# Source code for mars.tensor.arithmetic.arctanh

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Copyright 1999-2020 Alibaba Group Holding Ltd.
#
# you may not use this file except in compliance with the License.
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# Unless required by applicable law or agreed to in writing, software
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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import numpy as np

from ... import opcodes as OperandDef
from ..utils import infer_dtype
from .core import TensorUnaryOp
from .utils import arithmetic_operand

@arithmetic_operand(sparse_mode='unary')
class TensorArctanh(TensorUnaryOp):
_op_type_ = OperandDef.ARCTANH
_func_name = 'arctanh'

[docs]@infer_dtype(np.arctanh)
def arctanh(x, out=None, where=None, **kwargs):
"""
Inverse hyperbolic tangent element-wise.

Parameters
----------
x : array_like
Input tensor.
out : Tensor, None, or tuple of Tensor and None, optional
A location into which the result is stored. If provided, it must have
a shape that the inputs broadcast to. If not provided or None,
a freshly-allocated tensor is returned. A tuple (possible only as a
keyword argument) must have length equal to the number of outputs.
where : array_like, optional
Values of True indicate to calculate the ufunc at that position, values
of False indicate to leave the value in the output alone.
**kwargs

Returns
-------
out : Tensor
Array of the same shape as x.

Notes
-----
arctanh is a multivalued function: for each x there are infinitely
many numbers z such that tanh(z) = x. The convention is to return
the z whose imaginary part lies in [-pi/2, pi/2].

For real-valued input data types, arctanh 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, arctanh is a complex analytical function
that has branch cuts [-1, -inf] and [1, inf] and is continuous from
above on the former and from below on the latter.

The inverse hyperbolic tangent is also known as atanh or tanh^-1.

References
----------
..  M. Abramowitz and I.A. Stegun, "Handbook of Mathematical Functions",
10th printing, 1964, pp. 86. http://www.math.sfu.ca/~cbm/aands/
..  Wikipedia, "Inverse hyperbolic function",
http://en.wikipedia.org/wiki/Arctanh

Examples
--------
>>> import mars.tensor as mt

>>> mt.arctanh([0, -0.5]).execute()
array([ 0.        , -0.54930614])
"""
op = TensorArctanh(**kwargs)
return op(x, out=out, where=where)