atan2d(3M)

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.

SEE ALSO

acosd(3M), asind(3M), atan2(3M), atand(3M), cosd(3M), sind(3M), tand(3M), math(5), values(5).