Sun Microsystems, Inc. gratefully acknowledges The Open Group for

permission to reproduce portions of its copyrighted documentation.

Original documentation from The Open Group can be obtained online at

http://www.opengroup.org/bookstore/.

The Institute of Electrical and Electronics Engineers and The Open

Group, have given us permission to reprint portions of their

documentation.

In the following statement, the phrase ``this text'' refers to portions

of the system documentation.

Portions of this text are reprinted and reproduced in electronic form

in the SunOS Reference Manual, from IEEE Std 1003.1, 2004 Edition,

Standard for Information Technology -- Portable Operating System

Interface (POSIX), The Open Group Base Specifications Issue 6,

Copyright (C) 2001-2004 by the Institute of Electrical and Electronics

Engineers, Inc and The Open Group. In the event of any discrepancy

between these versions 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.

This notice shall appear on any product containing this material.

The contents of this file are subject to the terms of the

Common Development and Distribution License (the "License").

You may not use this file except in compliance with the License.

You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE

or http://www.opensolaris.org/os/licensing.

See the License for the specific language governing permissions

and limitations under the License.

When distributing Covered Code, include this CDDL HEADER in each

file and include the License file at usr/src/OPENSOLARIS.LICENSE.

If applicable, add the following below this CDDL HEADER, with the

fields enclosed by brackets "[]" replaced with your own identifying

information: Portions Copyright [yyyy] [name of copyright owner]

Copyright (c) 1992, X/Open Company Limited. All Rights Reserved.

Copyright (c) 2001, The IEEE and The Open Group. All Rights Reserved.

Portions Copyright (c) 2006, Sun Microsystems, Inc. All Rights Reserved.

c99 [ flag... ] file... -lm [ library... ] #include <math.h> double atan2(double y, double x);

float atan2f(float y, float x);

long double atan2l(long double y, long double x);

These functions compute the principal value of the arc tangent of y/x, using the signs of both arguments to determine the quadrant of the return value.

Upon successful completion, these functions return the arc tangent of y/x in the range [ -\c \c ,\c \c ] radians.

If y is \(+-0 and x is < 0, \(+-\c \c is returned.

If y is \(+-0 and x is > 0, \(+-0 is returned.

If y is < 0 and x is \(+-0, -\c \c /2 is returned.

If y is > 0 and x is \(+-0, \c \c /2 is returned.

If x is 0, a pole error does not occur.

If either x or y is NaN, a NaN is returned.

If y is \(+-0 and x is -0, \(+-\c \c is returned.

If y is \(+-0 and x is +0, \(+-0 is returned.

For finite values of \(+-y > 0, if x is -Inf, \(+-\c \c is returned.

For finite values of \(+-y > 0, if x is +Inf, \(+-0 is returned.

For finite values of x, if y is \(+-Inf, \(+-\c \c /2 is returned.

If y is \(+-Inf and x is -Inf, \(+-3\c \c /4 is returned.

If y is \(+-Inf and x is +Inf, \(+-\c \c /4 is returned.

If both arguments are 0, a domain error does not occur.

No errors are defined.

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPE ATTRIBUTE VALUE |

Interface Stability Standard |

MT-Level MT-Safe |

atan(3M), isnan(3M), math.h(3HEAD), tan(3M), attributes(5), standards(5)