GeographicLib  1.37
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GeographicLib::Accumulator< T > Class Template Reference

An accumulator for sums. More...

#include <GeographicLib/Accumulator.hpp>

Public Member Functions

 Accumulator (T y=T(0))
 
Accumulatoroperator= (T y)
 
operator() () const
 
operator() (T y) const
 
Accumulatoroperator+= (T y)
 
Accumulatoroperator-= (T y)
 
Accumulatoroperator*= (int n)
 
bool operator== (T y) const
 
bool operator!= (T y) const
 
bool operator< (T y) const
 
bool operator<= (T y) const
 
bool operator> (T y) const
 
bool operator>= (T y) const
 

Detailed Description

template<typename T = Math::real>
class GeographicLib::Accumulator< T >

An accumulator for sums.

This allow many numbers of floating point type T to be added together with twice the normal precision. Thus if T is double, the effective precision of the sum is 106 bits or about 32 decimal places.

The implementation follows J. R. Shewchuk, Adaptive Precision Floating-Point Arithmetic and Fast Robust Geometric Predicates, Discrete & Computational Geometry 18(3) 305–363 (1997).

Approximate timings (summing a vector<double>)

In the documentation of the member functions, sum stands for the value currently held in the accumulator.

Example of use:

// Example of using the GeographicLib::Accumulator class
#include <iostream>
#include <exception>
using namespace std;
using namespace GeographicLib;
int main() {
try {
// Compare using Accumulator and ordinary summation for a sum of large and
// small terms.
double sum = 0;
Accumulator<> acc = 0;
sum += 1e20; sum += 1; sum += 2; sum += 100; sum += 5000; sum += -1e20;
acc += 1e20; acc += 1; acc += 2; acc += 100; acc += 5000; acc += -1e20;
cout << sum << " " << acc() << "\n";
}
catch (const exception& e) {
cerr << "Caught exception: " << e.what() << "\n";
return 1;
}
return 0;
}

Definition at line 40 of file Accumulator.hpp.

Constructor & Destructor Documentation

template<typename T = Math::real>
GeographicLib::Accumulator< T >::Accumulator ( y = T(0))
inline

Construct from a T. This is not declared explicit, so that you can write Accumulator<double> a = 5;.

Parameters
[in]yset sum = y.

Definition at line 101 of file Accumulator.hpp.

Member Function Documentation

template<typename T = Math::real>
Accumulator& GeographicLib::Accumulator< T >::operator= ( y)
inline

Set the accumulator to a number.

Parameters
[in]yset sum = y.

Definition at line 110 of file Accumulator.hpp.

template<typename T = Math::real>
T GeographicLib::Accumulator< T >::operator() ( ) const
inline

Return the value held in the accumulator.

Returns
sum.

Definition at line 116 of file Accumulator.hpp.

template<typename T = Math::real>
T GeographicLib::Accumulator< T >::operator() ( y) const
inline

Return the result of adding a number to sum (but don't change sum).

Parameters
[in]ythe number to be added to the sum.
Returns
sum + y.

Definition at line 123 of file Accumulator.hpp.

template<typename T = Math::real>
Accumulator& GeographicLib::Accumulator< T >::operator+= ( y)
inline

Add a number to the accumulator.

Parameters
[in]yset sum += y.

Definition at line 129 of file Accumulator.hpp.

template<typename T = Math::real>
Accumulator& GeographicLib::Accumulator< T >::operator-= ( y)
inline

Subtract a number from the accumulator.

Parameters
[in]yset sum -= y.

Definition at line 135 of file Accumulator.hpp.

template<typename T = Math::real>
Accumulator& GeographicLib::Accumulator< T >::operator*= ( int  n)
inline

Multiply accumulator by an integer. To avoid loss of accuracy, use only integers such that n × T is exactly representable as a T (i.e., ± powers of two). Use n = −1 to negate sum.

Parameters
[in]nset sum *= n.

Definition at line 143 of file Accumulator.hpp.

template<typename T = Math::real>
bool GeographicLib::Accumulator< T >::operator== ( y) const
inline

Test equality of an Accumulator with a number.

Definition at line 147 of file Accumulator.hpp.

template<typename T = Math::real>
bool GeographicLib::Accumulator< T >::operator!= ( y) const
inline

Test inequality of an Accumulator with a number.

Definition at line 151 of file Accumulator.hpp.

template<typename T = Math::real>
bool GeographicLib::Accumulator< T >::operator< ( y) const
inline

Less operator on an Accumulator and a number.

Definition at line 155 of file Accumulator.hpp.

template<typename T = Math::real>
bool GeographicLib::Accumulator< T >::operator<= ( y) const
inline

Less or equal operator on an Accumulator and a number.

Definition at line 159 of file Accumulator.hpp.

template<typename T = Math::real>
bool GeographicLib::Accumulator< T >::operator> ( y) const
inline

Greater operator on an Accumulator and a number.

Definition at line 163 of file Accumulator.hpp.

template<typename T = Math::real>
bool GeographicLib::Accumulator< T >::operator>= ( y) const
inline

Greater or equal operator on an Accumulator and a number.

Definition at line 167 of file Accumulator.hpp.


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