# Source code for mars.tensor.arithmetic.arccos

```#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Copyright 1999-2021 Alibaba Group Holding Ltd.
#
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#
# Unless required by applicable law or agreed to in writing, software
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and

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 TensorArccos(TensorUnaryOp):
_op_type_ = OperandDef.ARCCOS

_func_name = "arccos"

[docs]@infer_dtype(np.arccos)
def arccos(x, out=None, where=None, **kwargs):
"""
Trigonometric inverse cosine, element-wise.

The inverse of `cos` so that, if ``y = cos(x)``, then ``x = arccos(y)``.

Parameters
----------
x : array_like
`x`-coordinate on the unit circle.
For real arguments, the domain is [-1, 1].
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
-------
angle : Tensor
The angle of the ray intersecting the unit circle at the given
`x`-coordinate in radians [0, pi]. If `x` is a scalar then a
scalar is returned, otherwise an array of the same shape as `x`
is returned.

--------
cos, arctan, arcsin

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

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

The inverse `cos` is also known as `acos` or cos^-1.

References
----------
M. Abramowitz and I.A. Stegun, "Handbook of Mathematical Functions",
10th printing, 1964, pp. 79. http://www.math.sfu.ca/~cbm/aands/

Examples
--------
We expect the arccos of 1 to be 0, and of -1 to be pi:
>>> import mars.tensor as mt

>>> mt.arccos([1, -1]).execute()
array([ 0.        ,  3.14159265])

Plot arccos:

>>> import matplotlib.pyplot as plt
>>> x = mt.linspace(-1, 1, num=100)
>>> plt.plot(x.execute(), mt.arccos(x).execute())
>>> plt.axis('tight')
>>> plt.show()
"""
op = TensorArccos(**kwargs)
return op(x, out=out, where=where)
```