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# atan2 (<valarray>)

Visual Studio 2012

Returns a valarray whose elements are equal to the arctangent of the Cartesian components specified by a combination of constants and elements of valarrays.

```template<class Type>
valarray<Type> atan2(
const valarray<Type>& _Left,
const valarray<Type>& _Right
);
template<class Type>
valarray<Type> atan2(
const valarray<Type> _Left,
const Type& _Right
);
template<class Type>
valarray<Type> atan2(
const Type& _Left,
const valarray<Type>& _Right
);
```
_Left

The constant numerical data type or input valarray whose elements provide the values for the y-coordinate of the arctangent argument.

_Right

The constant numerical data type or input valarray whose elements provide the values for the x-coordinate of the arctangent argument.

A valarray whose elements I are equal to the arctangent of:

• _Left [ I ] / _Right [ I ] for the first template function.

• _Left [ I ] / _Right for the second template function.

• _Left / _Right [ I ] for the third template function.

The units of the returned elements are in radians.

This function preserves information about the signs of the components in the argument that is lost by the standard tangent function, and this knowledge of the quadrant enables the return value to be assigned a unique angle between +pi and –pi.

If _Left and _Right have a different number of elements, the result is undefined.

```// valarray_atan2.cpp
// compile with: /EHsc
#include <valarray>
#include <iostream>
#include <iomanip>

int main( )
{
using namespace std;
double pi = 3.14159265359;
int i;

valarray<double> va1y ( 1 , 4 ), va1x ( 1 , 4 );
va1x [ 1 ] = -1;
va1x [ 2 ] = -1;
va1y [ 2 ] = -1;
va1y [ 3 ] = -1;
valarray<double> va2 ( 4 );

cout << "The initial valarray for the x coordinate is: ( ";
for ( i = 0 ; i < 4 ; i++ )
cout << va1x [ i ] << " ";
cout << ")." << endl;

cout << "The initial valarray for the y coordinate is: ( ";
for ( i = 0 ; i < 4 ; i++ )
cout << va1y [ i ] << " ";
cout << ")." << endl;

va2 = atan2 ( va1y , va1x );
cout << "The atan2 ( y / x ) of the initial valarrays is:\n";
for ( i = 0 ; i < 4 ; i++ )
cout << setw( 10 ) << va2 [ i ]
<< "  radians, which is  "
<< setw( 11 ) << ( 180/pi ) * va2 [ i ]
<< "degrees" << endl;
cout << endl;
}
```
```The initial valarray for the x coordinate is: ( 1 -1 -1 1 ).
The initial valarray for the y coordinate is: ( 1 1 -1 -1 ).
The atan2 ( y / x ) of the initial valarrays is: