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<BLOCKQUOTE>
<H1><A NAME="NAME"><A NAME="1">NAME
</A></A></H1>
<P>
<B>atan2</B> - returns arctangent of scalars and vectors.
</P>
<H1><A NAME="SYNOPSIS"><A NAME="2">SYNOPSIS
</A></A></H1>
<PRE> float atan2(float y, float x);
float1 atan2(float1 y, float1 x);
float2 atan2(float2 y, float2 x);
float3 atan2(float3 y, float3 x);
float4 atan2(float4 y, float4 x);
half atan2(half y, half x);
half1 atan2(half1 y, half1 x);
half2 atan2(half2 y, half2 x);
half3 atan2(half3 y, half3 x);
half4 atan2(half4 y, half4 x);
fixed atan2(fixed y, fixed x);
fixed1 atan2(fixed1 y, fixed1 x);
fixed2 atan2(fixed2 y, fixed2 x);
fixed3 atan2(fixed3 y, fixed3 x);
fixed4 atan2(fixed4 y, fixed4 x);
</PRE>
<H1><A NAME="PARAMETERS"><A NAME="3">PARAMETERS
</A></A></H1>
<DL>
<DT><STRONG>y
</STRONG></DT>
<DD>
<P>
Vector or scalar for numerator of ratio of which to determine the arctangent.
</P>
<DT><STRONG>x
</STRONG></DT>
<DD>
<P>
Vector or scalar of denominator of ratio of which to determine the arctangent.
</P>
</DD></DL>
<H1><A NAME="DESCRIPTION"><A NAME="4">DESCRIPTION
</A></A></H1>
<P>
<B>atan2</B> calculates the arctangent of y/x. <B>atan2</B> is well defined for every point other than the origin, even if x equals 0 and y does not equal 0.
</P>
<P>
For vectors, the returned vector contains the arctangent of each
element of the input vector.
</P>
<H1><A NAME="REFERENCE_IMPLEMENTATION"><A NAME="5">REFERENCE IMPLEMENTATION
</A></A></H1>
<P>
<B>atan2</B> for a <B>float2</B> scalar could be implemented as an approximation like this.
</P>
<PRE> float2 atan2(float2 y, float2 x)
{
float2 t0, t1, t2, t3, t4;
t3 = abs(x);
t1 = abs(y);
t0 = max(t3, t1);
t1 = min(t3, t1);
t3 = float(1) / t0;
t3 = t1 * t3;
t4 = t3 * t3;
t0 = - float(0.013480470);
t0 = t0 * t4 + float(0.057477314);
t0 = t0 * t4 - float(0.121239071);
t0 = t0 * t4 + float(0.195635925);
t0 = t0 * t4 - float(0.332994597);
t0 = t0 * t4 + float(0.999995630);
t3 = t0 * t3;
t3 = (abs(y) > abs(x)) ? float(1.570796327) - t3 : t3;
t3 = (x < 0) ? float(3.141592654) - t3 : t3;
t3 = (y < 0) ? -t3 : t3;
return t3;
}
</PRE>
<H1><A NAME="PROFILE_SUPPORT"><A NAME="6">PROFILE SUPPORT
</A></A></H1>
<P>
<B>atan2</B> is supported in all profiles but <A HREF="fp20.html">fp20</A>.
</P>
<H1><A NAME="SEE_ALSO"><A NAME="7">SEE ALSO
</A></A></H1>
<P>
<A HREF="abs.html"><I>abs</I></A>, <A HREF="acos.html"><I>acos</I></A>, <A HREF="asin.html"><I>asin</I></A>, <A HREF="atan.html"><I>atan</I></A>. <A HREF="sqrt.html"><I>sqrt</I></A>, <A HREF="tan.html"><I>tan</I></A>
</P>
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