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Module « scipy.special »

Fonction powm1 - module scipy.special

Signature de la fonction powm1

def powm1(*args, **kwargs) 

Description

help(scipy.special.powm1)

powm1(x1, x2, /, out=None, *, where=True, casting='same_kind', order='K', dtype=None, subok=True[, signature])

powm1(x, y, out=None)

Computes ``x**y - 1``.

This function is useful when `y` is near 0, or when `x` is near 1.

The function is implemented for real types only (unlike ``numpy.power``,
which accepts complex inputs).

Parameters
----------
x : array_like
    The base. Must be a real type (i.e. integer or float, not complex).
y : array_like
    The exponent. Must be a real type (i.e. integer or float, not complex).

Returns
-------
array_like
    Result of the calculation

Notes
-----
.. versionadded:: 1.10.0

The underlying code is implemented for single precision and double
precision floats only.  Unlike `numpy.power`, integer inputs to
`powm1` are converted to floating point, and complex inputs are
not accepted.

Note the following edge cases:

* ``powm1(x, 0)`` returns 0 for any ``x``, including 0, ``inf``
  and ``nan``.
* ``powm1(1, y)`` returns 0 for any ``y``, including ``nan``
  and ``inf``.

This function wraps the ``powm1`` routine from the
Boost Math C++ library [1]_.

References
----------
.. [1] The Boost Developers. "Boost C++ Libraries". https://www.boost.org/.

Examples
--------
>>> import numpy as np
>>> from scipy.special import powm1

>>> x = np.array([1.2, 10.0, 0.9999999975])
>>> y = np.array([1e-9, 1e-11, 0.1875])
>>> powm1(x, y)
array([ 1.82321557e-10,  2.30258509e-11, -4.68749998e-10])

It can be verified that the relative errors in those results
are less than 2.5e-16.

Compare that to the result of ``x**y - 1``, where the
relative errors are all larger than 8e-8:

>>> x**y - 1
array([ 1.82321491e-10,  2.30258035e-11, -4.68750039e-10])

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