Execution times in C05.07

Section 15.19 of Hazy 1 version 05.07 describes several ways to speed up the calculation.  This document adds to that discussion.

There have been two major improvements in the infrastructure of the code since the release of C96.01.  One is the definition of a fine continuum and opacity grid that is used to automatically account for line overlap.  Figure 20 of Shaw et al. (2005; ApJ 624, 794; Astro-ph 0501485) shows an example of this fine mesh.  Multi-grid is used to propagate this fine mesh onto the coarse mesh that is used to evaluate photo rates.  Currently this is only important when the large H2 and Fe II models are used.  The fine grid can safely be turned off with the "no fine opacities" command.  This will result in a 10 - 20% speed up with little loss of physical fidelity when the large models are not used.

The chemistry network has been extensively revised and extended by Nick Abel (see Abel et al; 2005, ApJ in press, astro-ph/0506514).  The chemistry is evaluated whenever the gas kinetic temperature is below 20,000 K.  If you are confident that molecules are not important, for instance, if only the H+ region is simulated, then the chemistry network can be turned off with the "no molecules" command.  This results in a 10-20% speed up.  There is little loss of physical fidelity if molecules really are not important, but this is dangerous if the simulation extends into neutral regions.

Good luck,
Gary Ferland