README for v4.0 of ddisk.pro, which is an IDL script that calculates dust abundances
over time for a debris-disk that is produced by a planetesimal disk that is grinding
away due to collisional erosion. For further details, see paper by J. Hahn (2010, ApJ)
titled 'Diagnosing Circumstellar Debris Disks', in file hahn_2010_apj.pdf

To execute, first edit the model's input parameters in file inputs.pro.
Then start IDL, and enter @ddisk at the prompt to execute the model.
Then enter @figs to run the script that will analyze the output and generate some figures.

The model's principal outputs are the 1D arrays a, e, beta, where a[i]=semimajor axis
of the dust in orbit i, e[i]=eccentricity, and beta[i]=dust size parameter. The 1d array
tau is the dimensionless time axis (called t* in the paper), such that the system time
in years is tau*T0_yr. The 2D array N contains the abundance of dust in the various
orbits at various times, such that N[i,j] is the number of dust grains in orbit a[i],e[i]
at time tau[j]. Of course, this code generates lots of other quantities as well,
so please read the comments in inputs.pro, ddisk.pro, and figs.pro to determine their
meaning.

Execution times depend sensitively on the input parameters. For instance, a run with
N_sizes=200, N_longitudes=100, and N_rings=1 executes in about 3 minutes on my desktop PC,
while a similar simulation with N_rings=5 requires 70 minutes.

If you don't have an IDL license, you should still be able to run this software. But I would
first have prepare my code so that it can be used with IDL's virtual machine, which is
a free download. Just let me know if there is any interest, and I will prepare the code.

Feel free to email me any suggestions or bug reports.

Joseph M. Hahn
Space Science Institute
jhahn@spacescience.org