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# numpy.arccosh

`numpy.``arccosh`(x[, out]) = <ufunc 'arccosh'>

  Inverse hyperbolic cosine, element-wise.

  Parameters : | x : array_like Input array. out : ndarray, optional Array of the same shape as x, to store results in. See `doc.ufuncs` (Section “Output arguments”) for details.
  Returns : | arccosh : ndarray Array of the same shape as x.

  See also

  `cosh`, `arcsinh`, `sinh`, `arctanh`, `tanh`

  Notes

  `arccosh` is a multivalued function: for each x there are infinitely many numbers z such that cosh(z) = x. The convention is to return the z whose imaginary part lies in [-pi, pi] and the real part in `[0, inf]`.

  For real-valued input data types, `arccosh` always returns real output. For each value that cannot be expressed as a real number or infinity, it yields `nan` and sets the invalid floating point error flag.

  For complex-valued input, `arccosh` is a complex analytical function that has a branch cut [-inf, 1] and is continuous from above on it.

  References

  [R2] | M. Abramowitz and I.A. Stegun, “Handbook of Mathematical Functions”, 10th printing, 1964, pp. 86. http://www.math.sfu.ca/~cbm/aands/

  [R3] | Wikipedia, “Inverse hyperbolic function”, http://en.wikipedia.org/wiki/Arccosh

  Examples

      >>> np.arccosh([np.e, 10.0])
      array([ 1.65745445,  2.99322285])
      >>> np.arccosh(1)
      0.0