> ## Name

> atan - returns arctangent of scalars and vectors.

> ## Synopsis

>     float  atan(float a);
>     float1 atan(float1 a);
>     float2 atan(float2 a);
>     float3 atan(float3 a);
>     float4 atan(float4 a);

>     half   atan(half a);
>     half1  atan(half1 a);
>     half2  atan(half2 a);
>     half3  atan(half3 a);
>     half4  atan(half4 a);

>     fixed  atan(fixed a);
>     fixed1 atan(fixed1 a);
>     fixed2 atan(fixed2 a);
>     fixed3 atan(fixed3 a);
>     fixed4 atan(fixed4 a);

> ## Parameters

> a
>   Vector or scalar of which to determine the arctangent.

> ## Description

> Returns the arctangent of x in the range of -pi/2 to pi/2 radians.

> For vectors, the returned vector contains the arctangent of each element of the input vector.

> ## Reference Implementation

> atan for a float scalar could be implemented like this.

>     float atan(float x) {
>         return atan2(x, float(1));
>     }

> atan2 is typically implemented as an approximation.

> ## Profile Support

> atan is supported in all profiles but fp20.

> ## See Also

> abs, acos, asin, atan2. sqrt, tan