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snapcmp - compare two N-body snapshots


snapcmp in1=snap_file in2=snap_file [parameter=value] ...


snapcmp is a flexible tool for comparing two N-body snapshots on a particle by particle basis. An arbitrary ‘‘observable’’ defined in terms of the basic components of a body(3NEMO) may be specified for the comparison. Particles are compared by differencing their observables, or by computing the observable applied to a differenced particle. These options cover most of the common methods of comparing N-body snapshots. The default settings compute the magnitude of the configuration-space displacements between each pair of particles.

The program simply outputs eight numbers: time of the first snapshot, are the minimum, lower quartile, median, upper quartile, maximum of the measured differences, and the mean and dispersion of the distribution.


The following parameters are recognized.
Input data is read from snap_file1 and snap_file2, which must be in snapshot(5NEMO) format. Default: none.
Data with time values within time_range1 and time_range2 will be read from snap_file1 and snap_file2, respectively. [Default: all].
obs_expression is the observable used to compare the particles. See bodytrans(1NEMO) for the form of obs_expression. Default: r, which compares the positions of particles.
If flag is true, particles are compared by subtracting the components of one from the components of the other, and evaluating the observable obs on this ‘‘differenced particle’’. Otherwise, obs is evaluated for each particle, and the results are differenced. Default: true.
If flag is true, the differenced observable is divided by the value of obs computed from the particle in snap_file1. Otherwise, the differenced observable is used. Default: false.
Show (10-base) logarithms of the values instead of their linear values Default: false.

See Also

snapcmphist(1NEMO) , snapdiff(1NEMO) , bodytrans(3NEMO) , snapshot(5NEMO)


src/nbody/reduc/snapcmp.c      source code for snapcmp, snapcmphist and


Joshua E. Barnes.


23-may-88    V1.0 created?    Josh
29-mar-94    V1.3 added time to output    Peter
15-apr-04    V1.5 added headline= to the plotting versions and  mean,sigma  to
the output    PJT
16-jul-09    V1.6 added log=    PJT

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