CLI Documentation

Basic Usage

gsnap [options] snapshot_file_name
When no options are provided, GSnap computes the velocity dispersion along many randomly chosen directions. The measurements are centered on the center of mass of the stellar particles in the snapshot. The output quantities are:
1. The snapshot time.
2. The mean velocity dispersion over the set of random directions.
3. The median velocity dispersion.
4. The maximum velocity dispersion.
5. The minimum velocity dispersion.
6. The standard deviation of the velocity dispersions for the set of random directions.
7. The mass of the 1st black hole listed in the snapshot file.
8. The accretion rate, $\dot M$, of the first black hole.
9. The mass of the 2nd black hole listed in the snapshot file.
10. The accretion rate of the second black hole.
11. The separation distance between the first two black holes (this is only computed when black hole particles are specified using -t, or --types).
12. The relative speed of the first two black holes in the snapshot, measured in km/s (this is only computed when black hole particles are specified using -t, or --types).

Options

-i # this will likely be modified so that the required options --beg, etc are simply required arguments
Create interpolated snapshots. Requires --beg, --end, --out. See --frames.
-I # this will likely be modified so that the required options --beg, etc are simply required arguments
Create interpolated images. Requires --beg, --end, --out. See --frames.
-w WIDTH
Set the diffraction slit mask width to WIDTH.
-l LENGTH
Set the diffraction slit mask length to LENGTH.
-t ######
Specify the particle types to be viewed or analyzed. The string ###### is a six-character type specification string. Place a ’1′ in the specification string to specify that you want to include a particular particle type in the calculation. The types are:

0: gas / SPH particles
1: dark matter particles
2: disk particles
3: bulge particles
4: new star particles
5: black hole particles

-a AGE_CUT
Set the age-cutoff for computing velocity dispersion for stars based on their creation times / age. For AGE_CUT > 0, velocity dispersion will be measured using stars younger than AGE_CUT time units. For AGE_CUT < 0, the velocity dispersion will be measured using stars older than AGE_CUT time units.
-n # also see --which
Compute the stellar velocity dispersion of stars by centering the measurements on the black holes. The first black hole particle appearing in the snapshot is chosen as the focus point.
-c X Y Z
Center the image on the position (X, Y, Z).
--theta THETA --phi PHI

View the system along the ($\theta$ , $\phi$) direction in spherical coordinates.

--view method
Save an image of the snapshot to disk. The method is one of the following:

gas or g: Create a volume rendering of the gas component.
flux or f: Create a volume rendering of the light generated by stars. This creates smoothed distributions.
stars or s: Display the star paticles. This is the sae as the flux option except the starlight is not smoothed.
particles or p: Save a rendering of the raw particle positions projected onto an image plane. This is a very fast, low quality viewing method.
interactive or i: Open the interactive preview window. This allows you to rotate and zoom the snapshot interactively.

If gas is included using --types, the gas in the snapshot attenuates the starlight when using the flux or stars methods.

--which N
Specify which nucleus the velocity dispersion measurements will be centered upon. This implies -n.
--frames N
Specify the number of intermediate interpolated snapshots or images (this is used only with the -i and -I options).
--beg FIRST_FILE_NAME --end SECOND_FILE_NAME --out OUTPUT_FILE_NAME

Specify the name of the beginning (--beg) and ending (--end) input snapshot files as well as the base name for the interpolated snapshot output files (--out).

--dof D
Specify the depth of field (D) as a fraction of the depth of the viewing box.
--version
Print the version information.
--info
Display basic snapshot header information (snapshot time, number of particles, etc.).
--parfile PARAMETER_FILE_NAME
Specify the parameter (settings) file.
--params Keyword=value
--params "Keyword1=value1; Keyword2=value2 [;...]"
Allows you to set parameter file values on the command line. Any number of semicolon-delimited keyword-value pairs can be used.
--sigma
Compute sigma along only the direction specified by --theta, --phi with center specified by -c. Slit mask size can be specified in a parameter file or using the -w and -l flags.
--script SCRIPT_FILE_NAME
Run the GSnap script contained in the file, SCRIPT_FILE_NAME.
--prob
Output probability distribution histogram data of line-of-sight velocity dispersion along a set of random viewing directions. This histogram displays the probability of measuring velocity dispersion in several equally-spaced bins.