Computes a complex fast Fourier transform (FFT) using double precision.

r_in—The real part of the complex array to be transformed.

i_in—The imaginary part of the complex array to be transformed.

r_out—The real part of the transformed array.

i_out—The imaginary part of the transformed array.

Backward—If present and nonzero, an inverse FFT is computed.

DCMPLXFFT uses the real FFT provided by FFTCOMP to compute a complex FFT in double precision.

In the PV‑WAVE Reference: FFT