointComplex (Int_t ipoint, Double_t &re, Double_t &im, Bool_t fromInput=kFALSE) const =0

virtual Double_t GetPointReal (const Int_t *ipoint, Bool_t fromInput=kFALSE) const =0

virtual Double_t GetPointReal (Int_t ipoint, Bool_t fromInput=kFALSE) const =0

virtual void GetPoints (Double_t *data, Bool_t fromInput=kFALSE) const =0

virtual void GetPointsComplex (Double_t *data, Bool_t fromInput=kFALSE) const =0

virtual void GetPointsComplex (Double_t *re, Double_t *im, Bool_t fromInput=kFALSE) const =0

virtual Double_tGetPointsReal (Bool_t fromInput=kFALSE) const =0

virtual Int_t GetSign () const =0

virtual Option_tGetTransformFlag () const =0

virtual Option_tGetType () const =0

virtual void Init (Option_t *flag, Int_t sign, const Int_t *kind)=0

TClassIsA () const override

virtual Bool_t IsInplace () const =0

virtual void SetPoint (const Int_t *ipoint, Double_t re, Double_t im=0)=0

virtual void SetPoint (Int_t ipoint, Double_t re, Double_t im=0)=0

virtual void SetPointComplex (Int_t ipoint, TComplex &c)=0

virtual void SetPoints (const Double_t *data)=0

virtual void SetPointsComplex (const Double_t *re, const Double_t *im)=0

void Streamer (TBuffer &) override
Stream an object of class TObject. More...

void StreamerNVirtual (TBuffer &ClassDef_StreamerNVirtual_b)

virtual void Transform ()=0

Public Member Functions inherited from TObject
TObject ()
TObject constructor. More...

TObject (const TObject &object)
TObject copy ctor. More...

virtual ~TObject ()
TObject destructor. More...

void AbstractMethod (const char *method) const
Use this method to implement an "abstract" method that you don't want to leave purely abstract. More...

Append graphics object to current pad. More...

virtual void Browse (TBrowser *b)
Browse object. May be overridden for another default action. More...

ULong_t CheckedHash ()
Check and record whether this class has a consistent Hash/RecursiveRemove setup (*) and then return the regular Hash value for this object. More...

virtual const char * ClassName () const
Returns name of class to which the object belongs. More...

virtual void Clear (Option_t *="")

virtual TObjectClone (const char *newname="") const
Make a clone of an object using the Streamer facility. More...

virtual Int_t Compare (const TObject *obj) const
Compare abstract method. More...

virtual void Copy (TObject &object) const
Copy this to obj. More...

virtual void Delete (Option_t *option="")
Delete this object. More...

virtual Int_t DistancetoPrimitive (Int_t px, Int_t py)
Computes distance from point (px,py) to the object. More...

virtual void Draw (Option_t *option="")
Default Draw method for all objects. More...

virtual void DrawClass () const
Draw class inheritance tree of the class to which this object belongs. More...

virtual TObjectDrawClone (Option_t *option="") const
Draw a clone of this object in the current selected pad with: gROOT->SetSelectedPad(c1). More...

virtual void Dump () const
Dump contents of object on stdout. More...

virtual void Error (const char *method, const char *msgfmt,...) const
Issue error message. More...

virtual void Execute (const char *method, const char *params, Int_t *error=nullptr)
Execute method on this object with the given parameter string, e.g. More...

virtual void Execute (TMethod *method, TObjArray *params, Int_t *error=nullptr)
Execute method on this object with parameters stored in the TObjArray. More...

virtual void ExecuteEvent (Int_t event, Int_t px, Int_t py)
Execute action corresponding to an event at (px,py). More...

virtual void Fatal (const char *method, const char *msgfmt,...) const
Issue fatal error message. More...

virtual TObjectFindObject (const char *name) const
Must be redefined in derived classes. More...

virtual TObjectFindObject (const TObject *obj) const
Must be redefined in derived classes. More...

virtual Option_tGetDrawOption () const
Get option used by the graphics system to draw this object. More...

virtual const char * GetIconName () const
Returns mime type name of object. More...

virtual const char * GetName () const
Returns name of object. More...

virtual char * GetObjectInfo (Int_t px, Int_t py) const
Returns string containing info about the object at position (px,py). More...

virtual Option_tGetOption () const

virtual const char * GetTitle () const
Returns title of object. More...

virtual UInt_t GetUniqueID () const
Return the unique object id. More...

virtual Bool_t HandleTimer (TTimer *timer)
Execute action in response of a timer timing out. More...

virtual ULong_t Hash () const
Return hash value for this object. More...

Bool_t HasInconsistentHash () const
Return true is the type of this object is known to have an inconsistent setup for Hash and RecursiveRemove (i.e. More...

virtual void Info (const char *method, const char *msgfmt,...) const
Issue info message. More...

virtual Bool_t InheritsFrom (const char *classname) const
Returns kTRUE if object inherits from class "classname". More...

virtual Bool_t InheritsFrom (const TClass *cl) const
Returns kTRUE if object inherits from TClass cl. More...

virtual void Inspect () const
Dump contents of this object in a graphics canvas. More...

void InvertBit (UInt_t f)

virtual TClassIsA () const

Bool_t IsDestructed () const
IsDestructed. More...

virtual Bool_t IsEqual (const TObject *obj) const
Default equal comparison (objects are equal if they have the same address in memory). More...

virtual Bool_t IsFolder () const
Returns kTRUE in case object contains browsable objects (like containers or lists of other objects). More...

R__ALWAYS_INLINE Bool_t IsOnHeap () const

virtual Bool_t IsSortable () const

R__ALWAYS_INLINE Bool_t IsZombie () const

virtual void ls (Option_t *option="") const
The ls function lists the contents of a class on stdout. More...

void MayNotUse (const char *method) const
Use this method to signal that a method (defined in a base class) may not be called in a derived class (in principle against good design since a child class should not provide less functionality than its parent, however, sometimes it is necessary). More...

virtual Bool_t Notify ()
This method must be overridden to handle object notification. More...

void Obsolete (const char *method, const char *asOfVers, const char *removedFromVers) const
Use this method to declare a method obsolete. More...

void operator delete (void *ptr)
Operator delete. More...

void operator delete[] (void *ptr)
Operator delete []. More...

void * operator new (size_t sz)

void * operator new (size_t sz, void *vp)

void * operator new[] (size_t sz)

void * operator new[] (size_t sz, void *vp)

TObjectoperator= (const TObject &rhs)
TObject assignment operator. More...

virtual void Paint (Option_t *option="")
This method must be overridden if a class wants to paint itself. More...

virtual void Pop ()
Pop on object drawn in a pad to the top of the display list. More...

virtual void Print (Option_t *option="") const
This method must be overridden when a class wants to print itself. More...

virtual Int_t Read (const char *name)
Read contents of object with specified name from the current directory. More...

virtual void RecursiveRemove (TObject *obj)
Recursively remove this object from a list. More...

void ResetBit (UInt_t f)

virtual void SaveAs (const char *filename="", Option_t *option="") const
Save this object in the file specified by filename. More...

virtual void SavePrimitive (std::ostream &out, Option_t *option="")
Save a primitive as a C++ statement(s) on output stream "out". More...

void SetBit (UInt_t f)

void SetBit (UInt_t f, Bool_t set)
Set or unset the user status bits as specified in f. More...

virtual void SetDrawOption (Option_t *option="")
Set drawing option for object. More...

virtual void SetUniqueID (UInt_t uid)
Set the unique object id. More...

virtual void Streamer (TBuffer &)
Stream an object of class TObject. More...

void StreamerNVirtual (TBuffer &ClassDef_StreamerNVirtual_b)

virtual void SysError (const char *method, const char *msgfmt,...) const
Issue system error message. More...

