casa::Lattice< T > Class Template Reference
[Lattices]

#include <Lattice.h>

Inheritance diagram for casa::Lattice< T >:

[legend]Collaboration diagram for casa::Lattice< T >:

[legend]List of all members.

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Detailed Description

template<class T>
class casa::Lattice< T >

A templated, abstract base class for array-like objects.

Intended use:

Part of API

Review Status

Reviewed By:

Peter Barnes

Date Reviewed:

1999/10/30

Test programs:

tArrayLattice

Demo programs:

dLattice

Prerequisite

• IPosition
• Array
• LatticeBase
• Abstract Base class Inheritance - try "Advanced C++" by James O. Coplien, Ch. 5.

Etymology

Lattice: "A regular, periodic configuration of points, particles, or objects, throughout an area of a space.\.." (American Heritage Directory) This definition matches our own: an n-dimensional arrangement of items, on regular orthogonal axes.

Synopsis

This pure abstract base class defines the operations which may be performed on any concrete class derived from it. It has only a few non-pure virtual member functions. The fundamental contribution of this class, therefore, is that it defines the operations derived classes must provide:

• how to extract a "slice" (or sub-array, or subsection) from a Lattice.
• how to copy a slice in.
• how to get and put a single element
• how to apply a function to all elements
• various shape related functions.

The base class LatticeBase contains several functions not dependent on the template parameter. Tip: Lattices always have a zero origin.

Example

Because Lattice is an abstract base class, an actual instance of this class cannot be constructed. However the interface it defines can be used inside a function. This is always recommended as it allows functions which have Lattices as arguments to work for any derived class.

I will give a few examples here and then refer the reader to the ArrayLattice class (a memory resident Lattice) and the PagedArray class (a disk based Lattice) which contain further examples with concrete classes (rather than an abstract one). All the examples shown below are used in the dLattice.cc demo program.

Example 1:

This example calculates the mean of the Lattice. Because Lattices can be too large to fit into physical memory it is not good enough to simply use getSlice to read all the elements into an Array. Instead the Lattice is accessed in chunks which can fit into memory (the size is determined by the advisedMaxPixels and niceCursorShape functions). The LatticeIterator::cursor() function then returns each of these chunks as an Array and the standard Array based functions are used to calculate the mean on each of these chunks. Functions like this one are the recommended way to access Lattices as the LatticeIterator will correctly setup any required caches.

    Complex latMean(const Lattice<Complex>& lat) {
      const uInt cursorSize = lat.advisedMaxPixels();
      const IPosition cursorShape = lat.niceCursorShape(cursorSize);
      const IPosition latticeShape = lat.shape();
      Complex currentSum = 0.0f;
      uInt nPixels = 0u;
      RO_LatticeIterator<Complex> iter(lat, 
                                   LatticeStepper(latticeShape, cursorShape));
      for (iter.reset(); !iter.atEnd(); iter++){
        currentSum += sum(iter.cursor());
        nPixels += iter.cursor().nelements();
      }
      return currentSum/nPixels;
    }

Example 2:

Sometimes it will be neccesary to access slices of a Lattice in a nearly random way. Often this can be done using the subSection commands in the LatticeStepper class. But it is also possible to use the getSlice and putSlice functions. The following example does a two-dimensional Real to Complex Fourier transform. This example is restricted to four-dimensional Arrays (unlike the previous example) and does not set up any caches (caching is currently only used with PagedArrays). So only use getSlice and putSlice when things cannot be done using LatticeIterators.

    void FFT2DReal2Complex(Lattice<Complex>& result, 
                       const Lattice<Float>& input){
      AlwaysAssert(input.ndim() == 4, AipsError);
      const IPosition shape = input.shape();
      const uInt nx = shape(0);
      AlwaysAssert (nx > 1, AipsError);
      const uInt ny = shape(1);
      AlwaysAssert (ny > 1, AipsError);
      const uInt npol = shape(2);
      const uInt nchan = shape(3); 
      const IPosition resultShape = result.shape();
      AlwaysAssert(resultShape.nelements() == 4, AipsError);
      AlwaysAssert(resultShape(3) == nchan, AipsError);
      AlwaysAssert(resultShape(2) == npol, AipsError);
      AlwaysAssert(resultShape(1) == ny, AipsError);
      AlwaysAssert(resultShape(0) == nx/2 + 1, AipsError);
   
      const IPosition inputSliceShape(4,nx,ny,1,1);
      const IPosition resultSliceShape(4,nx/2+1,ny,1,1);
      COWPtr<Array<Float> > 
        inputArrPtr(new Array<Float>(inputSliceShape.nonDegenerate()));
      Array<Complex> resultArray(resultSliceShape.nonDegenerate());
      FFTServer<Float, Complex> FFT2D(inputSliceShape.nonDegenerate());
     
