**MOMENTS(1)** TIPSY COMMANDS **MOMENTS(1)**

## NAME

moments - write the shape as a funtion of radius

## SYNOPSIS

**moments** *box-number* *center-box-number* *particle* *binning* *bin-*
*number* *filename* *minimum***_***radius*

## DESCRIPTION

**moments** is a command that produces a file of name, *file-*
*name,* that contains various physical parameters that
relate to the shape and orientation of the density distri-
bution for particles of type *particle* in box, *box-number.*
If the boxes *box-number* or *center-box-number* are not
loaded an error is generated. The shapes and orientations
are calculated using the iterative technique described in
Katz (Ap.J. 368:325, 1991). The initial guess for the
center of the density distribution is taken to be the cen-
ter of mass of box *center-box-number.* The *binning* argu-
ment refers to how the particles are binned, either lin-
early or log in radius. There are *bin-number* equal size
bins distributed equally in radius or log radius between
*minimum***_***radius* and the size of box *box-number* depending on
the *binning* argument. The output file has the following
columns: radius, b/a, c/a, phi, theta, psi, center-x,cen-
ter-y,and center-z where b/a refers to the ratio between
the intermediate axis and the long axis and c/a refers to
the ratio between the short and long axes. Phi, theta and
psi refer to the Euler angles that describe the orienta-
tion of the density distribution.

## OPTIONS

**Particle**
The possible choices for *particle* are:
**all**
Use the all the particles in box *box-number*
**dark**
Use only the dark matter particles in box *box-*
*number*
**gas**
Use only the gas particles in box *box-number*
**star**
Use only the star particles in box *box-number*
**Binning**
The possible choices for *binning* are:
**lin**
Make *bin-number* bins spaced equally in radius
between *minimum-radius* and the size of box *box-*
*number*
**log**
Make *bin-number* bins spaced equally in log
radius between *minimum-radius* and the size of
box *box-number*

## SEE ALSO

**profile(1)**, **rotationcurve(1)**,

## BUGS

The technique doesn't always converge, particularily when
the density distribution is very clumpy. Things converge
much better when the box *center-box-number* contains the
true center for the density distribution in box *box-number*
and is as small as possible.
KQ Release 2.0 22 MARCH 1994 **MOMENTS(1)**

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