#             exp(2 x) - 1
#  tanh(x) = --------------
#             exp(2 x) + 1



Eval_tanh = ->
  d = 0.0
  push(cadr(p1))
  Eval()
  p1 = pop()
  if (car(p1) == symbol(ARCTANH))
    push(cadr(p1))
    return
  if (isdouble(p1))
    d = Math.tanh(p1.d)
    if (Math.abs(d) < 1e-10)
      d = 0.0
    push_double(d)
    return
  if (isZeroAtomOrTensor(p1))
    push(zero)
    return
  push_symbol(TANH)
  push(p1)
  list(2)