SAS/C Library Reference, Vol. 1

asin -- Compute the Trigonometric Arc Sine

SYNOPSIS

 #include <math.h>

 double asin(double x);

DESCRIPTION

asin computes the trigonometric arc sine of the value x. The arc sine function is the inverse of the sine function and is expressed by the following relation:

 r = arcsin (x)

x is in the closed interval [ - 1.0,1.0].

RETURN VALUE

asin returns the principal value of the arc sine of the argument x, provided that this value is defined and computable. The return value is a double precision floating-point number in the closed interval [-pi/2, pi/2] radians.

DIAGNOSTICS

asin returns 0.0 if the value of its argument is larger than 1.0 or smaller than - 1.0. The run-time library writes an error message to the standard error file (stderr) in this case.

If an error occurs in asin, the _matherr routine is called. You can supply your own version of _matherr to suppress the diagnostic message or modify the value returned.

EXAMPLE

This example computes pi as 4 times the arc sine of the square root of 0.5:

  #include <math.h>
  #include <stdio.h>

  main()
  {
     double pival, value;
     value = .500;

     pival = 4 * asin(sqrt(value));
     printf("4 * asin(sqrt(%f)) = %fn",value,pival);
  }

RELATED FUNCTIONS

acos, atan, _matherr