External mesh input

SPIDER can accept a pre-computed mesh from an external file instead of computing one internally from the Adams-Williamson equation of state. This enables coupling with structure solvers like Zalmoxis that provide more accurate density profiles for non-Earth-like compositions.

1. Enable external mesh mode

Set these options when running SPIDER:

Option	Type	Description
`-MESH_SOURCE`	`int`	`0` (default): internal AW mesh. `1`: read from external file.
`-mesh_external_filename`	`string`	Path to external mesh file (required when `MESH_SOURCE=1`).

2. Prepare the mesh file

The mesh file is plain text (SI units), ordered from surface to CMB.

# <num_basic_nodes> <num_staggered_nodes>
r_b[0] P_b[0] rho_b[0] g_b[0]      (surface)
r_b[1] P_b[1] rho_b[1] g_b[1]
...
r_b[nb-1] P_b[nb-1] rho_b[nb-1] g_b[nb-1]  (CMB)
r_s[0] P_s[0] rho_s[0] g_s[0]      (staggered)
...
r_s[ns-1] P_s[ns-1] rho_s[ns-1] g_s[ns-1]

Rules

Columns are: radius [m], pressure [Pa], density [kg/m\(^3\)], gravity [m/s\(^2\)]
Ordering is surface (largest radius) to CMB (smallest radius)
Gravity should be negative (inward)
ns = nb - 1
First line starts with # and contains nb and ns

3. Quick example

# From SPIDER root
python tests/generate_aw_mesh.py -n 50 -o mesh.dat
./spider -options_file tests/opts/blackbody50.opts -MESH_SOURCE 1 -mesh_external_filename mesh.dat

EOS out-of-range

With EOS lookup tables such as WolfBower2018, SPIDER issues a one-time warning per table and direction when pressure or entropy lies outside the tabulated range; subsequent out-of-range queries are silently clamped.

If the thermal expansion coefficient alpha becomes negative near table boundaries, it is reset to zero with a warning to prevent NaNs in the mixing length theory.