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snaphist - histogram of projected radii and radial velocities of a snapshot


snapscale in=in_file [parameter=value] ...


snaphist creates a histogram of projected radii and radial velocities of the particles in a snapshot. The histogram is weighted by the mass of the particles.

A number of random angles can optionally be choosen for each point to be rotated before it is projected. A random orientation is achieved by 2 rotations: one in polar angle phi (0..2PI) followed by a random value of cos(theta) where theta is 0..PI away from the Z axis. The histogram counts are then normalized by nrand. This then means that the histograms are completely normalized, it’s integral being the total mass.

A little on the background of this program: (dumbell)

snaphist does not use yapp(3NEMO) yet, it produces a table, meant for mongo(1LOCAL) or tabhist(1NEMO) .


The following parameters are recognized:
input file, in snapshot(5NEMO) format. [Default: none].
boundaries of the projected radii which should be used to construct the histogram. [0:2:0.05].
boundaries of the radial velocities which should be used to construct the histogram. [-2:2:0.1].
Number of random angles used for each point before it is projected. Only positive values are used. [default: 0].
A random seed for the random number generator. A value of zero means time of day is taken as random seed. [0].
Table needed of radii (r) or velocities (v). A scatter table of velocity vs. radius can be obtained with s. If the option rv is taken, and the number of bins in radius and velocity is the same, both radius and velocity columns will be output. Radius in columns 1 and 2, velocity in 3 and 4. [default: r].

See Also

snapprint(1NEMO) , tabhist(1NEMO) , tabplot(1NEMO)


When non-uniform bins are choosen, the centers of the bins appear in the table, which is not exactly understandable for mongo.


Peter Teuben


~/src/pjt/nbody       snaphist.c snaphist.1

Update History

19-jun-89    V1.0: created              PJT
27-jul-89    V1.1: more efficient random angles    PJT

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