2004-11-03 13:51:07 +00:00
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.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
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2007-06-20 22:33:04 +00:00
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.TH "ATAN2" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
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2004-11-03 13:51:07 +00:00
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.\" atan2
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2007-09-20 06:03:25 +00:00
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.SH PROLOG
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This manual page is part of the POSIX Programmer's Manual.
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The Linux implementation of this interface may differ (consult
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the corresponding Linux manual page for details of Linux behavior),
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or the interface may not be implemented on Linux.
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2004-11-03 13:51:07 +00:00
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.SH NAME
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atan2, atan2f, atan2l \- arc tangent functions
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.SH SYNOPSIS
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.LP
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\fB#include <math.h>
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.br
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.sp
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double atan2(double\fP \fIy\fP\fB, double\fP \fIx\fP\fB);
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.br
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float atan2f(float\fP \fIy\fP\fB, float\fP \fIx\fP\fB);
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.br
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long double atan2l(long double\fP \fIy\fP\fB, long double\fP \fIx\fP\fB);
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.br
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\fP
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.SH DESCRIPTION
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.LP
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These functions shall compute the principal value of the arc tangent
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of \fIy\fP/ \fIx\fP, using the signs of both arguments to
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determine the quadrant of the return value.
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.LP
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An application wishing to check for error situations should set \fIerrno\fP
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to zero and call
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\fIfeclearexcept\fP(FE_ALL_EXCEPT) before calling these functions.
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On return, if \fIerrno\fP is non-zero or
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\fIfetestexcept\fP(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW)
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is non-zero, an error has occurred.
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.SH RETURN VALUE
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.LP
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Upon successful completion, these functions shall return the arc tangent
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of \fIy\fP/ \fIx\fP in the range [-pi,pi] radians.
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.LP
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If \fIy\fP is \(+-0 and \fIx\fP is < 0, \(+-pi shall be returned.
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.LP
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If \fIy\fP is \(+-0 and \fIx\fP is > 0, \(+-0 shall be returned.
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.LP
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If \fIy\fP is < 0 and \fIx\fP is \(+-0, -pi/2 shall be returned.
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.LP
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If \fIy\fP is > 0 and \fIx\fP is \(+-0, pi/2 shall be returned.
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.LP
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If \fIx\fP is 0, a pole error shall not occur.
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.LP
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If
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either \fIx\fP or \fIy\fP is NaN, a NaN shall be returned.
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.LP
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If the result underflows, a range error may occur and \fIy\fP/ \fIx\fP
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should be returned.
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.LP
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If \fIy\fP is \(+-0 and \fIx\fP is -0, \(+-pi shall be returned.
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.LP
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If \fIy\fP is \(+-0 and \fIx\fP is +0, \(+-0 shall be returned.
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.LP
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For finite values of \(+- \fIy\fP > 0, if \fIx\fP is -Inf, \(+-pi
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shall be
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returned.
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.LP
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For finite values of \(+- \fIy\fP > 0, if \fIx\fP is +Inf, \(+-0 shall
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be returned.
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.LP
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For finite values of \fIx\fP, if \fIy\fP is \(+-Inf, \(+-pi/2 shall
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be
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returned.
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.LP
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If \fIy\fP is \(+-Inf and \fIx\fP is -Inf, \(+-3pi/4 shall be returned.
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.LP
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If \fIy\fP is \(+-Inf and \fIx\fP is +Inf, \(+-pi/4 shall be returned.
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.LP
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If both arguments are 0, a domain error shall not occur.
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.SH ERRORS
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.LP
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These functions may fail if:
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.TP 7
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Range\ Error
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The result underflows.
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.LP
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If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
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then \fIerrno\fP shall be set to [ERANGE]. If the
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integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero,
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then the underflow floating-point exception shall be
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raised.
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.sp
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.LP
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\fIThe following sections are informative.\fP
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.SH EXAMPLES
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.LP
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None.
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.SH APPLICATION USAGE
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.LP
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On error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling
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& MATH_ERREXCEPT) are independent of
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each other, but at least one of them must be non-zero.
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.SH RATIONALE
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.LP
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None.
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.SH FUTURE DIRECTIONS
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.LP
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None.
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.SH SEE ALSO
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.LP
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2007-09-20 06:11:55 +00:00
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\fIatan\fP(), \fIfeclearexcept\fP(), \fIfetestexcept\fP(), \fIisnan\fP()
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, \fItan\fP(), the
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2004-11-03 13:51:07 +00:00
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Base Definitions volume of IEEE\ Std\ 1003.1-2001, Section 4.18, Treatment
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of Error Conditions for Mathematical Functions, \fI<math.h>\fP
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.SH COPYRIGHT
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Portions of this text are reprinted and reproduced in electronic form
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from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
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-- Portable Operating System Interface (POSIX), The Open Group Base
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Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
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Electrical and Electronics Engineers, Inc and The Open Group. In the
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event of any discrepancy between this version and the original IEEE and
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The Open Group Standard, the original IEEE and The Open Group Standard
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is the referee document. The original Standard can be obtained online at
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http://www.opengroup.org/unix/online.html .
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