SOCRATES.jl Julia wrapper for SOCRATES radiative transfer codes

This provides a Julia module wrapping the SOCRATES Fortran radiance_core code.

SOCRATES Types (control, radout, etc) can be examined and modified from the Julia REPL (fields appear as Julia properties, ie use . instead of %).

SOCRATES functions (radiance_core) can be called using the same syntax as Fortran.

Building the wrappers

1. Check out SOCRATES (revision um13.0 from 2022-07-28 used for these tests)

2. Modify SOCRATES make/Mk_cmd_xxx to add -fPIC flag (for gfortran) to build 'position independent code' for a shared library. and build SOCRATES as usual (we need the radlib.a library)

3. Regenerate Fortran and Julia wrappers: a) Check ./julia/src/generate_wrappers.jl SOCRATES_DIR - path to SOCRATES source tree on local machine SVN_REV - (integer) svn revision b) Create an empty ./julia/gen folder (to contain generated wrappers) c) Activate Julia environment in ./julia folder: julia> ] activate . (SOCRATES) instantiate d) Build wrappers julia> cd("src") julia> include("generate_wrappers.jl")

4. Build shared library in julia/lib, using 'make' from linux command prompt (tested on Ubuntu linux, Makefile will probably need modifying for mac etc) This builds a shared library that includes the SOCRATES radlib.a + extra C wrapper functions

   NB: RAD_BIN must be set eg by . ./set_rad_env (see note in Makefile)

Examples

SOCRATES clear sky minimal test case (LW flux, no absorption)

Minimal example to demonstrate Julia <--> Fortran integration

Example from https://code.metoffice.gov.uk/trac/socrates/wiki/SocratesDoc/ClearskyFluxExample (clear sky fluxes, based on examples/netcdf/CIRC_case6)

Produces expected result (eg flux_down = 0, flux_up = constant for lw, no absorber case)

To run the Julia example script:

• Edit julia/test/test_clearsky.jl to set path to SOCRATES source tree on local machine (for data and example files)

• From Julia, starting in the ./julia folder: julia> ] activate . julia> cd("test/") julia> include("test_clearsky.jl")

Implementation

The overall strategy is to map Fortran types into Julia handle or proxy types that contain an opaque C pointer holding the memory reference to the Fortran instance.

SOCRATES types are wrapped by autogenerating code for a Julia handle type (holding a pointer to the Fortran type), and get / set functions. Two files are generated for each Type: a Fortran file providing C-callable functions using ISO_C_BINDING, and a Julia file with a Julia type definition, and functions including getproperty, setproperty and propertynames.

SOCRATES module parameters (for integer and string constants) are translated into Julia modules with corresponding const variables.

Top-level SOCRATES functions (calc_radiance) etc are hand-written.