[manual] fftw unclear to me

[David Bateman]

Francesco Potorti` wrote:
> In the manual, I read:
>
>      Manage FFTW wisdom data. Wisdom data can be used to significantly
>      accelerate the calculation of the FFTs but implies an initial cost
>      in its calculation. The wisdom used by Octave can be imported
>      directly, usually from a file /etc/fftw/wisdom, 
>
> What does this mean?  Precisely, what "directly" means?  What "usually"
> means?  Does Octave read /etc/fftw/wisdom at startup?  If not, how can
> one read it?
>   

When the FFTW library initializes it reads a system wide wisdom file 
independent of Octave. This allows FFTW wisdom to be shared between 
applications on the same platform. Also the location of the system wide 
wisdom file is system dependent, as it certainly isn't in 
/etc/fftw/wisdom for Windows.

>           WISDOM = fftw ('dwisdom')
>
>      will save the existing wisdom used by Octave to the string WISDOM.
>      This string can then be saved in the usual manner. 
>
> What is "the usual manner"?  If it means using 'save', that should be
> specified.
>   
save/load, fprintf/scanf, etc, etc, etc.

>      However, the wisdom data can be reloaded if it is saved to a file
>      as described above.  
>
> Same as above: if this means using 'load', that should be specified.
>   
Ok.

> 			  Also, any system-wide wisdom file that has
>      been found will also be used.
>
> Does this answer my question above?  I mean, does this mean that Octave
> reads /etc/fftw/wisdom at startup?
>   
Yes, though its repetitive and so it should be removed.. I propose the 
attached changeset. Does it address your concerns?

D.


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David Bateman                                David.Bateman at motorola.com
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