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<p><tt>Dear Miguel,</tt></p>
<p><tt> the FFT types have been simplified. As described in
fft_fwinv.f90</tt></p>
<p><tt></tt><br>
!! **grid_type = 'Rho'** : <br>
!! fourier transform of potentials and charge density f<br>
!! <br>
!! **grid_type = 'Wave'** :<br>
!! ifourier transform of wave functions f<br>
!!<br>
!! **grid_type = 'tgWave'** :<br>
!! fourier transform of wave functions f with task group<br>
!!<br>
!! **dfft = FFT descriptor**, IMPORTANT NOTICE: grid is
specified only by dfft.<br>
</p>
<p>previously there was an unnecessary mixing between grid_type
(actually meaning fft_type ... we should rename it as such) and
FFT grid descriptors</p>
<p>Previously <br>
</p>
<p> 'Dense' could only be used with dfftp and transformed
density-like arrays <br>
</p>
<div class="moz-cite-prefix">'Smooth' could only be used with dffts
and transformed density-like arrays<br>
<br>
'Custom' could only use the custom grid and acted on density-like
arrays<br>
<br>
'Wave' could only be used with dffts and transformed wfc-like
arrays<br>
<br>
'tgWave' could only be used with dfft to transform wfc with
task-groups<br>
<br>
'CustomWave' could only use the custum grid to transform wfc-like
array<br>
<br>
consistency of fft_type and grid_descriptor was not internally
checked !<br>
<br>
Now <br>
<br>
Rho/Wave/tgWave tells which type of fft you are performing and the
fft descriptor tells which grid you are using. <br>
<br>
If the grid has not been initialized for that fft type an error
message is issued.<br>
<br>
in short<br>
<br>
'Dense' on dfftp became 'Rho' on dfftp<br>
'Smooth' on dffts became 'Rho' on dffts<br>
'Custom' on dfftt became 'Rho' on dfftt<br>
'Wave' on dffts became 'Wave' on dffts<br>
'CustomWave' on dfftt became 'Wave' on dfftt<br>
'tgWave' on dffts became 'tgWave' on dffts<br>
<br>
other combinations are possible if properly initialized but are
not currently used in QE<br>
<br>
best,<br>
<br>
stefano<br>
<br>
<br>
On 07/02/2018 16:28, Miguel Carvajal wrote:<br>
</div>
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<div>
<div>I seems that in the current codebase some renaming have
been made to the fft grids.<br>
</div>
Now there exist the `Rho` grid and the `Wave` grid. Can some
one explain the mappings from this new name to the old ones
and what happened to the `CustomWave` grid.<br>
</div>
Best regards,<br>
</div>
<br>
</div>
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style="padding:0px 15px 0px 5px"><b
style="color:rgb(51,51,51)">Miguel
Carvajal</b> PhD</span></div>
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<div class="gmail_quote">On Thu, Nov 9, 2017 at 6:51 AM, Carlo
Cavazzoni <span dir="ltr"><<a
href="mailto:c.cavazzoni@cineca.it" target="_blank"
moz-do-not-send="true">c.cavazzoni@cineca.it</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">It may
help thinking that we use fft to compute a non linear<br>
Operator (convolution), then the result is represented on<br>
A denser grid in order not to loose accuracy.<br>
So we end up with 2 fft grids, for each type,<br>
Whereas different types are needed to cope with different
observables<br>
With different basis sets.<br>
In principle we can do everything using just one grid, the
largest,<br>
But we would waste a lot of space and cycles<br>
<br>
Carlo<br>
<div>
<div class="h5">----- Stefano de Gironcoli <<a
href="mailto:degironc@sissa.it" moz-do-not-send="true">degironc@sissa.it</a>>
wrote:<br>
> It's confusing...<br>
><br>
> for a given grid there are two type of FFTs<br>
><br>
> the one used to transform wavefunctions, limited to
G-vectors up to Ecutwfc<br>
><br>
> and the one associated to the density/potential, up
to 4*Ecutwfc or Ecutrho<br>
><br>
> There are three grids. the Smooth one (dffts:
accommodating G-vectors up<br>
> to 4*Ecutwfc), the Dense one (dfftp: accommodating
G-vectors up to<br>
> Ecutrho) and the Custom one (used in exx
calculations), for a total of<br>
> 2x3 = 6 combinations.<br>
><br>
> only five are actually used:<br>
><br>
> Wave: transforms wavefunction on the smooth grid
(dffts)<br>
><br>
> Smooth: transforms densities/potentials on the
smooth grid (dffts)<br>
><br>
> Dense: transforms densities/potentials on the dense
grid (dfftp)<br>
><br>
> CustomWave: transforms wavefunction on the custom
grid<br>
><br>
> Custom: transforms densities/potentials on the
custom grid.<br>
><br>
> The missing combination (wavefunction on the dense
grid) is never needed.<br>
><br>
> It would make sense to redefine the type of fft as
'Rho/Wave' but for<br>
> historical and timing-definition reasons this is
not done (yet?).<br>
><br>
> Have a look to FFTXlib/fft_fwinv.f90 if you want to
see how things work<br>
> in detail.<br>
><br>
> ... and actually there are three types of FFTs:
Rho, Wave, and Wave with<br>
> task groups, the last one only used on the smooth
grid as<br>
> invfft/fwfft('tgWave', psic, dffts)<br>
><br>
> stefano<br>
><br>
><br>
> On 06/11/2017 14:01, Miguel Carvajal wrote:<br>
> > Dear all,<br>
> > can some one explain to me what is the
difference of calling<br>
> ><br>
> ><br>
> ><br>
> > CALL fwfft ('Custom', rhoc(:,ii), dfftt)<br>
> > CALL fwfft (‘Wave', rhoc(:,ii), dfftt)<br>
> > CALL fwfft (‘Dense', rhoc(:,ii),dfftt)<br>
> > CALL fwfft (’Smooth', rhoc(:,ii), dfftt)<br>
> > when doing FFT on QE; as well as the
appropriate grid to be used in<br>
</div>
</div>
> > each instance: *dfft, dfftp or dffts*.<br>
<span class="">> > I have some ideas but not a full
understanding of it.<br>
> > Best regards,<br>
> ><br>
> > Lic. Miguel Carvajal - Instituto Balseiro -
Bariloche<br>
> > National Atomic Energy Comission<br>
> > <a href="tel:%5B%2B54%5D%202944782429"
value="+542944782429" moz-do-not-send="true">[+54]
2944782429</a> (tel) / krvajal.miguel (skype)<br>
</span>> > LinkedIn: in/krvajal <<a
href="https://www.linkedin.com/in/krvajal/"
rel="noreferrer" target="_blank" moz-do-not-send="true">https://www.linkedin.com/in/<wbr>krvajal/</a>><br>
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