Scilab Function
Last update : 12/01/2004

atanh - hyperbolic tangent inverse

### Calling Sequence

  `t=atanh(x)`

### Parameters

- `x`: real or complex vector/matrix
- `t`: real or complex vector/matrix

### Description

The components of vector `t` are the hyperbolic tangent inverse of the corresponding entries of vector `x`. Definition domain is `[-1,1]` for the real function (see Remark).

### Remark

In Scilab (as in some others numerical software) when you try to evaluate an elementary mathematical function outside its definition domain in the real case, then the complex extension is used (with a complex result). The more famous example being the sqrt function (try `sqrt(-1)` !). This approach have some drawbacks when you evaluate the function at a singular point which may led to different results when the point is considered as real or complex. For the `atanh` this occurs for `-1` and `1` because the at these points the imaginary part do not converge and so `atanh(1) = +Inf + i NaN` while `atanh(1) = +Inf` for the real case (as lim x->1- of atanh(x)). So when you evaluate this function on the vector `[1 2]` then like `2` is outside the definition domain, the complex extension is used for all the vector and you get `atanh(1) = +Inf + i NaN` while you get `atanh(1) = +Inf` with `[1 0.5]` for instance.

### Examples

    // example 1
    x=[0,%i,-%i]
    tanh(atanh(x))

    // example 2
    x = [-%inf -3 -2 -1 0 1 2 3 %inf]
    ieee(2)
    atanh(tanh(x))

    // example 3 (see Remark)
    ieee(2)
    atanh([1 2])
    atanh([1 0.5])

### See Also

`tanh`, `ieee`,