      IPosition start(4,0);
      Bool isARef;
      for (uInt c = 0; c < nchan; c++){
        for (uInt p = 0; p < npol; p++){
          isARef = input.getSlice(inputArrPtr,
                                  Slicer(start,inputSliceShape), True);
          FFT2D.fft(resultArray, *inputArrPtr);
          result.putSlice(resultArray, start);
          start(2) += 1;
        }
        start(2) = 0;
        start(3) += 1;
      }
    }

Note that the LatticeFFT class offers a nice way to do lattice based FFTs.

Example 3:

Occasionally you may want to access a few elements of a Lattice without all the difficulty involved in setting up Iterators or calling getSlice and putSlice. This is demonstrated in the example below. Setting a single element can be done with the putAt function, while getting a single element can be done with the parenthesis operator. Using these functions to access many elements of a Lattice is not recommended as this is the slowest access method.

In this example an ideal point spread function will be inserted into an empty Lattice. As with the previous examples all the action occurs inside a function because Lattice is an interface (abstract) class.

    void makePsf(Lattice<Float>& psf) {
      const IPosition centrePos = psf.shape()/2;
      psf.set(0.0f);       // this sets all the elements to zero
                           // As it uses a LatticeIterator it is efficient
      psf.putAt (1, centrePos);  // This sets just the centre element to one
      AlwaysAssert(near(psf(centrePos), 1.0f, 1E-6), AipsError);
      AlwaysAssert(near(psf(centrePos*0), 0.0f, 1E-6), AipsError);
    }

Motivation

Creating an abstract base class which provides a common interface between memory and disk based arrays has a number of advantages.

• It allows functions common to all arrays to be written independent of the way the data is stored. This is illustrated in the three examples above.
• It reduces the learning curve for new users who only have to become familiar with one interface (ie. Lattice) rather than distinct interfaces for different array types.

To Do

• Make PagedArray cache functions virtual in this base class.

Definition at line 230 of file Lattice.h.

