128 lines
4.6 KiB
Markdown
128 lines
4.6 KiB
Markdown
# CLAUDE.md
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This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
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## Project Overview
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Fortran stellar atmosphere modeling suite being refactored to Rust. Strategy: **split Fortran into modules first, then incrementally rewrite in Rust**.
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- **TLUSTY 208**: Non-LTE stellar atmosphere calculator (~50,000 lines → 304 modules)
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- **SYNSPEC 54**: Synthetic spectrum evaluator (~24,000 lines → 168 modules)
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- **Progress**: 120/~472 Fortran units translated to Rust
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## Environment Variables
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```bash
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export TL208=/home/fmq/program/tlusty
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export TLUSTY=$TL208/tl208-s54
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export LINELIST=$TL208/linelist
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export IRON=$TL208/irondata
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export OPTABLES=$TL208/optables
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```
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## Build Commands
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### Rust
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```bash
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cargo build # Debug build
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cargo build --release # Release build
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cargo test # Run all tests (includes Fortran comparison tests)
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cargo test test_expo # Run specific test
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```
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### Fortran
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```bash
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# Production (single file)
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gfortran -O3 -fno-automatic -mcmodel=large -o tlusty/tlusty.exe tlusty/tlusty208.f
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gfortran -O3 -fno-automatic -mcmodel=large -o synspec/synspec.exe synspec/synspec54.f
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# Development (modular)
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cd rust/tlusty/extracted && make # Output: build/tlusty_extracted
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```
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**Fortran compile flags:**
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- `-mcmodel=large`: Required for large COMMON blocks (>2GB address space)
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- `-fno-automatic`: Static storage (old Fortran compatibility)
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- **Never use** `-ffixed-line-length-none`: Breaks columns 73-80 handling
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## Rust Architecture
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```
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src/
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├── lib.rs # Module exports
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├── data.rs # Static data arrays (translated from BLOCK DATA)
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├── math/ # Pure math functions (no COMMON dependency) - 120 modules
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│ ├── expint.rs # Exponential integrals
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│ ├── voigt.rs # Voigt profile
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│ ├── tridag.rs # Tridiagonal solver
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│ └── ...
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├── state/ # COMMON block translations as structs
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│ ├── constants.rs # Physical/math constants, array dimensions
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│ ├── config.rs # Runtime config
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│ ├── atomic.rs # Atomic/ion/level data
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│ ├── model.rs # Atmosphere model state (largest struct)
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│ ├── arrays.rs # Main linear equation arrays
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│ ├── iterat.rs # Iteration control
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│ ├── alipar.rs # ALI (Accelerated Lambda Iteration) arrays
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│ └── odfpar.rs # ODF (Opacity Distribution Function) data
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└── physics/ # Physics calculations (placeholder)
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```
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## Running Tests
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### Rust Tests
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```bash
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cargo test # All unit tests
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cargo test --test fortran_comparison # Fortran comparison tests only
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```
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### Fortran Integration Tests
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```bash
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# TLUSTY: H-He model test
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cd $TLUSTY/tests/tlusty/hhe
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$TLUSTY/tlusty/tlusty.exe < hhe35lt.5 > hhe35lt.6
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cp fort.7 hhe35lt.7
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diff hhe35lt.7 hhe35lt.7.bak
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# SYNSPEC: spectrum test
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cd $TLUSTY/tests/synspec/hhe
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ln -sf $TLUSTY/data data
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cp hhe35nl.7 fort.8
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ln -sf fort.55.con fort.55
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$TLUSTY/synspec/synspec.exe < hhe35nl.5
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```
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## Refactoring Workflow
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1. **Find pure functions**: Check `rust/tlusty/extracted/_PURE_UNITS.txt` for units without COMMON dependencies
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2. **Translate**: Create `src/math/<name>.rs`, add to `src/math/mod.rs`
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3. **Verify**: Add test case in `tests/fortran_comparison.rs` with Fortran reference values
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## Key Architecture
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**TLUSTY COMMON blocks** (mapped to `src/state/` structs):
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- `BASICS.FOR` → `constants.rs`: Array dimensions (`MDEPTH`=100, `MFREQ`=135000, `MLEVEL`=1134)
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- `ATOMIC.FOR` → `atomic.rs`: Atomic masses, abundances, energy levels
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- `MODELQ.FOR` → `model.rs`: Temperature, density, populations
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- `ARRAY1.FOR` → `arrays.rs`: Main linear equation arrays
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**SYNSPEC** reads model atmosphere from `fort.8`, outputs spectrum to `fort.7`
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## Fortran → Rust Translation Notes
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Critical patterns to avoid mistakes:
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- **Index conversion**: Fortran 1-indexed → Rust 0-indexed. `arr(i)` → `arr[i-1]`, `DO I=1,N` → `for i in 0..n`
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- **Expression precedence**: `-LOG(X)` is `-(LOG(X))`, not `LOG(-X)`
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- **Decrementing loops**: Use `isize`/`i32` when loop variable may become negative
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- **COMMON dependency**: Check INCLUDE statements before assuming a function is pure
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- **Large structs**: Functions with many COMMON dependencies use lifetime structs:
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```rust
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pub struct Params<'a> {
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pub input: &'a [f64],
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pub output: &'a mut [f64],
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}
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```
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- **Type inference**: `(z1 - z2).powi(2)` may fail; use `(z1 - z2) * (z1 - z2)`
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- **Test tolerance**: Polynomial approximations (Abramowitz-Stegun) need relaxed tolerance (~1e-7)
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