![[attach.png]](../idldoc-resources/attach.png)
astro/
shape_iterative.pro
top source shape_iterative
Astro
result = shape_iterative(pos, radius, masses=masses, r2weight=r2weight, shell=shell, axes=axes, fval=fval, maxit=maxit, verbose=verbose)
Given a 3-dimensional distribution of points, determines the best ellipsoidal shape using particles in an interatively-defined ellipsoid (or ellipsoidal shell) of the same shape.
Return value
The function returns a 3-element array containing the lengths of the principal axes of the ellipse.
Parameters
- pos in
An Nx3 array specifying the 3d positions of the N particles that make up the mass distribution.
- radius in
Radius at which to compute the shape. For a filled ellipsoid, this is the geometric mean radius of the principal axes that define the outer limits of the ellipsoid; for an ellipsoidal shell, this is the geometric mean radius at the center of the shell.
Keywords
- masses in
An N-element vector of the mass of each point. If not specified, all masses are assumed to be unity.
- r2weight in
If /R2WEIGHT is specified then particles are downweighted by a factor of 1/r^2 so that all particles have equal effect regardless of radius.
- shell in
Use an ellipsoidal shell rather than a filled ellipsoid. The value is the width of the shell.
- axes in
An output 3x3 array containing the principal axes. AXES[*,i] is the direction of the i-th principal axis.
- fval in
Iterate until the axis ratios and directions of the axes vary by less than FVAL. Default is 0.001.
- maxit in
Maximum number of iterations to allow. Default is 20.
- verbose in
Print information about each iteration.
Examples
Set up a 1/r^2 ellipsoidal density distribution and find its shape.
np = 100000
r = 200 * randomu(seed, np)
ph = 2. * !pi * randomu(seed, np)
th = acos(randomu(seed, np))
x = 2. * r * cos(ph) * sin(th)
y = r * sin(ph) * sin(th)
z = 3. * r * cos(th)
print, shape_iterative([[x],[y],[z]], 100., axes=axes)
print, axes
Author information
- History:
Written by: Jeremy Bailin 22 July 2011 Initial release
File attributes
| Modification date: | Fri Jul 22 15:00:20 2011 |
| Lines: | 126 |