Re: Complex -> Real FFT

[Jeff Wasserman <wasserman(at)ll.mit.edu>]

David Fanning wrote:
> 
> Jeremy Kepner (jvkepner@muse.Princeton.EDU) writes:
> 
> >   Does anyone know of a Complex to Real FFT that has
> > been implemented in IDL.  (Likewise a corresponding
> > Real to Complex FFT would also be nice).
> 
> I'm probably missing something deep here, but
> doesn't this do what you want?
> 
>    result = FLoat(complex_fft_expression)
>    result = Imaginary(complex_fft_expression)

If you don't care about phase information with your FFT data, and
instead want just an absolute power measurement (like a spectrum
analyzer), you could use
	power_spectrum = Abs(complex_fft_data)
[the abs function returns the value of sqrt(real^2+imaginary^2) if it's
argument is complex]
Conversely, you could also get the phase info into an array
	phase_array = Tan(complex_fft_data)
[The tan function also nicely works with complex data]
>From these two arrays you could then go back to the complex array. 
However, as far as I know, there is no way to obtain the two independent
variables of the original complex array after it's been converted to
reals.


------------------------------------------------------------
      Jeffrey Wasserman  -  Member of Technical Staff
      Group 83  Electro-Optical Materials and Devices
           MIT Lincoln Laboratory  Lexington, MA
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