Tandem: dual-alphabet layouts (Russian, Ukrainian, Azerbaijani) built on your optimizer

[max-hester]

Hi Dario,

I want to show you what your optimizer made possible, and to thank you for it properly.

Over the past year I have used keyboard_layout_optimizer to build dual-alphabet layouts: one set of physical keys carrying a phonetically paired letter of each script (Latin A and Cyrillic А on the same key), optimized together over a mixed-script corpus. The trick that makes it work is one you built: the Neo layout generator moves each key's whole layer stack during permutation, so a Latin-Cyrillic pairing authored into the base layout stays locked through every swap the annealer tries. Feed it real mixed-script ngrams instead of a single language and the optimizer sees the true combined load per key. No engine surgery required for the core idea. That is a testament to how well the thing is designed.

The results are now public, engine and all: https://github.com/max-hester/tandem-optimizer

Three finished designs:

• Тандем (Russian + English, 70/30 mix): cost 231.7 over 2,700 runs. Against ЙЦУКЕН, same-finger bigrams fall from 19.7% to 3.0% and hand alternation rises to 76%. The same physical layout also beats QWERTY on English. Whole natural sentences in both languages type without leaving the home row.
• ridna (Ukrainian + English, 70/30 mix): cost 290.6, shipped as Windows/macOS/Linux installers in dual-alphabet, Ukrainian-only, and UA+EN variants.
• Vəhdət (Azerbaijani + Turkish + English Latin, plus Russian Cyrillic, 60/5/20/15 mix): four languages on one layout, cost 358.41, with 1.4% same-finger bigrams in Azerbaijani and the high-frequency ə on the home row.

What the repo adds on top of upstream, in case any of it is useful to you or others here:

• a finger_travel bigram metric (Euclidean fingertip travel via Key::position.distance), registered alongside the existing bigram metrics
• the mixed-script recipe: config conventions for six-layer dual-script keys, with the secondary script on layers 4/5 behind a lock modifier so the alphabet toggle is charged only at actual script switches
• one hard-won config lesson: layers without a modifiers entry are silently dropped from evaluation (layout.rs takes modifiers.len() + 1 layers), which can turn a dual-script run into a primary-only one without any error. Defining a modifier entry per layer fixes it. Happy to write this up as a docs PR if you want it.
• retuned evaluation profiles for Russian, Ukrainian, and Azerbaijani, a Leipzig-plus-news corpus scraper, and a memo/visualization pipeline (the finger-movement renderings adapt Arne Babenhauserheide's evolve-keyboard-layout graphics; his cost model was our independent cross-check throughout)

Everything is GPL-3, same as upstream. Thank you for building and maintaining this. It is the best tool in the field, and it just carried three languages' worth of new layouts from idea to installers.

Max