std::atanh

float       atanh( float arg );

double      atanh( double arg );

long double atanh( long double arg );

double      atanh( IntegralType arg );

Computes the inverse hyperbolic tangent of arg.

Parameters

Return value

If no errors occur, the inverse hyperbolic tangent of arg (tanh-1
(arg), or artanh(arg)), is returned.

If a domain error occurs, an implementation-defined value is returned (NaN where supported).

If a pole error occurs, ±HUGE_VAL, ±HUGE_VALF, or ±HUGE_VALL is returned (with the correct sign).

If a range error occurs due to underflow, the correct result (after rounding) is returned.

Error handling

Errors are reported as specified in math_errhandling.

If the argument is not on the interval [-1, +1], a range error occurs.

If the argument is ±1, a pole error occurs.

If the implementation supports IEEE floating-point arithmetic (IEC 60559),

• if the argument is ±0, it is returned unmodified
• if the argument is ±1, ±∞ is returned and FE_DIVBYZERO is raised.
• if |arg|>1, NaN is returned and FE_INVALID is raised.
• if the argument is NaN, NaN is returned

Notes

Although the C standard (to which C++ refers for this function) names this function "arc hyperbolic tangent", the inverse functions of the hyperbolic functions are the area functions. Their argument is the area of a hyperbolic sector, not an arc. The correct name is "inverse hyperbolic tangent" (used by POSIX) or "area hyperbolic tangent".

POSIX specifies that in case of underflow, arg is returned unmodified, and if that is not supported, an implementation-defined value no greater than DBL_MIN, FLT_MIN, and LDBL_MIN is returned.

Example

#include <iostream>
#include <cmath>
#include <cfloat>
#include <cerrno>
#include <cfenv>
#include <cstring>
#pragma STDC FENV_ACCESS ON
int main()
{
    std::cout << "atanh(0) = " << std::atanh(0) << '\n'
              << "atanh(-0) = " << std::atanh(-0.0) << '\n'
              << "atanh(0.9) = " << std::atanh(0.9) << '\n';
     // error handling 
     errno = 0; std::feclearexcept(FE_ALL_EXCEPT);
     std::cout << "atanh(-1) = " << std::atanh(-1) << '\n';
     if(errno == ERANGE)
         std::cout << "    errno == ERANGE: " << std::strerror(errno) << '\n';
     if(std::fetestexcept(FE_DIVBYZERO))
        std::cout << "    FE_DIVBYZERO raised\n";
}

atanh(0) = 0
atanh(-0) = -0
atanh(0.9) = 1.47222
atanh(-1) = -inf
    errno == ERANGE: Numerical result out of range
    FE_DIVBYZERO raised

See also

External links

Weisstein, Eric W. "Inverse Hyperbolic Tangent." From MathWorld--A Wolfram Web Resource.