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PARTVELVEC

PARTVELVEC

Name


      PARTVELVEC

Purpose


      Plot the velocity vectors of particles at their positions

Explanation


      This procedure plots the velocity vectors of particles (at the
      positions of the particles).
      For a similar procedure look at cgDrawVectors
        http://www.idlcoyote.com/idldoc/cg/cgdrawvectors.html

Category


      Plotting, Two-dimensional.

Calling Sequence


      PARTVELVEC, VELX, VELY, POSX, POSY [, X, Y]

Inputs


      VELX: An array of any dimension, containing the x-components
              of the particle velocities. Can include NaN values
      VELY: An array of the same dimension as velx, containing the
              y-components of the particle velocities.
      POSX: An array of the same dimension as velx, containing the
              x-components of the particle positions.
      POSY: An array of the same dimension as velx, containing the
              y-components of the particle positions.

Optional Inputs


      X: Optional abscissa values. X must be a vector.
      Y: Optional ordinate values. Y must be a vector. If only X
            is specified, then Y is taken equal to be equal to X.

Optional Input Keyword Parameters


      FRACTION: The fraction of the vectors to plot. They are
                  taken at random from the complete sample. Default is
              FRACTION = 1.0, use all vectors
      LENGTH: The maximum vectorlength relative to the plot data
                  window. Default = 0.08
      COLOR: Color for the vectors, axes and titles by string name or
                  number (see cgCOLOR). Note that if VECCOLORS is
                  supplied, then the COLOR keyword still specifies the
                  color of the axes and title. Default = 'Opposite'
      OVER: Plot over the previous plot
      VECCOLORS: The vector colors. Must be either a scalar, or
                  a vector (nmeric or string) the same size as VELX.
                  Set to COLOR by default.
      WINDOW - Set this keyword to plot to a resizeable graphics window
      Plot All other keywords available to cgPlot (e.g. AXISCOLOR,
      Keywords: LINESTYLE, XRANGE) are available (via _EXTRA)

Outputs


      This procedure plots the velocity vectors (VELX,VELY) at the
      positions of the particles, (POSX,POSY). If X and Y are not
      specified, then the size of the plot is such that all vectors
      just fit within in the plot data window.

Side Effects


      Plotting on the current device is performed.

Example


      Generate some particle positions and velocities.
        POSX=RANDOMU(seed,200)
        POSY=RANDOMU(seed,200)
        VELX=RANDOMU(seed,200)-0.5
        VELY=RANDOMU(seed,200)-0.5
      Plot the particle velocities.
        PARTVELVEC, VELX, VELY, POSX, POSY
      Example using vector colors.
        POSX=RANDOMU(seed,200)
        POSY=RANDOMU(seed,200)
        VELX=RANDOMU(seed,200)-0.5
        VELY=RANDOMU(seed,200)-0.5
        magnitude = SQRT(velx^2 + vely^2)
        LOADCT, 5, NCOLORS=254, BOTTOM=1 ; Load vector colors
        colors = BytScl(magnitude, Top=254) + 1B
        PARTVELVEC, VELX, VELY, POSX, POSY, COLOR='green', VECCOLORS=colors

Modification History


      Written by: Joop Schaye (jschaye@astro.rug.nl), Sep 1996.
      Added /OVER keyword Theo Brauers (th.brauers@fz-juelich.de) Jul 2002
      Added VECCOLORS keyword. David Fanning (david@dfanning.com) March, 2005
      Incorporate the Coyote Graphics (cg) plot programs WL January 2011
      Allow VELX, VELY to include NaN values P. Blitzer/WL March 2013
      Allow NOCLIP=0 when overplotting A. Negri October 2014



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