gum::GammaLog2 Class Reference

The class for computing Log2 (Gamma(x)) More...

#include <agrum/core/math/gammaLog2.h>

Collaboration diagram for gum::GammaLog2:

Public Member Functions
Constructors / Destructors
	GammaLog2 (bool requires_precision=false)
	Default constructor. More...
	GammaLog2 (const GammaLog2 &from)
	Copy constructor. More...
	GammaLog2 (GammaLog2 &&from)
	Move constructor. More...
	~GammaLog2 ()
	Class destructor. More...
Operators
double	operator() (double x) const
	Returns log2 ( gamma (x) ) for x > 0. More...
void	setPrecision (bool p)
	Sets whether we need more precision for small values. More...
double	gammaLog2 (double x) const
	Returns log2 ( gamma (x) ) for x >= 0. More...

Detailed Description

The class for computing Log2 (Gamma(x))

Definition at line 45 of file gammaLog2.h.

Constructor & Destructor Documentation

GammaLog2() [1/3]

gum::GammaLog2::GammaLog2

(

bool

requires_precision = false

)

Default constructor.

Parameters

requires_precision

Set if precision is required or not.

Definition at line 36 of file gammaLog2.cpp.

                                              :
      __requires_precision{requires_precision} {
    GUM_CONSTRUCTOR(GammaLog2);
  }

GammaLog2() [2/3]

gum::GammaLog2::GammaLog2

(

const GammaLog2 &

from

)

Copy constructor.

Parameters

from	The gum::GammaLog2 to copy.

Definition at line 42 of file gammaLog2.cpp.

References __requires_precision.

                                            :
      __requires_precision{from.__requires_precision} {
    GUM_CONS_CPY(GammaLog2);
  }

GammaLog2() [3/3]

gum::GammaLog2::GammaLog2

(

GammaLog2 &&

from

)

Move constructor.

Parameters

from	The gum::GammaLog2 to move.

Definition at line 48 of file gammaLog2.cpp.

                                       :
      __requires_precision{from.__requires_precision} {
    GUM_CONS_MOV(GammaLog2);
  }

~GammaLog2()

gum::GammaLog2::~GammaLog2

(

)

Class destructor.

Definition at line 54 of file gammaLog2.cpp.

References __small_values.

{ GUM_DESTRUCTOR(GammaLog2); }

Member Function Documentation

gammaLog2()

ALWAYS_INLINE double gum::GammaLog2::gammaLog2

(

double

x

)

const

Returns log2 ( gamma (x) ) for x >= 0.

Parameters

x	A positive double.

Returns

Returns log2 ( gamma (x) ) for x >= 0.

Exceptions

OutOfBounds

Raised if x <= 0.

Definition at line 29 of file gammaLog2_inl.h.

References __1log2, __log_sqrt_2pi, __requires_precision, __small_values, and GUM_ERROR.

Referenced by operator()().

                                                          {
    if (x <= 0)
      GUM_ERROR(OutOfBounds,
                "log2(gamma()) should be called with a positive argument");

    // if x is small, use precomputed values
    if (x < 50) {
      if (__requires_precision) {
        Idx index = int(x * 100);
        return __small_values[index]
               + (__small_values[index + 1] - __small_values[index])
                    * double(x * 100 - index);
      } else {
        Idx index = int(x * 100 + 0.5);
        return __small_values[index];
      }
    }

    // returns the approximation by the stirling formula
    return (__log_sqrt_2pi + (x - 0.5f) * log(x) - x + log(1.0 + 1.0 / (12 * x)))
           * __1log2;
  }

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operator()()

ALWAYS_INLINE double gum::GammaLog2::operator()

(

double

x

)

const

Returns log2 ( gamma (x) ) for x > 0.

Exceptions

OutOfBounds

Raised if raised if x <= 0.

Definition at line 52 of file gammaLog2_inl.h.

References gammaLog2().

                                                           {
    return gammaLog2(x);
  }

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setPrecision()

INLINE void gum::GammaLog2::setPrecision

(

bool

p

)

Sets whether we need more precision for small values.

Parameters

p	If true, precision is enable.

Definition at line 56 of file gammaLog2_inl.h.

References __requires_precision.

{ __requires_precision = prec; }

Member Data Documentation

__1log2

constexpr double gum::GammaLog2::__1log2 {M_LOG2E}

staticprivate

The value of 1 / std::log(2).

Definition at line 114 of file gammaLog2.h.

Referenced by gammaLog2().

__log_sqrt_2pi

constexpr double gum::GammaLog2::__log_sqrt_2pi {GUM_LOG_SQRT_2PI}

staticprivate

The value of std::log ( std::sqrt(2pi) ).

Definition at line 117 of file gammaLog2.h.

Referenced by gammaLog2().

__requires_precision

bool gum::GammaLog2::__requires_precision {false}

private

Indicates whether we need more precision for small values.

Definition at line 111 of file gammaLog2.h.

Referenced by GammaLog2(), gammaLog2(), and setPrecision().

__small_values

const std::vector< double > gum::GammaLog2::__small_values

staticprivate

The 5000 values from 0 to 50 by step of 1/100.

Definition at line 120 of file gammaLog2.h.

Referenced by gammaLog2(), and ~GammaLog2().

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

• agrum/core/math/gammaLog2.h
• agrum/core/math/gammaLog2.cpp
• agrum/core/math/gammaLog2_inl.h