INVERSE FFT Information Technology （逆FFT 信息技术）.pdf

INVERSE FFT Mathematics LET Subcommands INVERSE FFT PURPOSE Compute the discrete inverse fast Fourier transform of a variable. DESCRIPTION The Fourier transform converts a time domain function into a frequency domain function while the inverse Fourier transform converts a frequency domain function into a time domain function. If h(t) represents the function in the time domain and H(f) represents the function in the frequency domain, then the definitions of the Fourier transform and the inverse Fourier transformation respectively are: ∞ H f 2π ift (EQ 3-46) ( ) = ∫ h (t )e dt –∞ ∞ h (t ) = ∫ H (f )e–2π ift df (EQ 3-47) –∞ In practice, functions are sampled at equally spaced discrete points. The discrete Fourier transform and the discrete inverse Fourier transforms respectively are: N – 1 2π ikn