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snaprect - diagonalize moment-of-inertia of snapshot
in=snap_file out=snap_file [parameter=value] ...
the input N-body snapshot to a coordinate system which diagonalizes the
moment-of-inertia tensor of a specified subset of particles (see keywords
weight, rcut and shell below). The centroid of the subset is translated
to the origin. As with snapkinem(1NEMO)
, an arbitrary weighting may be specified
for each particle.
Iterative determinations of the axis ratio, using the
moments of inertia, have been implemented on an experimental basis.
following parameters are recognized.
During iterations, the
printed output contains momentary eigenvectors and angles, not the cumulative
- Input data is read from
snap_file, which must be in snapshot(5NEMO)
format. Default: required.
- Output data is written to snap_file, in snapshot(5NEMO)
- Expression used to compute the weight of each
body. See bodytrans(1NEMO)
for the form of body_weight. Default: 1.0.
- If cutoff_radius is greater than zero, only particles within cutoff_radius
of the body_weighted centroid will be used to compute the moment-of-inertia.
- Only frames within time_range will be analyzed.
- Two radii are expected here. They define
an ellipsoidal shell within which the (modified) inertia tensor is computed
and iterated. Default: all particles.
- Maximum number of iterations
allowed in computing the inertia tensor within a changing volume/shell.
- Minimum tolerance required to stop iterations. [Default:
- Use modified inertia tensor? If set to true, the modified
(normalized w.r.t. the squared ellipsoidal radius from a previous iteraton)
inertia tensor is used instead of the regular one. Note that the body_weight
is also applied. It only makes sense to use this option if max_iters > 1.
- If a filename is given, it is expected to be
a snapshot. The first snapshot in this file is used to rectify all selected
snapshots from the inputfile. Default: none.
Aguilar & Meritt (1990) - ApJ 354, 33. Using a fraction of the most bound
Katz (1991) ApJ 368, 325. Volume iterative tensor.
Dubinski & Carlberg
(1991) ApJ 378, 496. Volume iterative modified tensor.
Kuijken & Dubinksi
(1994) MN 269, 13. Shell iterative modified tensor.
Joshua E. Barnes,
5-mar-89 original version? JEB
4-jul-94 finally implemented test=, also output theta/phi of p.axes PJT
24-jul-94 V1.4 experimental iters=, shell= PJT
15-mar-02 V1.4d addded log= keyword WD