	Lattice (const Lattice< T > &)
	Copy constructor and assignment can only be used by derived classes.
Lattice< T > &	operator= (const Lattice< T > &)
Public Member Functions
virtual	~Lattice ()
	a virtual destructor is needed so that it will use the actual destructor in the derived class
virtual Lattice< T > *	clone () const=0
	Make a copy of the derived object (reference semantics).
virtual void	putAt (const T &value, const IPosition &where)
	Put the value of a single element.
virtual void	set (const T &value)
	Set all elements in the Lattice to the given value.
virtual void	copyData (const Lattice< T > &from)
	Copy the data from the given lattice to this one.
virtual void	copyDataTo (Lattice< T > &to) const
	Copy the data from this lattice to the given lattice.
virtual uInt	advisedMaxPixels () const
	This function returns the advised maximum number of pixels to include in the cursor of an iterator.
virtual LatticeIterInterface< T > *	makeIter (const LatticeNavigator &navigator, Bool useRef) const
	These functions are used by the LatticeIterator class to generate an iterator of the correct type for a specified Lattice.
template<>
void	handleMathTo (Lattice< Bool > &to, int oper) const
T	operator() (const IPosition &where) const
	Return the value of the single element located at the argument IPosition.
virtual T	getAt (const IPosition &where) const
Bool	get (COWPtr< Array< T > > &buffer, Bool removeDegenerateAxes=False) const
	Functions which extract an Array of values from a Lattice.
Bool	getSlice (COWPtr< Array< T > > &buffer, const Slicer &section, Bool removeDegenerateAxes=False) const
Bool	getSlice (COWPtr< Array< T > > &buffer, const IPosition &start, const IPosition &shape, Bool removeDegenerateAxes=False) const
Bool	getSlice (COWPtr< Array< T > > &buffer, const IPosition &start, const IPosition &shape, const IPosition &stride, Bool removeDegenerateAxes=False) const
Bool	get (Array< T > &buffer, Bool removeDegenerateAxes=False)
Bool	getSlice (Array< T > &buffer, const Slicer &section, Bool removeDegenerateAxes=False)
Bool	getSlice (Array< T > &buffer, const IPosition &start, const IPosition &shape, Bool removeDegenerateAxes=False)
Bool	getSlice (Array< T > &buffer, const IPosition &start, const IPosition &shape, const IPosition &stride, Bool removeDegenerateAxes=False)
Array< T >	get (Bool removeDegenerateAxes=False) const
Array< T >	getSlice (const Slicer &section, Bool removeDegenerateAxes=False) const
Array< T >	getSlice (const IPosition &start, const IPosition &shape, Bool removeDegenerateAxes=False) const
Array< T >	getSlice (const IPosition &start, const IPosition &shape, const IPosition &stride, Bool removeDegenerateAxes=False) const
void	putSlice (const Array< T > &sourceBuffer, const IPosition &where, const IPosition &stride)
	A function which places an Array of values within this instance of the Lattice at the location specified by the IPosition "where", incrementing by "stride".
void	putSlice (const Array< T > &sourceBuffer, const IPosition &where)
void	put (const Array< T > &sourceBuffer)
virtual void	apply (T(*function)(T))
	Replace every element, x, of the Lattice with the result of f(x).
virtual void	apply (T(*function)(const T &))
virtual void	apply (const Functional< T, T > &function)
void	operator+= (const Lattice< T > &other)
	Add, subtract, multiple, or divide by another Lattice.
void	operator-= (const Lattice< T > &other)
void	operator *= (const Lattice< T > &other)
void	operator/= (const Lattice< T > &other)
virtual Bool	doGetSlice (Array< T > &buffer, const Slicer &section)=0
	The functions (in the derived classes) doing the actual work.
virtual void	doPutSlice (const Array< T > &buffer, const IPosition &where, const IPosition &stride)=0
Protected Member Functions
	Lattice ()
	Define default constructor to satisfy compiler.
virtual void	handleMath (const Lattice< T > &from, int oper)
	Handle the Math operators (+=, -=, *=, /=).
virtual void	handleMathTo (Lattice< T > &to, int oper) const

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Constructor & Destructor Documentation

template<class T>

virtual casa::Lattice< T >::~Lattice

(

)

[virtual]

a virtual destructor is needed so that it will use the actual destructor in the derived class

template<class T>

casa::Lattice< T >::Lattice

(

)

[inline, protected]

Define default constructor to satisfy compiler.

Definition at line 403 of file Lattice.h.

template<class T>

casa::Lattice< T >::Lattice

(

const Lattice< T > &

)

[inline, protected]

Copy constructor and assignment can only be used by derived classes.

Definition at line 415 of file Lattice.h.

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Member Function Documentation

template<class T>

virtual Lattice<T>* casa::Lattice< T >::clone

(

)

const [pure virtual]

Make a copy of the derived object (reference semantics).

Implements casa::LatticeBase.

Referenced by casa::LatticeModel::setModel(), casa::CEMemModel::setModel(), and casa::IncCEMemModel::setModel().

template<class T>

T casa::Lattice< T >::operator()

(

const IPosition &

where

)

const

Return the value of the single element located at the argument IPosition.

The default implementation uses getSlice.

template<class T>

virtual T casa::Lattice< T >::getAt

(

const IPosition &

where

)

const [virtual]

template<class T>

virtual void casa::Lattice< T >::putAt	(	const T &	value,
		const IPosition &	where
	)			[virtual]

Put the value of a single element.

The default implementation uses putSlice.

template<class T>

Bool casa::Lattice< T >::get	(	COWPtr< Array< T > > &	buffer,
		Bool	removeDegenerateAxes = False
	)			const

Functions which extract an Array of values from a Lattice.

