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Henrik-Knierim / mesa_custom_EoS

A module to implement your EoS into MESA!
GNU General Public License v3.0
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mesa_custom_EoS

mesa_custom_EoS is an extension to MESA to implement user-defined equations of state. It uses the run_star_extras functionality.

Implementing your own EoS

[!NOTE] Prerequisites: The EoS you want to implement must be formatted like the other MESA EoS tables.

Using the placeholder

mesa_custom_EoS comes with a placeholder for your EoS. This placeholder only works if you use equally spaced EoS tables from 0 to 1 in steps of 0.1 in X and Z. To use it, you need to do the following:

  1. Add your EoS tables to the src/data folder of your work directory.
  2. Either rename the EoS folder inside src/data to my_eosDT and the EoS tables to my_eosDT_<Z>z<X>x.data, where <Z> and <X> are the $Z$ and $X$ values of the EoS table in percentage (e.g., my_eosDT_50z20x.data), or change data_dir_name and data_file_name in custom_eos.f90 (line 356 and 357) to the name of your EoS folder and the name of your EoS tables, respectively.
  3. Run ./mk to compile the code and make sure that eos_integer_ctrl(1) is set to 1 in your inlist.

    Creating your own EoS entry

    To go one step furhter and implement your own EoS(s), with different X and Z scaling, you need to do the following:

  4. Add the folder that contains your EoS tables to the src/data folder of your work directory. Then inside custom_eos.f90:
  5. Define the two parameters num_<eos_name>_Zs and num_<eos_name>_Xs that contain the number of $X$ and $Z$ values in your EoS tables. For example, if your EoS tables range from $X = 0$ to $X = 1$ in steps of $0.1$ and from $Z = 0$ to $Z = 1$ in steps of $0.1$, you would define: 
    integer, parameter :: num_<eos_name>_Zs = 11
integer, parameter :: num_<eos_name>_Xs = 11
  6. Define the array <eos_name>_XZ_loaded of boolean parameters with dimension (eos_<eos_name>_Xs, eos_<eos_name>_Zs). This array will be used to check if the EoS tables have been loaded. For example: 
    logical, dimension(num_<eos_name>_Xs, num_<eos_name>_Zs) :: <eos_name>_XZ_loaded
  7. Define a DT_XZ_Info type target that contains the information about the $(X,Z)$ grid of your EoS tables. Sticking with the example above, you would define: 
    type (DT_XZ_Info), target :: <eos_name>_XZ_struct
  8. Define another target of type EosDT_XZ_Info of the dimensions (num_<eos_name>_Zs, num_<eos_name>_Xs). This object will store the EoS table data. Again, for the example above: 
    type (EosDT_XZ_Info), dimension(num_<eos_name>_Xs, num_<eos_name>_Zs), target :: qeos_<eos_name>_data
  9. Define an id for your EoS with the name eosdt_<eos_name>. This is the integer that you will use in the inlist to select your EoS. For example: 
    integer, parameter :: eosdt_<eos_name> = 4
  10. Inside the eos_init_custom_eos subroutine, add a pointer of type DT_XZ_Info called <eos_name>_ptr. It will be used to populate <eos_name>_XZ_struct. In addition, set <eos_name>_XZ_loaded to .false.. The DT_XZ_Info type has the following properties: nZs stores the number of $Z$ values in your EoS tables, Zs is a 1D array that contains these $Z$ values, nXs_for_Z is a 1D array that contains the number of $X$ values for each $Z$ value and Xs_for_Z is a 2D array that contains the $X$ values for each $Z$ value.

For the example from above, we can make use:


! pointer to the EoS XZ structure
type (DT_XZ_Info), pointer :: <eos_name>_XZ_ptr

! #Z values in the EoS XZ structure
real(dp) :: <eos_name>_spacing(1:11) = &
    (/ 0.00d0, 0.1d0, 0.2d0, 0.3d0, 0.4d0, 0.5d0, 0.6d0, &
    0.7d0, 0.8d0, 0.9d0, 1.0d0 /)

! tracking if a table was already loaded
<eos_name>_XZ_loaded(:,:)=.false.

! < ... code populating the other "struct" variables ... >

!> <eos_name>
<eos_name>_XZ_ptr => <eos_name>_XZ_struct
<eos_name>_ptr % nZs = <number of z values>
<eos_name>_ptr % Zs(1: <eos_name>_ptr % nZs) = <Z values>
<eos_name>_ptr % nXs_for_Z(1: <eos_name>_ptr % nZs) = <eos_name>_ptr % nXs_for_Z(1: <eos_name>_ptr % nZs)
<eos_name>_XZ_ptr % Xs_for_Z(1: <eos_name>_XZ_ptr % nXs_for_Z(1), 1: <eos_name>_XZ_ptr % nZs) = &
<eos_name>_ptr % Xs_for_Z(1: <eos_name>_ptr % nXs_for_Z(1), 1: <eos_name>_ptr % nZs)
  1. Now, go through the rest of the code and anywhere the code checks for which_eosdt, add an else if statement for your EoS. For example: 
    if (which_eosdt == eosdt_my_eos) then
ep => my_eos_XZ_struct
else if (which_eosdt == eosdt_<eos_name>) then
xz => <eos_name>_XZ_struct
else
write(*,*) 'unknown which_eosdt supplied'
ierr = -1
return
end if
  2. Lastely, run ./mk to compile the code and change the eos_integer_ctrl(1) to the integer you defined in step 6, i.e. eosdt_<eos_name>.