# atanh, atanhf, atanhl

Calculates the inverse hyperbolic tangent.

## Syntax

``````double atanh( double x );
float atanhf( float x );
long double atanhl( long double x );
``````
``````float atanh( float x );  // C++ only
long double atanh( long double x );  // C++ only
``````

### Parameters

x
Floating-point value.

## Return Value

The atanh functions return the inverse hyberbolic tangent (arc hyperbolic tangent) of x. If x is greater than 1, or less than -1, errno is set to EDOM and the result is a quiet NaN. If x is equal to 1 or -1, a positive or negative infinity is returned, respectively, and errno is set to ERANGE.

Input SEH Exception Matherr Exception
± QNAN,IND none none
X ≥ 1; x ≤ -1 none none

## Remarks

Because C++ allows overloading, you can call overloads of atanh that take and return float or long double values. In a C program, atanh always takes and returns double.

## Requirements

atanh, atanhf, atanhl <math.h> <cmath> or <math.h>

For additional compatibility information, see Compatibility.

## Example

``````// crt_atanh.c
// This program displays the hyperbolic tangent of pi / 4
// and the arc hyperbolic tangent of the result.
//

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

int main( void )
{
double pi = 3.1415926535;
double x, y;

x = tanh( pi / 4 );
y = atanh( x );
printf( "tanh( %f ) = %f\n", pi/4, x );
printf( "atanh( %f ) = %f\n", x, y );
}
``````
``````tanh( 0.785398 ) = 0.655794
atanh( 0.655794 ) = 0.785398
``````