std::log(std::valarray)(3)

💖 NAME 💖

std::log(std::valarray) — literally std::log(std::valarray), bestie. This is the std::log(std::valarray)(3) page from the C++ Standard Libary manual, and we’re keeping all the facts periodt 💅✨

---

✨ Synopsis ✨

Okay so here’s the signature, no cap 🫶

Defined in header <valarray>
template< class T >
valarray<T> log( const valarray<T>& va );

For each element in va, it computes the natural logarithm of the value of the element. math but make it valarray 🌈

---

🌸 Parameters 🌸

• va — value array to apply the operation to 💖

---

💖 Return value 💖

A value array containing natural logarithms of the values in va. Iconic behavior, honestly 🎀

---

🧚 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. iykyk ✨

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.

Bestie, those replacement-type rules are giving very specific. Do not skip them 💀

---

🎀 Possible implementation 🎀

Here’s one possible implementation, cute and functional 🧚

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)
• log, logf, logl — computes natural (base e) logarithm (\({\small\ln{x}}\)ln(x)) (function) (C++11) (C++11)
• log(std::complex) — complex natural logarithm with the branch cuts along the negative real axis (function template)

---

🙈 Hidden category: 🙈

• Pages with unreviewed LWG DR marker

---

Signed, sealed, delivered: this is std::log(std::valarray)(3) from cppreference.com, dated 2024.06.10, and I’m obsessed 💅🫶✨