% @(#)fft_fpow.hlq	17.1.1.1 (ESO-IPG) 01/25/02 17:43:35 
%++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
%.COPYRIGHT  (c)  1990 European Southern Observatory
%.IDENT      fft_fpow.hlq
%.AUTHOR     KB, IPG/ESO
%.KEYWORDS   MIDAS, help files, FFT/FPOWER
%.PURPOSE    On-line help file for the command: FFT/FPOWER
%.VERSION    1.0  03-APR-1990 : Creation, KB
%.VERSION    1.1  26-OCT-1992 : Upgrade, KB
%----------------------------------------------------------------
\se
SECTION./FPOW
\es\co
FFT/FPOWER						26-OCT-1992  KB
\oc\su
FFT/FPOWER inr ini outr outi pow_spec
        make discrete Fourier transform and power spectrum
\us\pu
Purpose:      
           Compute the discrete Fourier transform of real or complex frame
           and also its power spectrum (square root).
           Also shift origin of frequency domain to center of image.
\up\sub
Subject:      
           Transformation, filter.
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Syntax:       
           FFT/FPOWER inr ini outr outi pow_spec
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           inr = frame containing the real part of input frame
\ap\pa
           ini = frame containing the imaginary part of input frame;
\\
                if input frame is real, omit parameter `ini' or set it to `?'
                if you enter values for any of the following parameters.
\ap\pa
           outr = frame for real part of result transform,
                defaulted to `fftr.bdf'
\ap\pa
           outi = frame for imaginary part of result transform,
                defaulted to `ffti.bdf'
\ap\pa
           pow_spec = frame for power spectrum, defaulted to `power.bdf'
\ap\sa
See also:
           FFT/FINVERSE, FFT/FREQUENCY, FFT/POWER, CREATE/FILTER
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Note:
           All internal calculations are done in double precision and
           only the final result frames are truncated to single precision.
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           If the number of pixels in an axis of the input frame is not a power
           of 2, the input frame is expanded to the next higher power of 2.
           The result frames will have the original no. of pixels but the
           result frames with expanded size are also kept with names
           `exp_fftr.bdf', `exp_ffti.bdf' and `exp_pow.bdf'. These frames
           should be used later when calculating the inverse Fourier transform
           via FFT/FINVERSE!
\on\exs
Examples:
\ex
           FFT/FPOWER rr ri
            Do FFT for image where real part is contained in frame `rr.bdf'
            and imaginary part in frame `ri.bdf'. The real and imaginary parts
            of the FFT are stored in `fftr.bdf' and `ffti.bdf'; the power
            spectrum will be in frame `power.bdf'.
\xe\ex
           FFT/FPOWER lola ? zr zi zp
            Do FFT for real frame `lola.bdf' (no imaginary part) and store
            results in `zr.bdf', `zi.bdf' and `zp.bdf'.
\xe\sxe