std::log(std::valarray)

 

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std::valarray

Member functions
valarray::valarray valarray::~valarray valarray::operator= valarray::operator[]   valarray::swap valarray::size valarray::resize valarray::sum valarray::min valarray::max valarray::shift valarray::cshift valarray::apply	valarray::operator+valarray::operator-valarray::operator~valarray::operator! valarray::operator+=valarray::operator-=valarray::operator*=valarray::operator/=valarray::operator%=valarray::operator&=valarray::operator|=valarray::operator^=valarray::operator<<=valarray::operator>>=
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swap (C++11) begin (C++11) end (C++11) abs exp log log10 pow sqrt sin cos tan asin acos atan atan2 sinh cosh tanh	operator*operator/operator%operator+operator-operator^operator&operator|operator<<operator>>operator&&operator|| operator==operator!=operator<operator>operator<=operator>=
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slice_array gslice_array indirect_array	slice gslice mask_array
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Defined in header <valarray>
template< class T > valarray<T> log( const valarray<T>& va );

For each element in va computes natural logarithm of the value of the element.

Parameters

va

-

value array to apply the operation to

Return value

Value array containing natural logarithms of the values in va.

Notes

Unqualified function (log) is used to perform the computation. If such function is not available, std::log is used due to argument-dependent lookup.

The function can be implemented with the return type different from std::valarray. In this case, the replacement type has the following properties:

• All const member functions of std::valarray are provided.
• std::valarray, std::slice_array, std::gslice_array, std::mask_array and std::indirect_array can be constructed from the replacement type.
• All functions accepting an argument of type const std::valarray& except begin() and end() (since C++11) should also accept the replacement type.
• All functions accepting two arguments of type const std::valarray& should accept every combination of const std::valarray& and the replacement type.
• The return type does not add more than two levels of template nesting over the most deeply-nested argument type.

Possible implementation

template< class T > valarray<T> log( const valarray<T>& va ) { valarray<T> other = va; for (T &i : other) { i = log(i); } return other; // proxy object may be returned }

Example

Run this code

#include <iomanip>
#include <iostream>
#include <valarray>
 
void show(char const* title, const std::valarray<double>& va)
{
    std::cout << title << " :" << std::right << std::fixed;
    for (double x : va) {
        std::cout << std::setw(10) << x;
    }
    std::cout << '\n';
}
 
int main()
{
    const std::valarray<double> n { 0.0, 1.0, 2.0, 3.0 };
    const std::valarray<double> exp_n { std::exp(n) };
    const std::valarray<double> log_exp_n { std::log(exp_n) };
 
    show("n      ", n);
    show("eⁿ     ", exp_n);
    show("log(eⁿ)", log_exp_n);
}

Output:

n       :  0.000000  1.000000  2.000000  3.000000
eⁿ      :  1.000000  2.718282  7.389056 20.085537
log(eⁿ) :  0.000000  1.000000  2.000000  3.000000

See also

log10(std::valarray)	applies the function std::log10 to each element of valarray (function template)
exp(std::valarray)	applies the function std::exp to each element of valarray (function template)
loglogflogl (C++11)(C++11)	computes natural (base e) logarithm (\({\small \ln{x} }\)ln(x)) (function)
log(std::complex)	complex natural logarithm with the branch cuts along the negative real axis (function template)