std::log(std::valarray)
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std::valarray
Defined in header
<valarray>
template< class T >
valarray<T> log( const valarray<T>& va );
valarray<T> log( const valarray<T>& va );
For each element in va computes natural logarithm of the value of the element.
[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:
- 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.
- For every function taking a const std::valarray <T>& except begin() and end() (since C++11), identical functions taking the replacement types shall be added;
- For every function taking two const std::valarray <T>& arguments, identical functions taking every combination of const std::valarray <T>& and replacement types shall be added.
- The return type does not add more than two levels of template nesting over the most deeply-nested argument type.
[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; // proxy object may be returned }
[edit] 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
[edit] See also
complex natural logarithm with the branch cuts along the negative real axis
(function template) [edit]
(function template) [edit]
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