Compilation & Configuration

rbsolve leverages conditional compilation to enable or disable major model components and optimizations without branching the code. This is managed via the src/config.h file.

Basic Build

To compile the model on macOS or Linux:

cd src/
make clean
make inicond
make

This produces two executables: 1. inicond: Generates the initial condition files. 2. rb: The main simulation binary.

config.h Options

The config.h file contains C-preprocessor macros that fundamentally alter the equations or I/O methods. Once you change these, you must recompile the code.

Key definitions:

  • #define TEMPERATURE: Includes the active temperature scalar field, necessary for Rayleigh-Bénard convection.

  • #define SALINITY: Enables a second active scaler (e.g., for double-diffusive convection).

  • #define NETCDF_OUTPUT: Overrides the legacy unformatted binary grid outputs, saving standard .nc NetCDF4 files in physical space.

  • #define SAVE_PRESSURE: Instructs the code to explicitly write the pressure field p to disk alongside velocity and temperature. Note that pressure can also be diagnostically recovered from the velocity field.

  • #define PRINF: Enables the calculation of the pressure influence matrix (usually for specialized boundary conditions).

  • #define LINSTABDBG: Outputs extensive diagnostic information on linear stability to unit 20.

Example Configuration

To run a classical Rayleigh-Bénard setup with standard NetCDF output:

// Inside config.h
#define TEMPERATURE
#undef SALINITY
#define NETCDF_OUTPUT
#undef SAVE_PRESSURE
#undef PRINF

After editing, run make clean and make to apply.

MPI Compilation

To compile the code for distributed memory execution across multiple cores using MPI:

  1. Edit the Makefile: Open src/Makefile (or src/Makefile.macos) and comment out the NOMPI macro at the top of the file:

    # Comment this line for MPI
# NOMPI = 1

  2. Edit the Grid Parameters: The MPI domain decomposition is hardcoded at compile time. Open src/param.h and locate the #ifndef NOMPI block at the bottom. Change the NPROC parameter to exactly match the number of cores you intend to run on (e.g., NPROC=2). Note that the vertical grid resolution Ny dictates the Nylmem slice thickness requirement.

  3. Recompile & Run: Clean the build directory and recompile. The Makefile will automatically switch to using mpif77/mpif90.

    make clean
make inicond
make

    You can then launch the binaries using your system’s MPI launcher:

    mpirun -np 2 ./inicond
mpirun -np 2 ./rb