# Source code for mars.tensor.arithmetic.expm1

```#!/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 TensorExpm1(TensorUnaryOp):
_op_type_ = OperandDef.EXPM1
_func_name = "expm1"

[docs]@infer_dtype(np.expm1)
def expm1(x, out=None, where=None, **kwargs):
"""
Calculate ``exp(x) - 1`` for all elements in the tensor.

Parameters
----------
x : array_like
Input values.
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
Element-wise exponential minus one: ``out = exp(x) - 1``.

--------
log1p : ``log(1 + x)``, the inverse of expm1.

Notes
-----
This function provides greater precision than ``exp(x) - 1``
for small values of ``x``.

Examples
--------
The true value of ``exp(1e-10) - 1`` is ``1.00000000005e-10`` to
about 32 significant digits. This example shows the superiority of
expm1 in this case.

>>> import mars.tensor as mt

>>> mt.expm1(1e-10).execute()
1.00000000005e-10
>>> (mt.exp(1e-10) - 1).execute()
1.000000082740371e-10
"""
op = TensorExpm1(**kwargs)
return op(x, out=out, where=where)
```