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atan

Arc tangent function of one variable

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Contents

Interface
Description
Special Values
See Also
Standards
Compatibility
Page Comments

Interface

#include <math.h>

	double	`atan` (double x)
	long	`atanl` (long double x)
	float	`atanf` (float x)

#include <complex.h>

	complex	`atan` (complex x)
	double complex	`catan` (double complex x)
	float complex	`catanf` (float complex x)
	long double complex	`catanl` (long double complex x)

Description

The atan function computes the principal value of the arc tangent of x, returning a value in the range $[-\pi/2, +\pi/2]$ . The arc tangent is also often denoted as $\tan^{-1}(x)$ .

The complex inverse tangent is defined by:

(1)

$\mathrm{atan}(x) = \frac{-1}{2} i \log \left( \frac{1+i x}{1-i x} \right)$

Example 1:

#include <stdio.h>
#include <math.h>
 
int main(void)
{
  double result, x = 0.6325;
  result = atan(x);
  printf("The arc sin of %lf is %lf\n", x, result);
}

Output:

The arc sin of 0.632500 is 0.563974

Special Values

atan ( ±0 ) returns ±0.
atan ( ±∞ ) returns ± $\pi/2$ .

Standards

The atan function conforms to ISO/IEC 9899:1999(E).

Compatibility

	DOS	UNIX	Windows	ANSI C	C++ only
atanl	•		•
Real atan	•	•	•	•
Complex atan	•		•		•
Complex catan		•			•

Last Modified: 2009-11-01 08:40:44 Page Rendered: 2010-03-14 08:20:06

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