torch.fft.ihfft

torch.fft.ihfft(input, n=None, dim=- 1, norm=None, *, out=None) → Tensor

Computes the inverse of hfft().

input must be a real-valued signal, interpreted in the Fourier domain. The IFFT of a real signal is Hermitian-symmetric, X[i] = conj(X[-i]). ihfft() represents this in the one-sided form where only the positive frequencies below the Nyquist frequency are included. To compute the full output, use ifft().

Parameters

• input (Tensor) – the real input tensor

• n (int, optional) – Signal length. If given, the input will either be zero-padded or trimmed to this length before computing the Hermitian IFFT.

• dim (int, optional) – The dimension along which to take the one dimensional Hermitian IFFT.

• norm (str, optional) –

  Normalization mode. For the backward transform (ihfft()), these correspond to:

  • "forward" - no normalization

  • "backward" - normalize by 1/n

  • "ortho" - normalize by 1/sqrt(n) (making the IFFT orthonormal)

  Calling the forward transform (hfft()) with the same normalization mode will apply an overall normalization of 1/n between the two transforms. This is required to make ihfft() the exact inverse.

  Default is "backward" (normalize by 1/n).

Keyword Arguments

out (Tensor, optional) – the output tensor.

Example

>>> t = torch.arange(5)
>>> t
tensor([0, 1, 2, 3, 4])
>>> torch.fft.ihfft(t)
tensor([ 2.0000-0.0000j, -0.5000-0.6882j, -0.5000-0.1625j])

Compare against the full output from ifft():

>>> torch.fft.ifft(t)
tensor([ 2.0000-0.0000j, -0.5000-0.6882j, -0.5000-0.1625j, -0.5000+0.1625j,
        -0.5000+0.6882j])