Technical Reference: Base Operating System and Extensions, Volume 1

asin, asinl, acos, acosl, atan, atanl, atan2, or atan2l Subroutine

Purpose

Computes inverse trigonometric functions.

Libraries

IEEE Math Library (libm.a)
or System V Math Library (libmsaa.a)

Syntax

double asin ( x) double x;

long double asinl (x)
long double x;

double acos (x)
double x;

long double acosl (x)
long double x;

double atan (x)
double x;

long double atanl (x)
long double x;

double atan2 ( y, x) double y, x;

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

Description

The asin and asinl subroutines return the principal value of the arc sine of x, in the range [-pi/2, pi/2].

The acos and acosl subroutines return the principal value of the arc cosine of x, in the range [0, pi].

The atan and atanl subroutines return the principal value of the arc tangent of x, in the range [-pi/2, pi/2].

The atan2 and atan2l subroutines return the principal value of the arc tangent of y/x, using the signs of both parameters to determine the quadrant of the return value. The return values are in the range [-pi, pi].

Parameters

x	Specifies a double-precision floating-point value. For the asinl, acosl, atanl, and atan2l subroutines, specifies a long double-precision floating-point value.
y	Specifies a double-precision floating-point value. For the asinl, acosl, atanl, and atan2l subroutines, specifies long double-precision floating-point value.

Error Codes

When using the libm.a (-lm) library:

asin, asinl, acos, acosl

Return a NaNQ and set the errno global variable to EDOM if the absolute value of the parameter is greater than 1.

When using libmsaa.a (-lmsaa):

asin, acos, atan2,	If the absolute value of the parameter of asin or acos is greater than 1, or if both parameters of atan2 are 0, then 0 is returned and errno is set to EDOM. In addition, a message indicating DOMAIN error is printed on the standard output.
asinl, acosl, atan2l	Return a NaNQ and set the errno global variable to EDOM if the absolute value of the parameter is greater than 1.

These error-handling procedures may be changed with the matherr subroutine when using the libmsaa.a (-lmsaa) library.

Implementation Specifics

These subroutines are part of Base Operating System (BOS) Runtime.

Related Information

The asinh, acosh, or atanh (asinh, acosh, or atanh Subroutine) subroutine, matherr (matherr Subroutine) subroutine.

Subroutines Overview in AIX 5L Version 5.1 General Programming Concepts: Writing and Debugging Programs.

128-Bit long double Floating-Point Format in AIX 5L Version 5.1 General Programming Concepts: Writing and Debugging Programs.