initial_xa_calculator is a utility that takes as argument 
i) the name of the mesa network file (in mesa/data/net_data/nets/), 
ii) initial [Fe/H], 
iii) and intial [alpha/Fe], 
iv) as well as an optional dY/dZ. 

It creates as output an initial_xa file for use with MESA/star. The file can be used when either 

      set_uniform_initial_xa_from_file = .true.

or

      set_uniform_xa_from_file = .true.

in the star_job section of the MESA inlist. The initial_xa filename is, by default, input_initial_composition.data and so should be set in the same inlist as

      file_for_uniform_xa = 'input_initial_composition.data'

It is current with MESA modules as of the 9575 release (02/2017).

The program relies on several MESA modules. To compile the code requires that:

i) MESA is installed and
ii) the MESA_DIR environment variable is set. Otherwise you must set it explicitly in src/makefile.

To compile, simply execute the mk script, as 

./mk

Running the program without any commmand line arguments will generate the following output:

usage:
    ./initial_xa_calculator [net_name] [Fe/H] [alpha/Fe] {dY/dZ}
     net_name = mesa/net network 
     [Fe/H] = 0 for solar
     [alpha/Fe] = 0 for solar
     dY/dZ = 1.5 by default, OPTIONAL

initial_xa_calculator is basedon the Asplund et al. (2009) solar abundance scale.

For nets with more than one isotope of the same element, the isotope fractions are set using the Lodders 2003 table in mesa/chem.
Isotope fractions are always required to sum to 1.

The code follows the MESA convention (by default, see 'dump_missing_metals_into_heaviest' in star_job) to add the fraction of all elements missing from the net to the heaviest element in the net.