Module « numpy.matlib »

Fonction exp - module numpy.matlib

Signature de la fonction exp

Description

exp.__doc__

exp(x, /, out=None, *, where=True, casting='same_kind', order='K', dtype=None, subok=True[, signature, extobj])

Calculate the exponential of all elements in the input array.

Parameters
----------
x : array_like
    Input values.
out : ndarray, None, or tuple of ndarray 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 array is returned. A tuple (possible only as a
    keyword argument) must have length equal to the number of outputs.
where : array_like, optional
    This condition is broadcast over the input. At locations where the
    condition is True, the `out` array will be set to the ufunc result.
    Elsewhere, the `out` array will retain its original value.
    Note that if an uninitialized `out` array is created via the default
    ``out=None``, locations within it where the condition is False will
    remain uninitialized.
**kwargs
    For other keyword-only arguments, see the
    :ref:`ufunc docs <ufuncs.kwargs>`.

Returns
-------
out : ndarray or scalar
    Output array, element-wise exponential of `x`.
    This is a scalar if `x` is a scalar.

See Also
--------
expm1 : Calculate ``exp(x) - 1`` for all elements in the array.
exp2  : Calculate ``2**x`` for all elements in the array.

Notes
-----
The irrational number ``e`` is also known as Euler's number.  It is
approximately 2.718281, and is the base of the natural logarithm,
``ln`` (this means that, if :math:`x = \ln y = \log_e y`,
then :math:`e^x = y`. For real input, ``exp(x)`` is always positive.

For complex arguments, ``x = a + ib``, we can write
:math:`e^x = e^a e^{ib}`.  The first term, :math:`e^a`, is already
known (it is the real argument, described above).  The second term,
:math:`e^{ib}`, is :math:`\cos b + i \sin b`, a function with
magnitude 1 and a periodic phase.

References
----------
.. [1] Wikipedia, "Exponential function",
       https://en.wikipedia.org/wiki/Exponential_function
.. [2] M. Abramovitz and I. A. Stegun, "Handbook of Mathematical Functions
       with Formulas, Graphs, and Mathematical Tables," Dover, 1964, p. 69,
       http://www.math.sfu.ca/~cbm/aands/page_69.htm

Examples
--------
Plot the magnitude and phase of ``exp(x)`` in the complex plane:

>>> import matplotlib.pyplot as plt

>>> x = np.linspace(-2*np.pi, 2*np.pi, 100)
>>> xx = x + 1j * x[:, np.newaxis] # a + ib over complex plane
>>> out = np.exp(xx)

>>> plt.subplot(121)
>>> plt.imshow(np.abs(out),
...            extent=[-2*np.pi, 2*np.pi, -2*np.pi, 2*np.pi], cmap='gray')
>>> plt.title('Magnitude of exp(x)')

>>> plt.subplot(122)
>>> plt.imshow(np.angle(out),
...            extent=[-2*np.pi, 2*np.pi, -2*np.pi, 2*np.pi], cmap='hsv')
>>> plt.title('Phase (angle) of exp(x)')
>>> plt.show()