Difference between revisions of "cpp/numeric/valarray/log"
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{{cpp/title|log{{small|(std::valarray)}}}} | {{cpp/title|log{{small|(std::valarray)}}}} | ||
{{cpp/numeric/valarray/navbar}} | {{cpp/numeric/valarray/navbar}} | ||
| − | {{ddcl | header=valarray | 1= | + | {{ddcl|header=valarray|1= |
template< class T > | template< class T > | ||
valarray<T> log( const valarray<T>& va ); | valarray<T> log( const valarray<T>& va ); | ||
}} | }} | ||
| − | For each element in {{ | + | For each element in {{c|va}} computes natural logarithm of the value of the element. |
===Parameters=== | ===Parameters=== | ||
| − | {{ | + | {{par begin}} |
| − | {{ | + | {{par|va|value array to apply the operation to}} |
| − | {{ | + | {{par end}} |
===Return value=== | ===Return value=== | ||
| − | Value array natural logarithms of the values in {{ | + | Value array containing natural logarithms of the values in {{c|va}}. |
===Notes=== | ===Notes=== | ||
| Line 22: | Line 22: | ||
===Possible implementation=== | ===Possible implementation=== | ||
| − | {{ | + | {{cpp/numeric/valarray/impl|log}} |
| − | + | ||
| − | + | ||
| − | + | ||
| − | + | ||
| − | + | ||
| − | + | ||
| − | + | ||
| − | + | ||
| − | }} | + | |
===Example=== | ===Example=== | ||
{{example | {{example | ||
|code= | |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= | |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=== | ||
| + | {{dsc begin}} | ||
| + | {{dsc inc|cpp/numeric/valarray/dsc log10}} | ||
| + | {{dsc inc|cpp/numeric/valarray/dsc exp}} | ||
| + | {{dsc inc|cpp/numeric/math/dsc log}} | ||
| + | {{dsc inc|cpp/numeric/complex/dsc log}} | ||
| + | {{dsc end}} | ||
| + | |||
| + | {{langlinks|de|es|fr|it|ja|pt|ru|zh}} | ||
Latest revision as of 01:50, 17 October 2023
| Defined in header <valarray>
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| template< class T > valarray<T> log( const valarray<T>& va ); |
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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:
- 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
| applies the function std::log10 to each element of valarray (function template) | |
| applies the function std::exp to each element of valarray (function template) | |
| (C++11)(C++11) |
computes natural (base e) logarithm (ln(x)) (function) |
| complex natural logarithm with the branch cuts along the negative real axis (function template) |
