numpy.fft.irfftn¶

numpy.fft.
irfftn
(a, s=None, axes=None, norm=None)[source]¶ Compute the inverse of the Ndimensional FFT of real input.
This function computes the inverse of the Ndimensional discrete Fourier Transform for real input over any number of axes in an Mdimensional array by means of the Fast Fourier Transform (FFT). In other words,
irfftn(rfftn(a), a.shape) == a
to within numerical accuracy. (Thea.shape
is necessary likelen(a)
is forirfft
, and for the same reason.)The input should be ordered in the same way as is returned by
rfftn
, i.e. as forirfft
for the final transformation axis, and as forifftn
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, wheres[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.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 : {None, “ortho”}, optional
New in version 1.10.0.
Normalization mode (see
numpy.fft
). Default is None.Returns: out : ndarray
The truncated or zeropadded 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*(m1)
wherem
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
Notes
See
fft
for definitions and conventions used.See
rfft
for definitions and conventions used for real input.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.]]])