Dual-Numbers Reverse AD for Functional Array Languages
Fuente:
arXiv
Saved in:
| Main Authors: | , , , |
|---|---|
| Format: | Preprint |
| Published: |
2025
|
| Subjects: | |
| Online Access: | |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| _version_ | 1866911061165211648 |
|---|---|
| author | Smeding, Tom Konarski, Mikołaj Jones, Simon Peyton Fitzgibbon, Andrew |
| author_facet | Smeding, Tom Konarski, Mikołaj Jones, Simon Peyton Fitzgibbon, Andrew |
| contents | The standard dual-numbers construction works well for forward-mode automatic differentiation (AD) and is attractive due to its simplicity; recently, it also has been adapted to reverse-mode AD, but practical performance, especially on array programs, leaves a lot to be desired. In this paper we introduce first-class support for multidimensional arrays in dual-numbers reverse-mode AD with little to no performance overhead. The algorithm consists of three loosely-coupled components: a semantics-preserving vectorisation code transformation (the bulk-operation transform or BOT), a fairly straightforward lifting of the basic dual-numbers reverse AD algorithm to a mostly first-order array language, and symbolic interpretation to achieve an end-to-end compilation pipeline. Unfortunately, we lose some of the nice generalisable aspects of dual-numbers AD in the process, most importantly support for higher-order code.
We do support some higher-order array combinators, but only a carefully-chosen set: 'build' (elementwise array construction), 'gather' and 'scatter'. In return, the BOT can eliminate the essential (for AD) higher-orderness of the input program, meaning that AD gets essentially presented with a first-order program. This allows the naive trick of lifting dual numbers to "dual arrays" to work without much modification. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2507_12640 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Dual-Numbers Reverse AD for Functional Array Languages Smeding, Tom Konarski, Mikołaj Jones, Simon Peyton Fitzgibbon, Andrew Programming Languages The standard dual-numbers construction works well for forward-mode automatic differentiation (AD) and is attractive due to its simplicity; recently, it also has been adapted to reverse-mode AD, but practical performance, especially on array programs, leaves a lot to be desired. In this paper we introduce first-class support for multidimensional arrays in dual-numbers reverse-mode AD with little to no performance overhead. The algorithm consists of three loosely-coupled components: a semantics-preserving vectorisation code transformation (the bulk-operation transform or BOT), a fairly straightforward lifting of the basic dual-numbers reverse AD algorithm to a mostly first-order array language, and symbolic interpretation to achieve an end-to-end compilation pipeline. Unfortunately, we lose some of the nice generalisable aspects of dual-numbers AD in the process, most importantly support for higher-order code. We do support some higher-order array combinators, but only a carefully-chosen set: 'build' (elementwise array construction), 'gather' and 'scatter'. In return, the BOT can eliminate the essential (for AD) higher-orderness of the input program, meaning that AD gets essentially presented with a first-order program. This allows the naive trick of lifting dual numbers to "dual arrays" to work without much modification. |
| title | Dual-Numbers Reverse AD for Functional Array Languages |
| topic | Programming Languages |
| url | https://arxiv.org/abs/2507.12640 |