Method: Numo::Pocketfft.fftconvolve

Defined in:

lib/numo/pocketfft.rb

.fftconvolve(a, b) ⇒ Numo::DFloat/Numo::DComplex

Convolve two N-dimensinal arrays using dscrete Fourier Transform.

Examples:

require 'numo/pocketfftw'

a = Numo::DFloat[1, 2, 3]
b = Numo::DFloat[4, 5]
p Numo::Pocketfft.fftconvolve(a, b)
# Numo::DFloat#shape=[4]
# [4, 13, 22, 15]

a = Numo::DFloat[[1, 2], [3, 4]]
b = Numo::DFloat[[5, 6], [7, 8]]
p Numo::Pocketfft.fftconvolve(a, b)
# Numo::DFloat#shape=[3,3]
# [[5, 16, 12],
#  [22, 60, 40],
#  [21, 52, 32]]

Parameters:

• a (Numo::DFloat/Numo::DComplex) —

  Fisrt input array with any-dimension.

• b (Numo::DFloat/Numo::DComplex) —

  Second input array with the same number of dimensions as first input array.

Returns:

• (Numo::DFloat/Numo::DComplex) —

  The discrete linear convolution of ‘a’ with ‘b’.

Raises:

• (ArgumentError) —

  This error is raised if input arrays are not Numo::NArray, are not the same dimensionality, or are empty.

# File 'lib/numo/pocketfft.rb', line 192

def fftconvolve(a, b)
  raise ArgumentError, 'Expect class of input array to be Numo::NArray.' unless a.is_a?(Numo::NArray) && b.is_a?(Numo::NArray)
  raise ArgumentError, 'Expect input array to be non-empty.' if a.empty? || b.empty?
  raise ArgumentError, 'Input arrays should have the same dimensionarity' if a.ndim != b.ndim

  ashp = a.shape
  bshp = b.shape

  return a * b if (ashp + bshp).all? { |el| el == 1 }

  retshp = Array.new(a.ndim) { |n| ashp[n] + bshp[n] - 1 }
  a_zp = Numo::DComplex.zeros(*retshp).tap { |arr| arr[*ashp.map { |n| 0...n }] = a }
  b_zp = Numo::DComplex.zeros(*retshp).tap { |arr| arr[*bshp.map { |n| 0...n }] = b }
  ret = ifftn(fftn(a_zp) * fftn(b_zp))

  return ret if a.is_a?(Numo::DComplex) || a.is_a?(Numo::SComplex) || b.is_a?(Numo::DComplex) || b.is_a?(Numo::SComplex)

  ret.real
end