Module « numpy.fft »

Fonction irfftn - module numpy.fft

Signature de la fonction irfftn

def irfftn(a, s=None, axes=None, norm=None) 

Description

irfftn.__doc__

    Computes the inverse of `rfftn`.

    This function computes the inverse of the N-dimensional discrete
    Fourier Transform for real input over any number of axes in an
    M-dimensional array by means of the Fast Fourier Transform (FFT).  In
    other words, ``irfftn(rfftn(a), a.shape) == a`` to within numerical
    accuracy. (The ``a.shape`` is necessary like ``len(a)`` is for `irfft`,
    and for the same reason.)

    The input should be ordered in the same way as is returned by `rfftn`,
    i.e. as for `irfft` for the final transformation axis, and as for `ifftn`
    along all the other axes.

    Parameters
    ----------
    a : array_like
        Input array.
    s : sequence of ints, optional
        Shape (length of each transformed axis) of the output
        (``s[0]`` refers to axis 0, ``s[1]`` to axis 1, etc.). `s` is also the
        number of input points used along this axis, except for the last axis,
        where ``s[-1]//2+1`` points of the input are used.
        Along any axis, if the shape indicated by `s` 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. Except for the last axis which is taken to
        be ``2*(m-1)`` where ``m`` is the length of the input along that axis.
    axes : sequence of ints, optional
        Axes over which to compute the inverse FFT. If not given, the last
        `len(s)` axes are used, or all axes if `s` is also not specified.
        Repeated indices in `axes` means that the inverse transform over that
        axis is performed multiple times.
    norm : {"backward", "ortho", "forward"}, optional
        .. versionadded:: 1.10.0

        Normalization mode (see `numpy.fft`). Default is "backward".
        Indicates which direction of the forward/backward pair of transforms
        is scaled and with what normalization factor.

        .. versionadded:: 1.20.0

            The "backward", "forward" values were added.

    Returns
    -------
    out : ndarray
        The truncated or zero-padded input, transformed along the axes
        indicated by `axes`, or by a combination of `s` or `a`,
        as explained in the parameters section above.
        The length of each transformed axis is as given by the corresponding
        element of `s`, or the length of the input in every axis except for the
        last one if `s` is not given.  In the final transformed axis the length
        of the output when `s` is not given is ``2*(m-1)`` where ``m`` is the
        length of the final transformed axis of the input.  To get an odd
        number of output points in the final axis, `s` must be specified.

    Raises
    ------
    ValueError
        If `s` and `axes` have different length.
    IndexError
        If an element of `axes` is larger than than the number of axes of `a`.

    See Also
    --------
    rfftn : The forward n-dimensional FFT of real input,
            of which `ifftn` is the inverse.
    fft : The one-dimensional FFT, with definitions and conventions used.
    irfft : The inverse of the one-dimensional FFT of real input.
    irfft2 : The inverse of the two-dimensional FFT of real input.

    Notes
    -----
    See `fft` for definitions and conventions used.

    See `rfft` for definitions and conventions used for real input.

    The correct interpretation of the hermitian input depends on the shape of
    the original data, as given by `s`. This is because each input shape could
    correspond to either an odd or even length signal. By default, `irfftn`
    assumes an even output length which puts the last entry at the Nyquist
    frequency; aliasing with its symmetric counterpart. When performing the
    final complex to real transform, the last value is thus treated as purely
    real. To avoid losing information, the correct shape of the real input
    **must** be given.

    Examples
    --------
    >>> a = np.zeros((3, 2, 2))
    >>> a[0, 0, 0] = 3 * 2 * 2
    >>> np.fft.irfftn(a)
    array([[[1.,  1.],
            [1.,  1.]],
           [[1.,  1.],
            [1.,  1.]],
           [[1.,  1.],
            [1.,  1.]]])