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FORCE_NEWTON

FORCE_NEWTON

Name


      FORCE_NEWTON

Purpose


      Calculates the gravitational force from a particle distribution
      at a list of positions.

Category


      Astro

Calling Sequence


      Result = FORCE_NEWTON(X, Y, Z, Xpart, Ypart, Zpart, Mass)

Inputs


      X: X coordinates at which to calculate forces.
      Y: Y coordinates at which to calculate forces.
      Z: Z coordinates at which to calculate forces.
      Xpart: X coordinates of particle positions defining the mass
              distribution.
      Ypart: Y coordinates of particle positions defining the mass
              distribution.
      Zpart: Z coordinates of particle positions defining the mass
              distribution.
      Mass: Mass of each particle.

Keyword Parameters


      LENGTHUNIT: Length unit, in cm (or kpc if /ASTRO is set). Default: 1kpc.
      MASSUNIT: Mass unit, in grams (or solar masses if /ASTRO is
                  set). Default: 1 solar mass.
      SOFTENING: Plummer softening length. Default: 0 (no softening).
      ASTRO: If /ASTRO is set then LENGTHUNIT and MASSUNIT are given
                  in kpc and solar masses respectively, otherwise they are
                  in CGS (Lengthunit in cm, Massunit in grams).

Outputs


      This function returns the gravitational force at each X,Y,Z position.
      If there are NPOS positions, Result is an NPOSx3 matrix.

Example


      Calculate the gravitational force on a line along the x-axis from
      6 point masses placed at the vertices of a cube:
      xmasspos = [-1,-1,-1,-1,1,1,1,1]
      ymasspos = [-1,-1,1,1,-1,-1,1,1]
      zmasspos = [-1,1,-1,1,-1,1,-1,1]
      masses = REPLICATE(1.,8)
      xlinepos = 0.1*FINDGEN(20)
      ylinepos = REPLICATE(0.,20)
      zlinepos = REPLICATE(0.,20)
      forces = FORCE_NEWTON(xlinepos, ylinepos, zlinepos, xmasspos, ymasspos,
        zmasspos, masses)

Modification History


      Written by: Jeremy Bailin
      10 June 2008 Public release in JBIU



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