5.4.1 Quickstart: How to Make a Proper Parameter File

You will never write a new parameter file from scratch. Typically, you take an old file (e.g. the one controlling the simulation which produced the model which is used to start the new run) and edit it:

1. Take the parameter file corresponding to the model you want the new simulation to start with.

2. Most of the parameters should be already OK. E.g. most of the parameters controlling the boundaries do not have to be changed.

3. Write a brief description of the purpose of the planned simulation into the character description array. You might but a remark about the parent file of the parameter file under construction and the current date into the character history array (see Sect. 5.4.2).

4. Check/modify the name of start model and output files: infile_start, outfile_end, outfile_full, outfile_mean. On a system with batch queue this has not to be done in the parameter file itself but in the external command file (see Sect. 5.4.16).

5. Check/modify the fundamental parameters including boundary condition specifiers (see Sections 5.4.3 and 5.4.4, respectively)
   • effective temperature control (s_inflow, teff, luminositypervolume, C_radHtautop)
   • gravity (grav_mode, grav, mass_star, ...)
   • abundances (eosfile, opafile, check the paths!)

6. If the gravity of the new model (and therefore the characteristic time scale) significantly deviates from the old one, the time specifications controlling the output frequency (dtime_out_full, dtime_out_mean), the total length of the simulation (if specified as stellar time: endtime, plustime), and absolute boundaries/specifications for the time step (dtime_min, dtime_min_stop, dtime_max, dtime_start) have to be scaled. Look for parameters with units u=s (see Sections 5.4.15 and 5.4.16).

7. The rest of the parameters controls additional details. Most of the constants are specified in dimensionless form and keep their value in a class of related simulations. The previously used values will probably be reasonable for the new simulation, too.

Of course, a complete control of CO5BOLD is only possible after studying of the meaning of the parameters in detail (e.g. by reading the following pages) AND - unfortunately - an accompanying look into the source code itself.