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Computing › C › Math.h ›

atan

Arc tangent function of one variable

View other versions (4)

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:

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

(1)

Example:

Example - Arc tangent function of one variable

Workings

#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);
}

Solution

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		•			•

Page Comments

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

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