Usage: 3dLocalPV [options] inputdataset
* You may want to use 3dDetrend before running this program,
   or at least use the '-polort' option.
* This program is highly experimental.  And slowish.
* Computes the SVD of the time series from a neighborhood of each
   voxel.  An inricate way of 'smoothing' 3D+time datasets, sort of.
* This is like 3dLocalSVD, except that the '-vproj' option doesn't
   allow anything but 1 and 2 dimensional projection.  This is because
   3dLocalPV uses a special method to compute JUST the first 1 or 2
   principal vectors -- faster than 3dLocalSVD, but less general.

 -mask mset          = restrict operations to this mask
 -automask           = create a mask from time series dataset
 -prefix ppp         = save SVD vector result into this new dataset
                        [default = 'LocalPV']
 -prefix2 qqq        = save second principal vector into this new dataset
                        [default = don't save it]
 -evprefix ppp       = save singular value at each voxel into this dataset
                        [default = don't save]
 -input inputdataset = input time series dataset
 -nbhd nnn           = e.g., 'SPHERE(5)' 'TOHD(7)' etc.
 -despike            = remove time series spikes from input dataset
 -polort p           = detrending
 -vnorm              = normalize data vectors [strongly recommended]
 -vproj [2]          = project central data time series onto local SVD vector;
                        if followed by '2', then the central data time series
                        will be projected on the 2-dimensional subspace
                        spanned by the first 2 principal SVD vectors.
                        [default: just output principal singular vector]
                        [for 'smoothing' purposes, '-vnorm -vproj' is an idea]

* On my Mac Pro, about 30% faster than 3dLocalSVD computing the same thing.
* If you're curious, the 'special method' used for the eigensolution is
  a variant of matrix power iteration, called 'simultaneous iteration'.
* By contrast, 3dLocalSVD uses EISPACK functions for eigensolution-izing.

* This binary version of 3dLocalPV is compiled using OpenMP, a semi-
   automatic parallelizer software toolkit, which splits the work across
   multiple CPUs/cores on the same shared memory computer.
* OpenMP is NOT like MPI -- it does not work with CPUs connected only
   by a network (e.g., OpenMP doesn't work with 'cluster' setups).
* For implementation and compilation details, please see
* The number of CPU threads used will default to the maximum number on
   your system. You can control this value by setting environment variable
   OMP_NUM_THREADS to some smaller value (including 1).
* Un-setting OMP_NUM_THREADS resets OpenMP back to its default state of
   using all CPUs available.
   ++ However, on some systems, it seems to be necessary to set variable
      OMP_NUM_THREADS explicitly, or you only get one CPU.
   ++ On other systems with many CPUS, you probably want to limit the CPU
      count, since using more than (say) 16 threads is probably useless.
* You must set OMP_NUM_THREADS in the shell BEFORE running the program,
   since OpenMP queries this variable BEFORE the program actually starts.
   ++ You can't usefully set this variable in your ~/.afnirc file or on the
      command line with the '-D' option.
* How many threads are useful? That varies with the program, and how well
   it was coded. You'll have to experiment on your own systems!
* The number of CPUs on this particular computer system is ...... 2.
* The maximum number of CPUs that will be used is now set to .... 2.

++ Compile date = May  7 2021 {AFNI_21.1.06:linux_ubuntu_16_64}