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# atan (<valarray>)

Visual Studio 2013

Operates on the elements of an input valarray, returning a valarray whose elements are equal to the principal value of the arctangent of the elements of the input valarray.

```template<class Type>
valarray<Type> atan(
const valarray<Type>& _Left
);
```

## Parameters

_Left

The input valarray whose elements are to be operated on by the member function.

## Return Value

A valarray whose elements are equal to the arctangent of the elements of the input valarray.

## Remarks

The units of the returned elements are in radians.

The return value is a principal value between +pi/2 and –pi/2 that is consistent with the tangent value input.

## Example

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

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

valarray<double> va1 ( 9 );
va1 [ 0 ] = -100;
for ( i = 1 ; i < 8 ; i++ )
va1 [ i ] =  5 * ( 0.25 * i - 1 );
va1 [ 8 ] = 100;
valarray<double> va2 ( 9 );

cout << "The initial valarray is: ";
for ( i = 0 ; i < 9 ; i++ )
cout << va1 [ i ] << " ";
cout << "." << endl;

va2 = atan ( va1 );
cout << "The arcsine of the initial valarray is:\n";
for ( i = 0 ; i < 9 ; i++ )
cout << setw(10) << va2 [ i ]
<< "  radians, which is  "
<< setw(11) << (180/pi) * va2 [ i ]
<< "  degrees" << endl;
cout << endl;
}
```
```The initial valarray is: -100 -3.75 -2.5 -1.25 0 1.25 2.5 3.75 100 .
The arcsine of the initial valarray is:
-1.5608  radians, which is     -89.4271  degrees
-1.31019  radians, which is     -75.0686  degrees
-1.19029  radians, which is     -68.1986  degrees
-0.896055  radians, which is     -51.3402  degrees
0  radians, which is            0  degrees
0.896055  radians, which is      51.3402  degrees
1.19029  radians, which is      68.1986  degrees
1.31019  radians, which is      75.0686  degrees
1.5608  radians, which is      89.4271  degrees```