la-stack

Fast, stack-allocated linear algebra for fixed dimensions in Rust.

This crate grew from the need to support delaunay with fast, stack-allocated linear algebra primitives and algorithms while keeping the API intentionally small and explicit.

📐 Introduction

la-stack provides a handful of const-generic, stack-backed building blocks:

Vector<const D: usize> for fixed-length vectors ([f64; D] today)
Matrix<const D: usize> for fixed-size square matrices ([[f64; D]; D] today)
Lu<const D: usize> for LU factorization with partial pivoting (solve + det)

✨ Design goals

✅ Const-generic dimensions (no dynamic sizes)
✅ Stack storage only (no heap allocation in core types)
✅ Copy types where possible
✅ Explicit algorithms (LU, solve, determinant)
✅ unsafe forbidden
✅ No runtime dependencies (dev-dependencies are for contributors only)

🔢 Scalar types

Today, the core types are implemented for f64. The intent is to support f32 and f64 (and f128 if/when Rust gains a stable primitive for it). Longer term, we may add optional arbitrary-precision support (e.g. via rug) depending on performance.

🚀 Quickstart

Add this to your Cargo.toml:

[dependencies]
la-stack = "0.1"

Solve a 5×5 system via LU:

use la_stack::prelude::*;

// This system requires pivoting (a[0][0] = 0), so it's a good LU demo.
// A = J - I: zeros on diagonal, ones elsewhere.
let a = Matrix::<5>::from_rows([
    [0.0, 1.0, 1.0, 1.0, 1.0],
    [1.0, 0.0, 1.0, 1.0, 1.0],
    [1.0, 1.0, 0.0, 1.0, 1.0],
    [1.0, 1.0, 1.0, 0.0, 1.0],
    [1.0, 1.0, 1.0, 1.0, 0.0],
]);

let b = Vector::<5>::new([14.0, 13.0, 12.0, 11.0, 10.0]);

let lu = a.lu(DEFAULT_PIVOT_TOL).unwrap();
let x = lu.solve_vec(b).unwrap().into_array();

// Floating-point rounding is expected; compare with a tolerance.
let expected = [1.0, 2.0, 3.0, 4.0, 5.0];
for (x_i, e_i) in x.iter().zip(expected.iter()) {
    assert!((*x_i - *e_i).abs() <= 1e-12);
}

🧩 API at a glance

Type	Storage	Purpose	Key methods
`Vector<D>`	`[f64; D]`	Fixed-length vector	`new`, `zero`, `dot`, `norm2_sq`
`Matrix<D>`	`[[f64; D]; D]`	Fixed-size square matrix	`from_rows`, `zero`, `identity`, `lu`, `det`
`Lu<D>`	`Matrix<D>` + pivot array	Factorization for solves/det	`solve_vec`, `det`

Storage shown above reflects the current f64 implementation.

📋 Examples

The examples/ directory contains small, runnable programs:

just examples
# or:
cargo run --example solve_5x5
cargo run --example det_5x5

🤝 Contributing

A short contributor workflow:

cargo install just
just ci           # lint + fast tests + bench compile
just commit-check # lint + all tests + examples

For the full set of developer commands, see just --list and WARP.md.

📄 License

BSD 3-Clause License. See LICENSE.

la-stack 0.1.0