All the IPosition arguments must have the same number of axes as the underlying Lattice, otherwise, an exception is thrown.
The parameters are:

• buffer: a COWPtr<Array<T>> or an Array<T>. See example 2 above for an example.
• start: The starting position (or Bottom Left Corner), within the Lattice, of the data to be extracted.
• shape: The shape of the data to be extracted. This is not a position within the Lattice but the actual shape the buffer will have after this function is called. This argument added to the "start" argument should be the "Top Right Corner".
• stride: The increment for each axis. A stride of one will return every data element, a stride of two will return every other element. The IPosition elements may be different for each respective axis. Thus, a stride of IPosition(3,1,2,3) says: fill the buffer with every element whose position has a first index between start(0) and start(0)+shape(0), a second index which is every other element between start(1) and (start(1)+shape(1))*2, and a third index of every third element between start(2) and (start(2)+shape(2))*3.
• section: Another way of specifying the start, shape and stride
• removeDegenerateAxes: a Bool which dictates whether to remove "empty" axis created in buffer. (e.g. extracting an n-dimensional from an (n+1)-dimensional will fill 'buffer' with an array that has a degenerate axis (i.e. one axis will have a length = 1.) Setting removeDegenerateAxes = True will return a buffer with a shape that doesn't reflect these superfluous axes.)

The derived implementations of these functions return 'True' if "buffer" is a reference to Lattice data and 'False' if it is a copy.

template<class T>

Bool casa::Lattice< T >::getSlice	(	COWPtr< Array< T > > &	buffer,
		const Slicer &	section,
		Bool	removeDegenerateAxes = False
	)			const

template<class T>

Bool casa::Lattice< T >::getSlice	(	COWPtr< Array< T > > &	buffer,
		const IPosition &	start,
		const IPosition &	shape,
		Bool	removeDegenerateAxes = False
	)			const

template<class T>

Bool casa::Lattice< T >::getSlice	(	COWPtr< Array< T > > &	buffer,
		const IPosition &	start,
		const IPosition &	shape,
		const IPosition &	stride,
		Bool	removeDegenerateAxes = False
	)			const

template<class T>

Bool casa::Lattice< T >::get	(	Array< T > &	buffer,
		Bool	removeDegenerateAxes = False
	)

template<class T>

Bool casa::Lattice< T >::getSlice	(	Array< T > &	buffer,
		const Slicer &	section,
		Bool	removeDegenerateAxes = False
	)

template<class T>

Bool casa::Lattice< T >::getSlice	(	Array< T > &	buffer,
		const IPosition &	start,
		const IPosition &	shape,
		Bool	removeDegenerateAxes = False
	)

template<class T>

Bool casa::Lattice< T >::getSlice	(	Array< T > &	buffer,
		const IPosition &	start,
		const IPosition &	shape,
		const IPosition &	stride,
		Bool	removeDegenerateAxes = False
	)

template<class T>

Array<T> casa::Lattice< T >::get

(

Bool

removeDegenerateAxes = False

)

const

template<class T>

Array<T> casa::Lattice< T >::getSlice	(	const Slicer &	section,
		Bool	removeDegenerateAxes = False
	)			const

template<class T>

Array<T> casa::Lattice< T >::getSlice	(	const IPosition &	start,
		const IPosition &	shape,
		Bool	removeDegenerateAxes = False
	)			const

template<class T>

Array<T> casa::Lattice< T >::getSlice	(	const IPosition &	start,
		const IPosition &	shape,
		const IPosition &	stride,
		Bool	removeDegenerateAxes = False
	)			const

template<class T>

void casa::Lattice< T >::putSlice	(	const Array< T > &	sourceBuffer,
		const IPosition &	where,
		const IPosition &	stride
	)			[inline]

A function which places an Array of values within this instance of the Lattice at the location specified by the IPosition "where", incrementing by "stride".

All of the IPosition arguments must be of the same dimensionality as the Lattice. The sourceBuffer array may (and probably will) have less axes than the Lattice. The stride defaults to one if not specified.

Definition at line 325 of file Lattice.h.

template<class T>

void casa::Lattice< T >::putSlice	(	const Array< T > &	sourceBuffer,
		const IPosition &	where
	)

template<class T>

void casa::Lattice< T >::put

(

const Array< T > &

sourceBuffer

)

template<class T>

virtual void casa::Lattice< T >::set

(

const T &

value

)

[virtual]

Set all elements in the Lattice to the given value.

template<class T>

virtual void casa::Lattice< T >::apply

(

T(*)(T)

function

)

[virtual]

Replace every element, x, of the Lattice with the result of f(x).

