flopscope.

flopscope.numpy.fft.irfft2

fnp.fft.irfft2(a, s=None, axes=(-2, -1), norm=None, out=None)[flopscope source][numpy source]

Computes the inverse of `rfft2`.

Adapted from NumPy docs np.fft.irfft2

Areafft
Typecustom
NumPy Refnp.fft.irfft2
Cost
5(N/2)⋅⌈log⁡2N⌉5(N/2) \cdot \lceil\log_2 N\rceil
Flopscope Context

Inverse 2-D real FFT. Cost: 5*(N//2)*ceil(log2(N)), N=prod(s) (Cooley-Tukey radix-2; Van Loan 1992 §1.4).

Computes the inverse of rfft2.

Parameters

a:array_like

The input array

s:sequence of ints, optional

Shape of the real output to the inverse FFT.

Changed in version 2.0.
Deprecated since 2.0.
Deprecated since 2.0.
axes:sequence of ints, optional

The axes over which to compute the inverse fft. Default: (-2, -1), the last two axes.

Deprecated since 2.0.
norm:{"backward", "ortho", "forward"}, optional

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

Added in version 1.20.0.
out:ndarray, optional

If provided, the result will be placed in this array. It should be of the appropriate shape and dtype for the last transformation.

Added in version 2.0.0.

Returns

out:ndarray

The result of the inverse real 2-D FFT.

See also

  • rfft2 The forward two-dimensional FFT of real input, of which irfft2 is the inverse.
  • rfft The one-dimensional FFT for real input.
  • irfft The inverse of the one-dimensional FFT of real input.
  • irfftn Compute the inverse of the N-dimensional FFT of real input.

Notes

This is really irfftn with different defaults. For more details see irfftn.

Examples

>>> import flopscope.numpy as fnp
>>> a = flops.mgrid[:5, :5][0]
>>> A = flops.fft.rfft2(a)
>>> flops.fft.irfft2(A, s=a.shape)
array([[0., 0., 0., 0., 0.],
       [1., 1., 1., 1., 1.],
       [2., 2., 2., 2., 2.],
       [3., 3., 3., 3., 3.],
       [4., 4., 4., 4., 4.]])