Introduction

matten is a developer-experience-first multidimensional array (tensor) library for Rust — the family car for learning, teaching, small numerical workflows, data exploration, and early prototypes.

Maturity labels in this book — such as production-ready — describe stability within that scope, not performance or scale. matten optimizes for time to first understanding and a runnable PoC, not benchmark leadership.

This book is organized by reader:

• New users — philosophy and a quick start.
• Playground — try broadcasting, reshape, axis reductions, and matmul in the browser, no install required: Playground.
• Reference — the rules that shape the public API.
• Contributors — project layout, milestones, and process.

This documentation tracks the current 0.46 release family, carrying RFC-110, RFC-111, and RFC-112 — no new API, only behaviour changes and a restriction removed. Zero-sized dimensions are now constructible directly (Tensor::try_new(vec![], &[0, 3]) succeeds), not merely reachable by slicing as before: every constructor, reshape, the shape-composition family, linspace/eye, serde, and the matten-ndarray bridge accept them. Display on an empty tensor now shows its shape instead of an empty string; Debug is unchanged. mean_axis/min_axis/max_axis/var_axis/std_axis now error when the reduced axis has length 0, instead of leaking NaN/inf/ -inf — a zero-length surviving axis is a different case and was and remains Ok with an empty result; sum/sum_axis are unchanged, their additive identity was already correct. matten-ndarray’s ZeroSizedAxis error variant is deprecated and never constructed, kept only so existing code matching on it still compiles. matten-mlprep’s standardize_columns/minmax_scale_columns return a different error — not a different outcome — for a zero-row input: previously a shape-rejection error from tensor construction, now an axis-reduction error, both Err, never a panic in any released version — see the [0.46.0] CHANGELOG entry for the complete list.