---
title: "langseg-engine-viterbi — Mova code model"
description: "Mova code model of tools/langseg/src/lib.rs: components with their labels, obernants and the model text."
url: "https://groupants.elamur.ai/free/en/mova/tools/langseg/src/lib.rs.groupant/viterbi.groupant/"
---
Elamur: [Mova](https://md.mova.elamur.ai/free/en/) · [Dictionary](https://md.dictionary.elamur.ai/free/en/) · [Research](https://md.research.elamur.ai/free/en/) · **Groupants**

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# langseg-engine-viterbi

The groupant beside tools/langseg/src/lib.rs in the Mova repository: what the code computes, what it never does, how to go back from its outputs, its invariants, cost and checks.

## Facts

- **kind:** groupant_fragment
- **status:** partial source bound model
- **source:** [`tools/langseg/src/lib.rs`](https://github.com/ElamurAI/mova-free/blob/main/tools/langseg/src/lib.rs)
- **source SHA-256:** `33431b9d2b514927…`
- **covers:** best=scores0; choose stay vs global top-cost with backpointers, final argmax/backtrace. (bytes 19169–20095)
- **part of:** [langseg-engine](https://md.groupants.elamur.ai/free/en/mova/tools/langseg/src/lib.rs.groupant/)
- **repository folder:** [`tools/langseg/src/lib.rs.groupant/viterbi.groupant`](https://github.com/ElamurAI/mova-free/tree/main/tools/langseg/src/lib.rs.groupant/viterbi.groupant)
- **repository commit:** `855da7bd4a7b`

> **Implementation material.** A Mova code model describes this code at one source revision: partial models, finite checks and their stated scope. It is not a reviewed general exposition, and its labels are shown as written, never raised.

## Components

| component | label | where |
|---|---|---|
| **approximant** | partial | [approximant](#approximant) |
| **ast** | partial | `../syntax.json` |
| **cost** | symbolic source derived | [invariant](#invariant) |
| **descriptant** | present | [descriptant](#descriptant) |
| **invariant** | partial | [invariant](#invariant) |
| **tests** | executed bounded checks | [tests](#tests) |

## Obernants

The typed relations around the forward model: the behaviour complement (what the code never does), the reverse reconstruction (every input compatible with an output) and specialised views.

| id | type | label | where |
|---|---|---|---|
| `behavior_complement` | behavior_complement | partial source derived model | [behavior_complement](#behavior-complement) |
| `reverse_reconstruction` | reverse_reconstruction | partial source derived model | [reverse_reconstruction](#reverse-reconstruction) |
| `objective` | objective | partial source derived model | [objective](#objective) |
| `ties` | ties | partial source derived model | [ties](#ties) |
| `empty` | empty | partial source derived model | [empty](#empty) |
| `backtrace` | backtrace | partial source derived model | [backtrace](#backtrace) |

## Model text


### descriptant

#### Descriptant

##### Prospective epoch

2026-10-31 source review predicted: best=scores0; choose stay vs global top-cost with backpointers, final argmax/backtrace. Resource model: O(nK) time/storage K8. External prospective.md predates test additions and preserves APIs, effect order, hazards and interaction hypotheses.

##### Observed epoch

Bounded real helper checks in tests.md constrain these models; syntax is a partial lexical projection with no macro expansion, name resolution or proof. Production expressions unchanged; five inline test modules added. Compiled mutants are temporary and exactly restored. Existing malformed-input and nonfinite domains remain explicit, not silently repaired. Parent composes this scope with siblings without adding overlapping costs twice.

Exact byte scope; finite correspondence only. Untested branches source-derived.

### approximant

#### Forward relation

best=scores0; choose stay vs global top-cost with backpointers, final argmax/backtrace.

Domain: Empty returns before cost access; cost.len>=n for nonempty; stay ties and lowest final index.

### invariant

#### Invariant and cost

##### Invariant

Empty returns before cost access; cost.len>=n for nonempty; stay ties and lowest final index.

##### Cost

O(nK) time/storage K8.

##### Limits

Exact byte scope; finite correspondence only. Untested branches source-derived. No percentage surrogate is implemented: categorical parsing/effect observations lack an admitted numerical error metric. Any future profile must define its metric/domain and use only1/2/5/10 percent caps.

### models

## Typed source-bound relations

Subject: exact source SHA-256 in manifest. Domain and resource premises are in invariant.md. Each model is partial, source-derived, over a single helper invocation or the described finite trace. Complements are proposed inner exclusions under those premises; reverse relations retain all compatible antecedents, with no unique inverse claim. The oracle is the named checks in tests.md; unexecuted cases remain hypotheses. No numerical approximation certificate.

### behavior_complement

No out-of-range columns; finite nonnegative switches cannot reward switching.

### reverse_reconstruction

Path admits score/cost inequalities, not unique logits.

### objective

Nonnegative cost makes discounted same-column jump dominated by stay, justifying O(K) shortcut.

### ties

stay>=jump retains k, final argmax strict greater retains lowest.

### empty

Empty scores/empty costs returns[]; single row never reads cost0.

### backtrace

path[n-1]=argmax(best); path[i-1]=back[i][path[i]], n states.

### tests

#### Checks and evidence

Named source/helper checks: wave31::empty_ties_and_switch_objective, viterbi_cuts_a_planted_sentence_and_only_with_a_finite_switch.

Wave31 on2026-10-31:30 distinct exact tests passed twice debug and twice release, with equal sorted named outcomes. This node claims only its listed subset; empty subset means source review only. Six actual source-behavior mutants compiled, failed assertions, restored exact bytes/hash, and passed focused green reruns. No assertion-only mutants; existing swapped-input controls are separate. Receipt bundle: $MOVA_DATA/runs/octopus-wave31-corpus-2026-10-31 (native-commands.json, source-test-map.json, mutation-results.json, *.status/*.log). No live corpus, teacher, frozen assessment, download or production data used.

Exact byte scope; finite correspondence only. Untested branches source-derived.