A New Formulation of the Fast Fractional Fourier Transform

  • Authors:
  • Rafael G. Campos;J. Rico-Melgoza;Edgar Chávez

  • Affiliations:
  • rcampos@umich.mx and elchavez@umich.mx;jerico@umich.mx;-

  • Venue:
  • SIAM Journal on Scientific Computing
  • Year:
  • 2012

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Abstract

By using a spectral approach, we derive a Gaussian-like quadrature of the continuous fractional Fourier transform. The quadrature is obtained from a bilinear form of eigenvectors of the matrix associated to the recurrence equation of the Hermite polynomials. These eigenvectors are discrete approximations of the Hermite functions, which are eigenfunctions of the fractional Fourier transform operator. This new discrete transform is unitary and has a group structure. By using some asymptotic formulas, we rewrite the quadrature in terms of the fast Fourier transform (FFT), yielding a fast discretization of the fractional Fourier transform and its inverse in closed form. We extend the range of the fractional Fourier transform by considering arbitrary complex values inside the unit circle and not only at the boundary. We find that this fast quadrature evaluated at $z=i$ becomes a more accurate version of the FFT and can be used for nonperiodic functions.