std::log10(std::valarray)

template< class T >
valarray<T> log10( const valarray<T>& va );

For each element in va computes common (base 10) logarithm of the value of the element.

Parameters

Return value

Value array containing common logarithms of the values in va.

Notes

Unqualified function (log10) is used to perform the computation. If such function is not available, std::log10 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> log10( const valarray<T>& va )
{
    valarray<T> other = va;
    for (T &i : other)
        i = log10(i);
 
    return other; // proxy object may be returned
}

Example

#include <cmath>
#include <iomanip>
#include <iostream>
#include <valarray>
 
void show(char const* title, const std::valarray<float>& va)
{
    std::cout << title << " : " << std::right;
    for (float x : va) {
        std::cout << std::setw(6) << x;
    }
    std::cout << '\n';
}
 
int main()
{
    const std::valarray<float> n { -2.f, -1.f, 0.f, 1.f, 2.f, 3.f, INFINITY };
    const std::valarray<float> pow10 { std::pow(10.f, n) };
    const std::valarray<float> log10_pow10 { std::log10(pow10) };
 
    show("n      ", n);
    show("10ⁿ    ", pow10);
    show("lg(10ⁿ)", log10_pow10);
}

n       :     -2    -1     0     1     2     3   inf
10ⁿ     :   0.01   0.1     1    10   100  1000   inf
lg(10ⁿ) :     -2    -1     0     1     2     3   inf

See also