R__ALWAYS_INLINE Bool_t TestBit (UInt_t f) const

Int_t TestBits (UInt_t f) const

virtual void UseCurrentStyle ()
Set current style settings in this object This function is called when either TCanvas::UseCurrentStyle or TROOT::ForceStyle have been invoked. More...

virtual void Warning (const char *method, const char *msgfmt,...) const
Issue warning message. More...

virtual Int_t Write (const char *name=nullptr, Int_t option=0, Int_t bufsize=0)
Write this object to the current directory. More...

virtual Int_t Write (const char *name=nullptr, Int_t option=0, Int_t bufsize=0) const
Write this object to the current directory. More...

## Static Public Member Functions

static TClassClass ()

static const char * Class_Name ()

static constexpr Version_t Class_Version ()

static const char * DeclFileName ()

static TVirtualFFTFFT (Int_t ndim, Int_t *n, Option_t *option)
Returns a pointer to the FFT of requested size and type. More...

static TVirtualFFTGetCurrentTransform ()
static: return current fgFFT More...

static const char * GetDefaultFFT ()
static: return the name of the default fft More...

static void SetDefaultFFT (const char *name="")
static: set name of default fft More...

static void SetTransform (TVirtualFFT *fft)
static: set the current transfrom to parameter More...

static TVirtualFFTSineCosine (Int_t ndim, Int_t *n, Int_t *r2rkind, Option_t *option)
Returns a pointer to a sine or cosine transform of requested size and kind. More...

Static Public Member Functions inherited from TObject
static TClassClass ()

static const char * Class_Name ()

static constexpr Version_t Class_Version ()

static const char * DeclFileName ()

static Longptr_t GetDtorOnly ()
Return destructor only flag. More...

static Bool_t GetObjectStat ()
Get status of object stat flag. More...

static void SetDtorOnly (void *obj)
Set destructor only flag. More...

static void SetObjectStat (Bool_t stat)
Turn on/off tracking of objects in the TObjectTable. More...

## Static Protected Attributes

static TString fgDefault = ""

static TVirtualFFTfgFFT = nullptr

Public Types inherited from TObject
enum  {
kIsOnHeap = 0x01000000 , kNotDeleted = 0x02000000 , kZombie = 0x04000000 , kInconsistent = 0x08000000 ,
}

enum  { kSingleKey = (1ULL << ( 0 )) , kOverwrite = (1ULL << ( 1 )) , kWriteDelete = (1ULL << ( 2 )) }

enum  EDeprecatedStatusBits { kObjInCanvas = (1ULL << ( 3 )) }

enum  EStatusBits {
kCanDelete = (1ULL << ( 0 )) , kMustCleanup = (1ULL << ( 3 )) , kIsReferenced = (1ULL << ( 4 )) , kHasUUID = (1ULL << ( 5 )) ,
kCannotPick = (1ULL << ( 6 )) , kNoContextMenu = (1ULL << ( 8 )) , kInvalidObject = (1ULL << ( 13 ))
}

Protected Types inherited from TObject
enum  { kOnlyPrepStep = (1ULL << ( 3 )) }

Protected Member Functions inherited from TObject
virtual void DoError (int level, const char *location, const char *fmt, va_list va) const
Interface to ErrorHandler (protected). More...

void MakeZombie ()

#include <TVirtualFFT.h>

Inheritance diagram for TVirtualFFT:
[legend]

## ◆ TVirtualFFT()

 TVirtualFFT::TVirtualFFT ( )
inline

Definition at line 96 of file TVirtualFFT.h.

## ◆ ~TVirtualFFT()

 TVirtualFFT::~TVirtualFFT ( )
virtual

destructor

Definition at line 96 of file TVirtualFFT.cxx.

## ◆ Class()

 static TClass * TVirtualFFT::Class ( )
static
Returns
TClass describing this class

## ◆ Class_Name()

 static const char * TVirtualFFT::Class_Name ( )
static
Returns
Name of this class

## ◆ Class_Version()

 static constexpr Version_t TVirtualFFT::Class_Version ( )
inlinestaticconstexpr
Returns
Version of this class

Definition at line 132 of file TVirtualFFT.h.

## ◆ DeclFileName()

 static const char * TVirtualFFT::DeclFileName ( )
inlinestatic
Returns
Name of the file containing the class declaration

Definition at line 132 of file TVirtualFFT.h.

