From help-octave-request at bevo dot che dot wisc dot edu Wed Dec 25 22:04:09 2002
Subject: Re: octave and image processing
From: Paul Kienzle <pkienzle at users dot sourceforge dot net>
To: "Albert F. Niessner" <Al dot Niessner at jpl dot nasa dot gov>
Cc: Paul Kienzle <pkienzle at jazz dot ncnr dot nist dot gov>,    "John W. Eaton" <jwe@bevo.che.wisc.edu>,    help-octave mailing list <help-octave@bevo.che.wisc.edu>
Date: Wed, 25 Dec 2002 23:03:31 -0500

Albert F. Niessner wrote:
<snip>

>I do not think that the FFT can benefit from in-place operations either
>since in many instances you are going from a real matrix to a complex
>matrix. Hence, you always need to create a new array because of how real
>and complex are defined.
>
Real FFT returning complex results can be done in place.  In the case of 
FFTW the
returned array is R1 R2 ... Rn I1 I2 ... In which will need to be 
transposed to R1 I1 R2 I2 ... Rn In,
but that can be done in place as well.  There is the small problem that 
the octave types
associated with the data assume that the data still represents a real 
matrix rather than a complex
matrix.  Short of creating a new type specifically to handle transform 
pairs, I can't think of a way
to to handle this case, but for someone transforming signals close to 
the size of memory, adding a
new type may be worthwhile.

Paul Kienzle
pkienzle at users dot sf dot net



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