HP-UX Reference (11i v1 05/09) - 3 Library Functions A-M (vol 6)

ManualsBrandsHP ManualsSoftwareHP-UX Reference Manuals

atan2d(3M) atan2d(3M)

NAME

atan2d( ), atan2df( ) - degree-valued arctangent-and-quadrant functions

SYNOPSIS

#include <math.h>

double atan2d(double y, double x);

float atan2df(float y, float x);

DESCRIPTION

atan2d() is a degree-valued version of the

atan2() function. It returns the arctangent of y/x, in the

range −180 to 180, using the signs of both arguments to determine the quadrant of the return value.

atan2df() is a float version of atan2d()

; it takes float arguments and returns a float result.

atan2d() and atan2df() are not speciﬁed by any standard, but

atan2df() is named in accordance

with the conventions speciﬁed in the "Future Library Directions" section of the ANSI C standard.

To use these functions, compile either with the default

-Ae option or with the -Aa and

-D_HPUX_SOURCE options. Make sure your program includes <

math.h>. Link in the math library by

specifying

-lm on the compiler or linker command line.

RETURN VALUE

If y and x are +INFINITY, atan2d()

returns 45.

If y is +INFINITY and x is −INFINITY,

atan2d() returns 135.

If y is −INFINITY and x is +INFINITY,

atan2d() returns −45.

If y and x are −INFINITY,

atan2d()

returns −135.

If y is zero and x is greater than zero,

atan2d() returns zero.

If y is zero and x is less than zero, atan2d() returns 180.

If y is −zero and x is less than zero, atan2d() returns −180.

If y is greater than zero and x is zero,

atan2d() returns 90.

If y is less than zero and x is zero, atan2d() returns −90.

If y/x would overﬂow, atan2d() returns ±90. The result will be 90 if y is greater than zero and −90 if y is

less than zero.

If y/x after rounding would be smaller in magnitude than

MINDOUBLE, atan2d() returns ±180 or zero.

The result will be zero if x is greater than zero, 180 if x is less than zero and y is greater than zero, and

−180 if x and y are both less than zero.

If both x and y are zero,

atan2d() returns NaN.

If x or y is NaN, atan2d() returns NaN.

If the correct value after rounding would be smaller in magnitude than MINDOUBLE , atan2d() returns

zero.

ERRORS

No errors are deﬁned.