Development

Architecture

src/
├── Lazy.jl              # Main module definition and version checking
├── cli.jl               # Command-line interface and user interaction
├── fitting.jl           # Core photometric redshift fitting algorithms
├── io.jl                # I/O operations, caching, and data management
├── utils.jl             # Utilities (progress bars, memory estimation, formatting)
├── template_grid.jl     # Template grid construction and IGM/CGM modeling
├── writedata.py         # Python interface for FITS I/O (via PyCall)
├── example_params.toml  # Example parameter file (used by `lazy params`)
├── templates/           # SED template library
│   └── template_directory.toml
├── filter_files/        # Filter transmission curves
│   └── filter_directory.toml
└── igm_data/            # IGM attenuation model data (Inoue+2014)

Data Flow

1. Input: FITS catalog + TOML parameter file

2. Template grid construction (template_grid.jl): Interpolate templates onto the redshift grid, apply IGM/CGM attenuation, integrate through filter bandpasses

3. Fitting (fitting.jl): For each object, solve non-negative least squares at every redshift to find the best-fit template combination

4. Output (io.jl): Write results to FITS or HDF5

Key Algorithms

• Non-negative least squares (NonNegLeastSquares.jl): Ensures template coefficients are non-negative (physically motivated – you can't have negative flux contributions)

• IGM attenuation: Inoue et al. (2014) model with Lyman-series and continuum absorption

• CGM damping wing: Asada et al. (2024) Lyman-alpha damping wing model

• P(z) computation: exp(-0.5 * chi2) normalized over the redshift grid

Contributing

Contributions are welcome, especially new filter transmission curves and template sets! If you've added filters for an instrument or survey not yet included, or have a useful template set, please submit a PR to make them available to the community.

1. Fork the repository

2. Create a feature branch: git checkout -b feature-name

3. Test your changes: julia --project=. -e "using Pkg; Pkg.test()"

4. Submit a pull request

Running Tests

julia --project=. -e "using Pkg; Pkg.test()"

The test suite covers CLI parsing, template/filter directory integrity, CGM model physics, and spectroscopic redshift fixing.

Extending Lazy.jl

Adding Templates

See Templates for the full guide. In brief: add files to src/templates/ and register them in template_directory.toml.

Adding Filters

See Filters for the full guide. In brief: add transmission curves to src/filter_files/ and register them in filter_directory.toml.

Other Extension Points

• IGM models: Add attenuation data to src/igm_data/ and implement the loader

• Template error functions: Add to src/templates/template_error/

• Output formats: Extend I/O functions in src/io.jl

• Fitting algorithms: Modify the core fitting loop in src/fitting.jl