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+.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
+.TH "ATAN2" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
+.\" atan2 
+.SH NAME
+atan2, atan2f, atan2l \- arc tangent functions
+.SH SYNOPSIS
+.LP
+\fB#include <math.h>
+.br
+.sp
+double atan2(double\fP \fIy\fP\fB, double\fP \fIx\fP\fB);
+.br
+float atan2f(float\fP \fIy\fP\fB, float\fP \fIx\fP\fB);
+.br
+long double atan2l(long double\fP \fIy\fP\fB, long double\fP \fIx\fP\fB);
+.br
+\fP
+.SH DESCRIPTION
+.LP
+These functions shall compute the principal value of the arc tangent
+of \fIy\fP/ \fIx\fP, using the signs of both arguments to
+determine the quadrant of the return value.
+.LP
+An application wishing to check for error situations should set \fIerrno\fP
+to zero and call
+\fIfeclearexcept\fP(FE_ALL_EXCEPT) before calling these functions.
+On return, if \fIerrno\fP is non-zero or
+\fIfetestexcept\fP(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW)
+is non-zero, an error has occurred.
+.SH RETURN VALUE
+.LP
+Upon successful completion, these functions shall return the arc tangent
+of \fIy\fP/ \fIx\fP in the range [-pi,pi] radians.
+.LP
+If \fIy\fP is \(+-0 and \fIx\fP is < 0, \(+-pi shall be returned.
+.LP
+If \fIy\fP is \(+-0 and \fIx\fP is > 0, \(+-0 shall be returned.
+.LP
+If \fIy\fP is < 0 and \fIx\fP is \(+-0, -pi/2 shall be returned.
+.LP
+If \fIy\fP is > 0 and \fIx\fP is \(+-0, pi/2 shall be returned.
+.LP
+If \fIx\fP is 0, a pole error shall not occur.
+.LP
+If
+either \fIx\fP or \fIy\fP is NaN, a NaN shall be returned.
+.LP
+If the result underflows, a range error may occur and \fIy\fP/ \fIx\fP
+should be returned.
+.LP
+If \fIy\fP is \(+-0 and \fIx\fP is -0, \(+-pi shall be returned.
+.LP
+If \fIy\fP is \(+-0 and \fIx\fP is +0, \(+-0 shall be returned.
+.LP
+For finite values of \(+- \fIy\fP > 0, if \fIx\fP is -Inf, \(+-pi
+shall be
+returned.
+.LP
+For finite values of \(+- \fIy\fP > 0, if \fIx\fP is +Inf, \(+-0 shall
+be returned.
+.LP
+For finite values of \fIx\fP, if \fIy\fP is \(+-Inf, \(+-pi/2 shall
+be
+returned.
+.LP
+If \fIy\fP is \(+-Inf and \fIx\fP is -Inf, \(+-3pi/4 shall be returned.
+.LP
+If \fIy\fP is \(+-Inf and \fIx\fP is +Inf, \(+-pi/4 shall be returned.
+.LP
+If both arguments are 0, a domain error shall not occur. 
+.SH ERRORS
+.LP
+These functions may fail if:
+.TP 7
+Range\ Error
+The result underflows. 
+.LP
+If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
+then \fIerrno\fP shall be set to [ERANGE]. If the
+integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero,
+then the underflow floating-point exception shall be
+raised. 
+.sp
+.LP
+\fIThe following sections are informative.\fP
+.SH EXAMPLES
+.LP
+None.
+.SH APPLICATION USAGE
+.LP
+On error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling
+& MATH_ERREXCEPT) are independent of
+each other, but at least one of them must be non-zero.
+.SH RATIONALE
+.LP
+None.
+.SH FUTURE DIRECTIONS
+.LP
+None.
+.SH SEE ALSO
+.LP
+\fIatan\fP() , \fIfeclearexcept\fP() , \fIfetestexcept\fP() , \fIisnan\fP()
+, \fItan\fP() , the
+Base Definitions volume of IEEE\ Std\ 1003.1-2001, Section 4.18, Treatment
+of Error Conditions for Mathematical Functions, \fI<math.h>\fP
+.SH COPYRIGHT
+Portions of this text are reprinted and reproduced in electronic form
+from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
+-- Portable Operating System Interface (POSIX), The Open Group Base
+Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
+Electrical and Electronics Engineers, Inc and The Open Group. In the
+event of any discrepancy between this version and the original IEEE and
+The Open Group Standard, the original IEEE and The Open Group Standard
+is the referee document. The original Standard can be obtained online at
+http://www.opengroup.org/unix/online.html .