# std::atan2(std::valarray) (3) - Linux Man Pages

## NAME

std::atan2(std::valarray) - std::atan2(std::valarray)

## Synopsis

template< class T > (1)
std::valarray<T> atan2( const std::valarray<T>& y, const std::valarray<T>& x );
template< class T >
std::valarray<T> atan2( const std::valarray<T>& y, (2)
const typename std::valarray<T>::value_type& vx );
template< class T >
std::valarray<T> atan2( const typename std::valarray<T>::value_type& vy, (3)
const std::valarray<T>& x );

Computes the inverse tangent of y/x using the signs of arguments to correctly determine quadrant.
1) Computes the inverse tangent of each pair of corresponding values from y and x.
The behavior is undefined if x.size() != y.size().
2) Computes the inverse tangent of vx and each value in the numeric array y.
3) Computes the inverse tangent of vy and each value in the numeric array x.

## Parameters

x, y - numeric arrays to compute inverse tangent of
vy, vx - values to compute inverse tangent of

## Return value

A numeric array containing the results of computation of inverse tangent.

## Notes

Unqualified function (atan2) is used to perform the computation. If such function is not available, std::atan2 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.

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG_3074 C++98 T is deduced from both the scalar and the valarray for (2-3), disallowing mixed-type calls only deduce T from the valarray

## Example

This section is incomplete
Reason: no example

applies the function std::asin to each element of valarray
asin(std::valarray) (function template)
applies the function std::acos to each element of valarray
acos(std::valarray) (function template)
applies the function std::atan to each element of valarray
atan(std::valarray) (function template)

atan2
atan2f
atan2l arc tangent, using signs to determine quadrants
(function)

(C++11)
(C++11)
returns the phase angle
arg (function template)