In real space processors are organized in a 2D pattern.

Each processor owns data from a sub-set of Z-planes and a sub-set of Y-planes.
In reciprocal space each processor owns Z-columns that belong to a sub set of
X-values. This allows to split the processors in two sets for communication
in the YZ and XY planes.
In alternative, if the situation allows for it, a task group paralelization is used
(with ntg=nyfft) where complete XY planes of ntg wavefunctions are collected and Fourier
trasnformed in G space by different task-groups. This is preferable to the Z-proc + Y-proc
paralleization if task group can be used because a smaller number of larger ammounts of 
data are transferred. Hence three types of fft are implemented: 
 
  !
  !! ... isgn = +-1 : parallel 3d fft for rho and for the potential
  !
  !! ... isgn = +-2 : parallel 3d fft for wavefunctions
  !
  !! ... isgn = +-3 : parallel 3d fft for wavefunctions with task group
  !
  !! ... isgn = +   : G-space to R-space, output = \sum_G f(G)exp(+iG*R)
  !! ...              fft along z using pencils        (cft_1z)
  !! ...              transpose across nodes           (fft_scatter_yz)
  !! ...              fft along y using pencils        (cft_1y)
  !! ...              transpose across nodes           (fft_scatter_xy)
  !! ...              fft along x using pencils        (cft_1x)
  !
  !! ... isgn = -   : R-space to G-space, output = \int_R f(R)exp(-iG*R)/Omega
  !! ...              fft along x using pencils        (cft_1x)
  !! ...              transpose across nodes           (fft_scatter_xy)
  !! ...              fft along y using pencils        (cft_1y)
  !! ...              transpose across nodes           (fft_scatter_yz)
  !! ...              fft along z using pencils        (cft_1z)
  !
  ! If task_group_fft_is_active the FFT acts on a number of wfcs equal to 
  ! dfft%nproc2, the number of Y-sections in which a plane is divided. 
  ! Data are reshuffled by the fft_scatter_tg routine so that each of the 
  ! dfft%nproc2 subgroups (made by dfft%nproc3 procs) deals with whole planes 
  ! of a single wavefunciton.
  !

fft_type module heavily modified, a number of variables renamed with more intuitive names 
(at least to me), a number of more variables introduced for the Y-proc parallelization.

Task_group module made void. task_group management is now reduced to the logical component
 fft_desc%have_task_groups of fft_type_descriptor type variable fft_desc.

In term of interfaces, the 'easy' calling sequences are

SUBROUTINE invfft/fwfft( grid_type, f, dfft, howmany )

  !! where:
  !! 
  !! **grid_type = 'Dense'** : 
  !!   inverse/direct fourier transform of potentials and charge density f
  !!   on the dense grid (dfftp). On output, f is overwritten
  !! 
  !! **grid_type = 'Smooth'** :
  !!   inverse/direct fourier transform of  potentials and charge density f
  !!   on the smooth grid (dffts). On output, f is overwritten
  !! 
  !! **grid_type = 'Wave'** :
  !!   inverse/direct fourier transform of  wave functions f
  !!   on the smooth grid (dffts). On output, f is overwritten
  !!
  !! **grid_type = 'tgWave'** :
  !!   inverse/direct fourier transform of  wave functions f with task group
  !!   on the smooth grid (dffts). On output, f is overwritten
  !!
  !! **grid_type = 'Custom'** : 
  !!   inverse/direct fourier transform of potentials and charge density f
  !!   on a custom grid (dfft_exx). On output, f is overwritten
  !! 
  !! **grid_type = 'CustomWave'** :
  !!   inverse/direct fourier transform of  wave functions f
  !!   on a custom grid (dfft_exx). On output, f is overwritten
  !! 
  !! **dfft = FFT descriptor**, IMPORTANT NOTICE: grid is specified only by dfft.
  !!   No check is performed on the correspondence between dfft and grid_type.
  !!   grid_type is now used only to distinguish cases 'Wave' / 'CustomWave' 
  !!   from all other cases
                                                                                                 

Many more files modified.




git-svn-id: http://qeforge.qe-forge.org/svn/q-e/trunk/espresso@13676 c92efa57-630b-4861-b058-cf58834340f0