## ◆ FFT()

 TVirtualFFT * TVirtualFFT::FFT ( Int_t ndim, Int_t * n, Option_t * option )
static

Returns a pointer to the FFT of requested size and type.

Parameters
 [in] ndim number of transform dimensions [in] n sizes of each dimension (an array at least ndim long) [in] option consists of 3 parts - flag option and an option to create a new TVirtualFFT transform type option: Available transform types are: C2CForward, C2CBackward, C2R, R2C, R2HC, HC2R, DHT see class description for details flag option: choosing how much time should be spent in planning the transform: Possible options: "ES" (from "estimate") - no time in preparing the transform, but probably sub-optimal performance "M" (from "measure") - some time spend in finding the optimal way to do the transform "P" (from "patient") - more time spend in finding the optimal way to do the transform "EX" (from "exhaustive") - the most optimal way is found This option should be chosen depending on how many transforms of the same size and type are going to be done. Planning is only done once, for the first transform of this size and type. option allowing to choose between the global fgFFT and a new TVirtualFFT object "" - default, changes and returns the global fgFFT variable "K" (from "keep")- without touching the global fgFFT, creates and returns a new TVirtualFFT*. User is then responsible for deleting it.

Examples of valid options: "R2C ES K", "C2CF M", "DHT P K", etc.

Definition at line 131 of file TVirtualFFT.cxx.

## ◆ GetCurrentTransform()

 TVirtualFFT * TVirtualFFT::GetCurrentTransform ( )
static

static: return current fgFFT

Definition at line 348 of file TVirtualFFT.cxx.

## ◆ GetDefaultFFT()

 const char * TVirtualFFT::GetDefaultFFT ( )
static

static: return the name of the default fft

Definition at line 369 of file TVirtualFFT.cxx.

## ◆ GetN()

 virtual Int_t * TVirtualFFT::GetN ( ) const
pure virtual

## ◆ GetNdim()

 virtual Int_t TVirtualFFT::GetNdim ( ) const
pure virtual

## ◆ GetPointComplex() [1/2]

 virtual void TVirtualFFT::GetPointComplex ( const Int_t * ipoint, Double_t & re, Double_t & im, Bool_t fromInput = kFALSE ) const
pure virtual

## ◆ GetPointComplex() [2/2]

 virtual void TVirtualFFT::GetPointComplex ( Int_t ipoint, Double_t & re, Double_t & im, Bool_t fromInput = kFALSE ) const
pure virtual

## ◆ GetPointReal() [1/2]

 virtual Double_t TVirtualFFT::GetPointReal ( const Int_t * ipoint, Bool_t fromInput = kFALSE ) const
pure virtual

## ◆ GetPointReal() [2/2]

 virtual Double_t TVirtualFFT::GetPointReal ( Int_t ipoint, Bool_t fromInput = kFALSE ) const
pure virtual

## ◆ GetPoints()

 virtual void TVirtualFFT::GetPoints ( Double_t * data, Bool_t fromInput = kFALSE ) const
pure virtual

## ◆ GetPointsComplex() [1/2]

 virtual void TVirtualFFT::GetPointsComplex ( Double_t * data, Bool_t fromInput = kFALSE ) const
pure virtual

## ◆ GetPointsComplex() [2/2]

 virtual void TVirtualFFT::GetPointsComplex ( Double_t * re, Double_t * im, Bool_t fromInput = kFALSE ) const
pure virtual

## ◆ GetPointsReal()

 virtual Double_t * TVirtualFFT::GetPointsReal ( Bool_t fromInput = kFALSE ) const
pure virtual

## ◆ GetSign()

 virtual Int_t TVirtualFFT::GetSign ( ) const
pure virtual

## ◆ GetTransformFlag()

 virtual Option_t * TVirtualFFT::GetTransformFlag ( ) const
pure virtual

## ◆ GetType()

 virtual Option_t * TVirtualFFT::GetType ( ) const
pure virtual

## ◆ Init()

 virtual void TVirtualFFT::Init ( Option_t * flag, Int_t sign, const Int_t * kind )
pure virtual

## ◆ IsA()

 TClass * TVirtualFFT::IsA ( ) const
inlineoverridevirtual
Returns
TClass describing current object

Reimplemented from TObject.

