std::atanh(std::complex)

template< class T > 
complex<T> atanh( const complex<T>& z );

Computes the complex arc hyperbolic tangent of z with branch cuts outside the interval [−1; +1] along the real axis.

Parameters

Return value

If no errors occur, the complex arc hyperbolic tangent of z is returned, in the range of a half-strip mathematically unbounded along the real axis and in the interval [−iπ/2; +iπ/2] along the imaginary axis.

Error handling and special values

Errors are reported consistent with math_errhandling.

If the implementation supports IEEE floating-point arithmetic,

• std::atanh(std::conj(z)) == std::conj(std::atanh(z))
• std::atanh(-z) == -std::atanh(z)
• If z is (+0,+0), the result is (+0,+0)
• If z is (+0,NaN), the result is (+0,NaN)
• If z is (+1,+0), the result is (+∞,+0) and FE_DIVBYZERO is raised
• If z is (x,+∞) (for any finite positive x), the result is (+0,π/2)
• If z is (x,NaN) (for any finite nonzero x), the result is (NaN,NaN) and FE_INVALID may be raised
• If z is (+∞,y) (for any finite positive y), the result is (+0,π/2)
• If z is (+∞,+∞), the result is (+0,π/2)
• If z is (+∞,NaN), the result is (+0,NaN)
• If z is (NaN,y) (for any finite y), the result is (NaN,NaN) and FE_INVALID may be raised
• If z is (NaN,+∞), the result is (±0,π/2) (the sign of the real part is unspecified)
• If z is (NaN,NaN), the result is (NaN,NaN)

Notes

Although the C++ standard names this function "complex 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 "complex inverse hyperbolic tangent", and, less common, "complex area hyperbolic tangent".

Inverse hyperbolic tangent is a multivalued function and requires a branch cut on the complex plane. The branch cut is conventionally placed at the line segments (-∞,-1] and [+1,+∞) of the real axis. The mathematical definition of the principal value of the inverse hyperbolic tangent is atanh z =

Example

#include <complex>
#include <iostream>
 
int main()
{
    std::cout << std::fixed;
    std::complex<double> z1(2.0, 0.0);
    std::cout << "atanh" << z1 << " = " << std::atanh(z1) << '\n';
 
    std::complex<double> z2(2.0, -0.0);
    std::cout << "atanh" << z2 << " (the other side of the cut) = "
              << std::atanh(z2) << '\n';
 
    // for any z, atanh(z) = atanh(iz) / i
    std::complex<double> z3(1.0, 2.0);
    std::complex<double> i(0.0, 1.0);
    std::cout << "atanh" << z3 << " = " << std::atanh(z3) << '\n'
              << "atan" << z3 * i << " / i = " << std::atan(z3 * i) / i << '\n';
}

atanh(2.000000,0.000000) = (0.549306,1.570796)
atanh(2.000000,-0.000000) (the other side of the cut) = (0.549306,-1.570796)
atanh(1.000000,2.000000) = (0.173287,1.178097)
atan(-2.000000,1.000000) / i = (0.173287,1.178097)

See also