### arctanh =====================================================================

Tags
----
scripting, JS, internal, treenode, general concept

Parameters
----------
x

General description
-------------------
Returns the inverse hyperbolic tangent of x.

###

Eval_arctanh = ->
  push(cadr(p1))
  Eval()
  arctanh()

arctanh = ->
  d = 0.0
  save()
  p1 = pop()
  if (car(p1) == symbol(TANH))
    push(cadr(p1))
    restore()
    return

  if (isdouble(p1))
    d = p1.d
    if (d < -1.0 || d > 1.0)
      stop("arctanh function argument is not in the interval [-1,1]")
    d = Math.log((1.0 + d) / (1.0 - d)) / 2.0
    push_double(d)
    restore()
    return

  if (isZeroAtomOrTensor(p1))
    push(zero)
    restore()
    return

  push_symbol(ARCTANH)
  push(p1)
  list(2)
  restore()