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Module « scipy.fft »

Fonction ifft2 - module scipy.fft

Signature de la fonction ifft2

def ifft2(x, s=None, axes=(-2, -1), norm=None, overwrite_x=False, workers=None, *, plan=None) 

Description

help(scipy.fft.ifft2)

Compute the 2-D inverse discrete Fourier Transform.

This function computes the inverse of the 2-D discrete Fourier
Transform over any number of axes in an M-D array by means of
the Fast Fourier Transform (FFT). In other words, ``ifft2(fft2(x)) == x``
to within numerical accuracy. By default, the inverse transform is
computed over the last two axes of the input array.

The input, analogously to `ifft`, should be ordered in the same way as is
returned by `fft2`, i.e., it should have the term for zero frequency
in the low-order corner of the two axes, the positive frequency terms in
the first half of these axes, the term for the Nyquist frequency in the
middle of the axes and the negative frequency terms in the second half of
both axes, in order of decreasingly negative frequency.

Parameters
----------
x : array_like
    Input array, can be complex.
s : sequence of ints, optional
    Shape (length of each axis) of the output (``s[0]`` refers to axis 0,
    ``s[1]`` to axis 1, etc.). This corresponds to `n` for ``ifft(x, n)``.
    Along each axis, if the given shape is smaller than that of the input,
    the input is cropped. If it is larger, the input is padded with zeros.
    if `s` is not given, the shape of the input along the axes specified
    by `axes` is used.  See notes for issue on `ifft` zero padding.
axes : sequence of ints, optional
    Axes over which to compute the FFT. If not given, the last two
    axes are used.
norm : {"backward", "ortho", "forward"}, optional
    Normalization mode (see `fft`). Default is "backward".
overwrite_x : bool, optional
    If True, the contents of `x` can be destroyed; the default is False.
    See :func:`fft` for more details.
workers : int, optional
    Maximum number of workers to use for parallel computation. If negative,
    the value wraps around from ``os.cpu_count()``.
    See :func:`~scipy.fft.fft` for more details.
plan : object, optional
    This argument is reserved for passing in a precomputed plan provided
    by downstream FFT vendors. It is currently not used in SciPy.

    .. versionadded:: 1.5.0

Returns
-------
out : complex ndarray
    The truncated or zero-padded input, transformed along the axes
    indicated by `axes`, or the last two axes if `axes` is not given.

Raises
------
ValueError
    If `s` and `axes` have different length, or `axes` not given and
    ``len(s) != 2``.
IndexError
    If an element of `axes` is larger than the number of axes of `x`.

See Also
--------
fft2 : The forward 2-D FFT, of which `ifft2` is the inverse.
ifftn : The inverse of the N-D FFT.
fft : The 1-D FFT.
ifft : The 1-D inverse FFT.

Notes
-----
`ifft2` is just `ifftn` with a different default for `axes`.

See `ifftn` for details and a plotting example, and `fft` for
definition and conventions used.

Zero-padding, analogously with `ifft`, is performed by appending zeros to
the input along the specified dimension. Although this is the common
approach, it might lead to surprising results. If another form of zero
padding is desired, it must be performed before `ifft2` is called.

Examples
--------
>>> import scipy.fft
>>> import numpy as np
>>> x = 4 * np.eye(4)
>>> scipy.fft.ifft2(x)
array([[1.+0.j,  0.+0.j,  0.+0.j,  0.+0.j], # may vary
       [0.+0.j,  0.+0.j,  0.+0.j,  1.+0.j],
       [0.+0.j,  0.+0.j,  1.+0.j,  0.+0.j],
       [0.+0.j,  1.+0.j,  0.+0.j,  0.+0.j]])

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