Fast Fourier transform (FFT)

The routines for fast Fourier transform (and their origin) are:

• PDA_RFFTI, PDA_DRFFTI (FFTPACK/NETLIB)
  Initialize PDA_(D)RFFTF and PDA_(D)RFFTB.
• PDA_RFFTF, PDA_DRFFTF (FFTPACK/NETLIB)
  Forward transform of a real periodic sequence.
• PDA_RFFTB, PDA_DRFFTB (FFTPACK/NETLIB)
  Backward transform of a real coefficient array.
• PDA_CFFTI, PDA_DCFFTI (FFTPACK/NETLIB)
  Initialize PDA_(D)CFFTF and PDA_(D)CFFTB.
• PDA_CFFTF, PDA_DCFFTF (FFTPACK/NETLIB)
  Forward transform of a complex periodic sequence.
• PDA_CFFTB, PDA_DCFFTB (FFTPACK/NETLIB)
  Unnormalised inverse of PDA_(D)CFFTF.

• PDA_R2NAG, PDA_DR2NAG
  Convert real FFTPACK FT to NAG format.
• PDA_NAG2R, PDA_DNAG2R
  Convert real NAG FT to FFTPACK format.
• PDA_C2NAG, PDA_DC2NAG
  Convert complex FFTPACK FT to NAG format.
• PDA_NAG2C, PDA_DNAG2C
  Convert complex NAG FT to FFTPACK format.

• PDA_NFFTF, PDA_DNFFTF
  Forward transform of a complex, N-dimensional data array.
• PDA_NFFTB, PDA_DNFFTB
  Backward transform of a complex, N-dimensional coefficient array.