You must pass in the address of the function -- so the function must be declared and defined in the scope of your program. All versions of apply require a function that accepts a single argument of type T (the Lattice template type) and return a result of the same type. The first apply expects a function with an argument passed by value; the second expects the argument to be passed by const reference; the third requires an instance of the class Functional<T,T>. The first form ought to run faster for the built-in types, which may be an issue for large Lattices stored in memory, where disk access is not an issue.

template<class T>

virtual void casa::Lattice< T >::apply

(

T(*)(const T &)

function

)

[virtual]

template<class T>

virtual void casa::Lattice< T >::apply

(

const Functional< T, T > &

function

)

[virtual]

template<class T>

void casa::Lattice< T >::operator+=

(

const Lattice< T > &

other

)

[inline]

Add, subtract, multiple, or divide by another Lattice.

The other Lattice can be a scalar (e.g. the result of LatticeExpr). Possible masks are not taken into account.

Definition at line 357 of file Lattice.h.

template<class T>

void casa::Lattice< T >::operator-=

(

const Lattice< T > &

other

)

[inline]

Definition at line 359 of file Lattice.h.

template<class T>

void casa::Lattice< T >::operator *=

(

const Lattice< T > &

other

)

[inline]

Definition at line 361 of file Lattice.h.

template<class T>

void casa::Lattice< T >::operator/=

(

const Lattice< T > &

other

)

[inline]

Definition at line 363 of file Lattice.h.

template<class T>

virtual void casa::Lattice< T >::copyData

(

const Lattice< T > &

from

)

[virtual]

Copy the data from the given lattice to this one.

The default implementation uses function copyDataTo.

template<class T>

virtual void casa::Lattice< T >::copyDataTo

(

Lattice< T > &

to

)

const [virtual]

Copy the data from this lattice to the given lattice.

The default implementation only copies data (thus no mask, etc.).

template<class T>

virtual uInt casa::Lattice< T >::advisedMaxPixels

(

)

const [virtual]

This function returns the advised maximum number of pixels to include in the cursor of an iterator.

The default implementation returns a number that is a power of two and includes enough pixels to consume between 4 and 8 MBytes of memory.

Implements casa::LatticeBase.

template<class T>

virtual LatticeIterInterface<T>* casa::Lattice< T >::makeIter	(	const LatticeNavigator &	navigator,
		Bool	useRef
	)			const [virtual]

These functions are used by the LatticeIterator class to generate an iterator of the correct type for a specified Lattice.

Not recommended for general use.
The default implementation creates a LatticeIterInterface object.

template<class T>

virtual Bool casa::Lattice< T >::doGetSlice	(	Array< T > &	buffer,
		const Slicer &	section
	)			[pure virtual]

The functions (in the derived classes) doing the actual work.

These functions are public, so they can be used internally in the various Lattice classes, which is especially useful for doGetSlice.
However, doGetSlice does not call Slicer::inferShapeFromSource to fill in possible unspecified section values. Therefore one should normally use one of the get(Slice) functions. doGetSlice should be used with care and only when performance is an issue.

template<class T>

virtual void casa::Lattice< T >::doPutSlice	(	const Array< T > &	buffer,
		const IPosition &	where,
		const IPosition &	stride
	)			[pure virtual]

Referenced by casa::Lattice< std::complex< Float > >::putSlice().

template<class T>

virtual void casa::Lattice< T >::handleMath	(	const Lattice< T > &	from,
		int	oper
	)			[protected, virtual]

Handle the Math operators (+=, -=, *=, /=).

They work similarly to copyData(To). However, they are not defined for Bool types, thus specialized below.

Referenced by casa::Lattice< std::complex< Float > >::operator *=(), casa::Lattice< std::complex< Float > >::operator+=(), casa::Lattice< std::complex< Float > >::operator-=(), and casa::Lattice< std::complex< Float > >::operator/=().

template<class T>

virtual void casa::Lattice< T >::handleMathTo	(	Lattice< T > &	to,
		int	oper
	)			const [protected, virtual]

template<class T>

Lattice<T>& casa::Lattice< T >::operator=

(

const Lattice< T > &

)

[inline, protected]

Definition at line 416 of file Lattice.h.

template<>

void casa::Lattice< Bool >::handleMathTo	(	Lattice< Bool > &	to,
		int	oper
	)			const [inline]

Definition at line 423 of file Lattice.h.

References casa::LatticeBase::throwBoolMath().

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

• lattices/implement/Lattices/Lattice.h

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