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std::log(std::valarray)

From cppreference.com
< cpp‎ | numeric‎ | valarray
 
 
 
 
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.

Contents

[edit] Parameters

va - value array to apply the operation to

[edit] Return value

Value array containing natural logarithms of the values in va.

[edit] 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:

[edit] 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;
}

[edit] Example

#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

[edit] See also

applies the function std::log10 to each element of valarray
(function template) [edit]
applies the function std::exp to each element of valarray
(function template) [edit]
(C++11)(C++11)
computes natural (base e) logarithm (ln(x))
(function) [edit]
complex natural logarithm with the branch cuts along the negative real axis
(function template) [edit]