Reimplemented in TFFTComplex, TFFTComplexReal, TFFTReal, and TFFTRealComplex.

Definition at line 132 of file TVirtualFFT.h.

## ◆ IsInplace()

 virtual Bool_t TVirtualFFT::IsInplace ( ) const
pure virtual

## ◆ SetDefaultFFT()

 void TVirtualFFT::SetDefaultFFT ( const char * name = "" )
static

static: set name of default fft

Definition at line 377 of file TVirtualFFT.cxx.

## ◆ SetPoint() [1/2]

 virtual void TVirtualFFT::SetPoint ( const Int_t * ipoint, Double_t re, Double_t im = 0 )
pure virtual

## ◆ SetPoint() [2/2]

 virtual void TVirtualFFT::SetPoint ( Int_t ipoint, Double_t re, Double_t im = 0 )
pure virtual

## ◆ SetPointComplex()

 virtual void TVirtualFFT::SetPointComplex ( Int_t ipoint, TComplex & c )
pure virtual

## ◆ SetPoints()

 virtual void TVirtualFFT::SetPoints ( const Double_t * data )
pure virtual

## ◆ SetPointsComplex()

 virtual void TVirtualFFT::SetPointsComplex ( const Double_t * re, const Double_t * im )
pure virtual

## ◆ SetTransform()

 void TVirtualFFT::SetTransform ( TVirtualFFT * fft )
static

static: set the current transfrom to parameter

Definition at line 361 of file TVirtualFFT.cxx.

## ◆ SineCosine()

 TVirtualFFT * TVirtualFFT::SineCosine ( Int_t ndim, Int_t * n, Int_t * r2rkind, Option_t * option )
static

Returns a pointer to a sine or cosine transform of requested size and kind.

Parameters:

Parameters
 [in] ndim number of transform dimensions [in] n sizes of each dimension (an array at least ndim long) [in] r2rkind transform kind for each dimension 4 different kinds of sine and cosine transforms are available DCT-I - kind=0 DCT-II - kind=1 DCT-III - kind=2 DCT-IV - kind=3 DST-I - kind=4 DST-II - kind=5 DST-III - kind=6 DST-IV - kind=7 [in] option : consists of 2 parts flag option and an option to create a new TVirtualFFT flag option: choosing how much time should be spent in planning the transform: Possible options: "ES" (from "estimate") - no time in preparing the transform, but probably sub-optimal performance "M" (from "measure") - some time spend in finding the optimal way to do the transform "P" (from "patient") - more time spend in finding the optimal way to do the transform "EX" (from "exhaustive") - the most optimal way is found This option should be chosen depending on how many transforms of the same size and type are going to be done. Planning is only done once, for the first transform of this size and type. option allowing to choose between the global fgFFT and a new TVirtualFFT object "" - default, changes and returns the global fgFFT variable "K" (from "keep")- without touching the global fgFFT, creates and returns a new TVirtualFFT*. User is then responsible for deleting it. Examples of valid options: "ES K", "EX", etc

Definition at line 279 of file TVirtualFFT.cxx.

## ◆ Streamer()

 void TVirtualFFT::Streamer ( TBuffer & R__b )
overridevirtual

Stream an object of class TObject.

Reimplemented from TObject.

Reimplemented in TFFTComplex, TFFTComplexReal, TFFTReal, and TFFTRealComplex.

## ◆ StreamerNVirtual()

 void TVirtualFFT::StreamerNVirtual ( TBuffer & ClassDef_StreamerNVirtual_b )
inline

Definition at line 132 of file TVirtualFFT.h.

## ◆ Transform()

 virtual void TVirtualFFT::Transform ( )
pure virtual

## ◆ fgDefault

 TString TVirtualFFT::fgDefault = ""
staticprotected

Definition at line 92 of file TVirtualFFT.h.

## ◆ fgFFT

 TVirtualFFT * TVirtualFFT::fgFFT = nullptr
staticprotected

Definition at line 91 of file TVirtualFFT.h.

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