atan

atan

Compute the Trigonometric Arc Tangent

Portability: ISO/ANSI C conforming, UNIX compatible

SYNOPSIS
DESCRIPTION
RETURN VALUE
DIAGNOSTICS
EXAMPLE
RELATED FUNCTIONS
SEE ALSO

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:

[IMAGE]

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) = %f\n", value, pival);
}

RELATED FUNCTIONS

acos , asin , atan2 , _matherr

SEE ALSO

Mathematical Functions

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