SAS/C Library Reference, Vol. 1

atan -- Compute the Trigonometric Arc Tangent

SYNOPSIS

 #include <math.h>

 double atan(double x);

DESCRIPTION

atan computes the trigonometric arc tangent of its argument x. The arc tangent is the inverse of the tangent function and is expressed by the following relation:

 r = arctan (x)

RETURN VALUE

atan returns the principal value of the arc tangent of the argument x, provided that this value is defined and computable. The return value is a double-precision, floating-point number in the open interval (-pi/2, pi/2) radians.

DIAGNOSTICS

If an error occurs in atan, 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 tangent of 1:

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

  main()
  {
     double pival, value;
     value = 1.000;

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

RELATED FUNCTIONS

acos, asin, atan2, _matherr