SMOOTH(2.0)                  SMOOTH                   SMOOTH(2.0)



NAME
     smooth - Calculate smoothed quantities over all particles

SYNOPSIS
     smooth [-s <nSmooth>[dgs]] [-b <nBucket>] [-g]
          [-o <Output Name>] [-p <xyzPeriod>]
          [-px <xPeriod>] [-py <yPeriod>] [-pz <zPeriod>]
          [density] [meanvel] [speed] [veldisp] [phase] [mach]
          [all] [null]
     Reads particles from stdin in the TIPSY BINARY format.


OPTIONS
     [-s <nSmooth>[dgs]]: Default nSmooth = 64 (dgs)
     Specifies the number of neighbors to smooth  over.  Directly
     following  the  integer any of the letters dgs may follow. A
     'd' specifies that smooth consider the dark  matter  in  the
     input file in its calculations. A 'g' sepecifies that smooth
     consider the gas in the input file and an 's' specifies that
     stars  are  to  be  considered. For example -s 64dgs (-s 64)
     would smooth over 64 particles considering all the matter in
     the  simulation (the default). Specifying -s 32gs would con-
     sider only the gas and the stars and ignore any dark  matter
     in the input file.

     [-b <nBucket>]: Default nBucket = 16
     Specifies the number of  particles  in  the  leaves  of  the
     search  tree.  This number can be changed to improve perfor-
     mance, but does not influence the calculation.

     [-g]: specifies that only the 'gather'  kernel  be  used  in
     calculating  mean quantities. The default is to use the full
     SPH gather-scatter kernel.

     [-o <Output Name>]: Default output name is "smooth".
     This argument allows the user to specify an alternate output
     name  to  be used for all the smooth outputs. For example -o
     dark would produce dark.den, dark.mvl, dark.dsp, etc.

     [-p <xyzPeriod>]: Default non-periodic in x, y and z  dimen-
     sions
     Specifies that smoothing take into  account  periodicity  in
     the   all   three   dimensions  given  by  the  same  period
     <xyzPeriod>. This is a shorthand  to  specifying  all  three
     parameters given below.

     [-px <xPeriod>]: Default non-periodic in x dimension
     Specifies that smoothing take into  account  periodicity  in
     the x-dimension given by the period <xPeriod>.

     [-py <yPeriod>] [-pz <zPeriod>]: As above.

     [density]: produces a density output  file  (smooth.den)  in
     tipsy ascii array format

     [meanvel]: produces a mean velocity output file (smooth.mvl)
     in tipsy ascii vector format

     [speed]: produces a mean speed output file  (smooth.spd)  in
     tipsy array format

     [veldisp]:  produces  a  velocity  dispersion  output   file
     (smooth.dsp) in tipsy array format

     [mach]: produces a mach number output file  (smooth.mch)  in
     tipsy array format

     [phase]: produces a phase density output  file  (smooth.phs)
     in tipsy array format

     [all]: produces all of the above output files

     [null]: produces no output files but  searches  for  nearest
     neighbors  and then gathers the nearest neighbors (Smoothing
     and Resmoothing). This is useful for gauging the performance
     of smooth.


DESCRIPTION
     Smooth can calculate several mean quantities for all  parti-
     cles  in  an N-Body simulation output file. The program pro-
     duces a file for each type of output specified on  the  com-
     mand  line.  This  output  file  is in ascii format with one
     smoothed quantity for each particle. The program uses a sym-
     metric  SPH (Smoothed Particle Hydrodynamics) smoothing ker-
     nel to find the mean quantities.

          <Ai> = SUMj(Aj*Mj/Dj*W(i,j)) over all j

     where <Ai> is the smoothed value for particle i of  quantity
     A, Mj is the Mass of particle j, Dj is the density of parti-
     cle j and W(i,j) is the symmetric smoothing  kernel  defined
     by,

          W(i,j) = 1/2(w(Rij,Hi) + w(Rij,Hj)) and,

     Rij is the distance from particle i to particle j.
     Hi is HALF the distance to the k'th most distant neighbor of
     particle i.

          w(R,H) = 1/(PI*H^3)*(1 - 0.75*(2 - R/H)*(R/H)^2
               if (R/H) < 1 and,

          w(R,H) = 1/(PI*H^3)*0.25*(2 - R/H)^3
               if (R/H) >= 1.

     The density for particle i is simply,

          Di = SUMj(Mj*W(i,j))

     Quantities which smooth will  calculate  are  density,  mean
     velocity,  mean  speed, velocity dispersion, mach number and
     phase density. For simulations which have periodic  boundary
     conditions,  the  periods  in  x, y, and z must be specified
     using the -px, -py and -pz arguments for smooth  to  produce
     the  correct  results  at the boundaries. As a shorthand, if
     the periods in the three dimensions are the same (usual) the
     -p argument suffices.


EXAMPLES
     > smooth density < tipsy.bin

     This produces a density output file called  smooth.den  from
     the  tipsy  binary  file tipsy.bin. The program has smoothed
     density over 64 (default) nearest neighbors and over all the
     particles in the tipsy.bin file.

     >  smooth  -s  32g  -o  tipsy_gas  density  veldisp  mach  <
     tipsy.bin

     This produces a density output file, tipsy_gas.den, a  velo-
     city dispersion output file, tipsy_gas.dsp and a mach number
     output file, tipsy_gas.mch.  Smoothing has been done over 32
     nearest  neighbors and taking into account only the gas par-
     ticles.

     > smooth -s 64d -px 256 -py 256 -pz 256 density <  tipsy.bin
     (or)

     > smooth -s 64d -p 256 density < tipsy.bin

     This produces a density output file, smooth.den,  which  has
     been  smoothed  over a periodic cube of 256 units to a side.
     Only the dark matter has been considered in calculating  the
     density.


NOTE ABOUT OUTPUT
     It is important  to  note  that  the  output  arrays  always
     correspond  to  the input file. For example if an input file
     is given with 32000 dark matter, 32000  gas  and  1000  star
     particles  the output tipsy array's will have 65000 entries,
     even if only the gas particles were smoothed over. The  par-
     ticles  which were ignored have a value of zero in the array
     or vector format.


WARNINGS
     When using periodic  boundary  conditions  assure  that  the
     periodicity  is  identical  to  that  used during the N-Body
     simulation which generated the input file being used.

     Smooth output files can be quite large  since  they  are  in
     ascii  format.   Make  sure  that  sufficient  disk space is
     available. When running smooth on several input  files  make
     sure  to specify unique output names for the files otherwise
     these files will simply be over-written.

     Smoothing time scales slightly worse than linear with number
     of  particles  and  linear  with  nSmooth (number of nearest
     neighbors).


BUGS
     Bugs? Not!


SEE ALSO
     tipsy(1), denmax(1), fof(1)

Stadel Release 2.0  Last change: 31 MAY 1994