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<div class="moz-cite-prefix">Le 10/10/2018 Ã 08:47, Samuel Gougeon a
écrit :<br>
</div>
<blockquote type="cite"
cite="mid:4f167b65-4986-7bd5-ccc7-68a4e99eed5b@free.fr">Le
09/10/2018 à 21:52, antoine monmayrant a écrit :
<br>
<blockquote type="cite">Hello Samuel,
<br>
<br>
Sorry I might not have made myself clear: fft and fftshift
provide the ability to perform transform along only one of the
dimensions of a multidimensional array.
<br>
Something like S(x,y,z) --[FFT along 3rd dim]-->
ffthift(ffft(S(x,y,z), -1,3),3)=Ŝ(x,y,kz).
<br>
In that case, you need to perform fft and eventually fftshift
along only the dimension of the transform.
<br>
ifftshift should also provide the same possibility to perform
the inverse transform: Ŝ(x,y,kz) --[IFFT along 3rd dim]-->
iffthift(ffft(Ŝ(x,y,kz), +1,3),3)=S(x,y,z).
<br>
<br>
This is a basic signal processing requirement in my field.
<br>
</blockquote>
<br>
Hello Antoine,
<br>
<br>
Yes, you are right: in case of directional FFT and odd number of
elements along the chosen direction, ifftshift can't presently be
used.
<br>
Could you please post the same remark on bugzilla? This bug/wish
is not yet reported.
<br>
</blockquote>
OK, I'll put it in my TODO-list.<br>
<blockquote type="cite"
cite="mid:4f167b65-4986-7bd5-ccc7-68a4e99eed5b@free.fr">
<br>
IMO we may propose and include it in Scilab as soon as for Scilab
6.0.2.
<br>
<br>
BTW, still IMO, fftshift and ifftshift should rather be merged in
a single function.
<br>
It's the same code, except a floor<=>ceil. This should
deserve just an option, not a separate dedicated function.
<br>
I guess that this separation likely comes from a kind of abusive
Matlab-like mimicry.
<br>
</blockquote>
Yes, I agree.<br>
But I don't see how we can merge the two without increasing the huge
halo of confusion that blurs the help pages and use of fft-related
functions¹ ².<br>
The first idea that came to my mind was to make one single fftshift
function where:<br>
 - if dim>0, you do direct shift (ie for a direct Fourier
transform) along dimension dim;<br>
 - if dim<0, you do inverse shift (ie for an inverse Fourier
transform) along dimension |dim|.<br>
But as "-1" means direct fft and "+1" inverse fft, mixing fft and
fftshift would be a real mess.<br>
<br>
Antoine<br>
¹ One I just discovered yesterday: the help page for fft is not
listed in "Scilab Help >> Signal Processing > Transforms "
! Only ifft is listed, cool, he? Of course, ifft points to "Scilab
Help >> Signal Processing > Transforms > fft". Idem for
dst, ...<br>
² Oh, and this one cool too: in the fft help page: <br>
"incr<br>
a vector of positive numbers with integer values, or a vector of
positive integers. <b>See the Description part for details.</b>"
but the Description never says what the heck "incr" is, does and
means.... Arghhh. It only appears once in an example of a "previous
syntax".<br>
<br>
<blockquote type="cite"
cite="mid:4f167b65-4986-7bd5-ccc7-68a4e99eed5b@free.fr">
<br>
Best regards
<br>
Samuel
<br>
<br>
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<br>
</blockquote>
<p><br>
</p>
<pre class="moz-signature" cols="72">--
+++++++++++++++++++++++++++++++++++++++++++++++++++++++
Antoine Monmayrant LAAS - CNRS
7 avenue du Colonel Roche
BP 54200
31031 TOULOUSE Cedex 4
FRANCE
Tel:+33 5 61 33 64 59
email : <a class="moz-txt-link-abbreviated" href="mailto:antoine.monmayrant@laas.fr">antoine.monmayrant@laas.fr</a>
permanent email : <a class="moz-txt-link-abbreviated" href="mailto:antoine.monmayrant@polytechnique.org">antoine.monmayrant@polytechnique.org</a>
+++++++++++++++++++++++++++++++++++++++++++++++++++++++
</pre>
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