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c99 [ flag... ] file... -lm [ library... ] #include <math.h> double atanh(double x);
float atanhf(float x);
long double atanhl(long double x);
These functions compute the inverse hyperbolic tangent of their argument x.
Upon successful completion, these functions return the inverse hyperbolic tangent of their argument.
If x is \(+-1, a pole error occurs and atanh(), atanhf(), and atanhl() return the value of the macro HUGE_VAL, HUGE_VALF, and HUGE_VALL, respectively, with the same sign as the correct value of the function.
For finite |x| > 1, a domain error occurs and a NaN is returned.
If x is NaN, NaN is returned.
If x is +0, x is returned.
If x is +Inf, a domain error occurs and a NaN is returned.
For exceptional cases, matherr(3M) tabulates the values to be returned by atanh() as specified by SVID3 and XPG3.
These functions will fail if:
Domain Error
The x argument is finite and not in the range [-1,1], or is \(+-Inf. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, the invalid floating-point exception is raised. The atanh() function sets errno to EDOM if the absolute value of x is greater than 1.0.
Pole Error
The x argument is \(+-1. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the divide-by-zero floating-point exception is raised. The atanh() function sets errno to ERANGE if the absolute value of x is equal to 1.0.
An application wanting to check for exceptions should call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an exception has been raised. An application should either examine the return value or check the floating point exception flags to detect exceptions.
An application can also set errno to 0 before calling atanh(). On return, if errno is non-zero, an error has occurred. The atanhf() and atanhl() functions do not set errno.
See attributes(5) for descriptions of the following attributes:
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
| Interface Stability | Standard |
| MT-Level | MT-Safe |
feclearexcept(3M), fetestexcept(3M), math.h(3HEAD), matherr(3M), tanh(3M), attributes(5), standards(5)