Explaining Missing Simulink Coverage

Explain why coverage objectives are missing on a coverage result the user already has, and what to do about each one — across all objective types (decision, condition, MCDC, relational boundary, saturation/overflow, lookup-table execution). Works from an existing cvdata / cvdatagroup, a .cvt file, a Simulink.SimulationOutput with coverage on, or a Simulink Test result set.

It keeps two questions separate:

• Is this outcome reachable? — for decision/condition/MCDC objectives, answered by formal proof (SLDV dead-logic detection) joined to the coverage result deterministically. A provably-dead outcome is a fact.
• If reachable, why wasn't it tested — and if dead, was that intended? — answered by the agent, reasoning over an input trace (Model Slicer) plus model structure. This is judgment, always presented as a recommendation.

Requires: MATLAB R2023a+, Simulink Coverage, Simulink Design Verifier (dead-logic detection), Simulink Check / Model Slicer (input tracing). The skill never collects coverage — it reads a result that already exists. When SLDV or the Model Slicer is unavailable, the affected step degrades honestly (see Guardrails), never fabricating evidence.

When to Use

• User asks why an objective — of any metric — or a specific true/false outcome is missing, unsatisfied, or uncovered.
• User asks whether uncovered logic is dead code (unreachable) or just untested.
• User asks how to close a coverage gap on a result they already collected — what test to add, what to filter, or what to change.
• User needs audit-ready triage: provably-dead vs. still-to-test, each traced to its inputs.
• User points at an existing coverage artifact and asks to explain it.

When NOT to Use

• Collecting coverage / simulating to measure coverage → this skill reads a result, it does not collect one; tell the user to collect coverage first, then return here.
• Authoring or generating tests → testing-simulink-models. This skill recommends a scenario in words; it does not build a harness or generate vectors.
• Design-error detection / fixing runtime defects (divide-by-zero, overflow) → resolve-design-errors.
• Model compliance against a standard (MISRA, MAB, JMAAB) → checking-model-compliance.
• Requirement verification → not this skill (it only queries existing links, read-only).

Coverage Sources

All four sources resolve to the one object the analysis consumes — a cvdata / cvdatagroup. resolveCoverageData normalizes them and makes no decisions; when a source carries more than one unit, the agent asks which to explain.

Source	Holds	Resolves via
cvsim result	cvdata / cvdatagroup	pass through
.cvt file	path	cvload (cell of cvdata)
sim w/ coverage	SimulationOutput	embedded cvdata var, else cvresults(model) (per-run + cumulative)
Simulink Test	ResultSet	getCoverageResults (cvdata object array)

Rules the agent applies: multiple units → always ask which to explain (never merge or pick silently); cvresults per-run vs. cumulative → cumulative by default, mention the single-run view exists.

Prerequisites

All script functions live in the skill's scripts/ directory. Call them with evaluate_matlab_code and project_path set to that folder. Never addpath, restoredefaultpath, or savepath — altering the session path breaks the coverage tooling.

Use these functions; do not hand-roll resolution, extraction, the SLDV run, the join, or the trace. The Step-2 join in particular matches SLDV verdicts to outcomes on an exact key — the agent must never do that matching itself.

Function	Inputs → Output	Role
resolveCoverageData(source)	source → {cvdata,model,kind,label}[]	Normalize sources to a list of units
getCoverageSummary(cvd)	one cvdata → covSummary	Rollups + outcome detail + filter/reduced info
detectDeadLogicObjectives(model, metrics)	model + metrics → [dead, status]	SLDV dead-logic (decision/condition/MCDC only)
markSldvDeadLogic(covSummary, dead)	covSummary + dead → covSummary	Deterministic join — stamp dead, record unmatched/contradictions
traceObjectiveInputs(model, blockPaths, maxDepth)	model + paths → [traces, status]	Slicer: controllable inputs + dependency chain

The scripts return MATLAB structs. Their exact output contracts — field names, nesting, what an absent field means — are documented in references/script-outputs.md; consume the returns by that reference rather than probing fieldnames and guessing paths. Deeper method detail lives in references (load on demand): SLDV recipe + join semantics in references/dead-logic-analysis.md; classification + scenario composition in references/explaining-and-resolving.md; filter authoring in references/coverage-filter-api.md (load after filter approval, Step 3); read-only requirement traceability in references/requirements-tracing.md (load when prioritizing by requirement linkage, Step 3).

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Workflow

Three steps. Step 1 is cheap and always safe; Steps 2–3 run the expensive engines and are gated — do not run them for a plain "summarize" request.

1. Summarize coverage       → resolveCoverageData + getCoverageSummary
2. Locate missing objectives → collect uncovered outcomes; if any decision/condition/MCDC
                              are uncovered, detectDeadLogicObjectives + markSldvDeadLogic
3. Explain and resolve      → traceObjectiveInputs on the owning blocks; agent explains

Step 1 — Summarize coverage

1. cands = resolveCoverageData(source). The source's model must be loaded first — if it isn't open or on the path, load_system it (not addpath). If numel(cands) > 1, ask which unit(s) to explain. For a sim yielding per-run and cumulative, default to cumulative and say so.
2. covSummary = getCoverageSummary(cands(k).cvdata).
3. Render a summary: total satisfied / total, then a worst-first table of systems by unsatisfied count (kind == 'system' nodes — the model root and each subsystem/chart, not subsystems only; omit fully-covered ones). Name the enabled metrics.

Gate. Stop here unless the user asked why coverage is missing or how to improve it.

Step 2 — Locate missing objectives

1. Collect the uncovered Tier-2 outcomes (covered == false). If none, STOP — report full coverage on the enabled metrics.
2. Run SLDV only if at least one uncovered outcome is decision / condition / MCDC (the metrics SLDV dead-logic covers). Otherwise skip it and go to Step 3.
3. If running it:

   [dead, status] = detectDeadLogicObjectives(model, metrics);   % dead-eligible metrics present
   covSummary = markSldvDeadLogic(covSummary, dead);                    % exact-key join; do NOT match by hand
   

4. Present the outcomes in their reachability states (detail in references/dead-logic-analysis.md):
   • Provably dead — SLDV ran and the join stamped dead == true (fact).
   • Reachable, stated cautiously — decision/condition/MCDC, SLDV ran, not stamped dead: "SLDV found no dead logic here, so it needs a test." Not a completeness proof.
   • Deadness not established — SLDV skipped_no_license / error, or a non-SLDV-analyzable metric (relational / saturation / lookup-table). State the reason.

Step 3 — Explain and resolve

Trace the owning blocks of the uncovered outcomes in one batch, then reason over the evidence (full method in references/explaining-and-resolving.md):

[traces, status] = traceObjectiveInputs(model, blockPaths);

• Judge intent from the traced evidence — the controllable inputs and what each block in the chain computes. A control pinned by a Constant/configuration, or a defensive guard the trace shows can't be reached in this context (a range clamp, a divide-by-zero guard) → likely intentional (recommend a coverage filter, Justify mode — references/explaining-and-resolving.md, references/coverage-filter-api.md). A dead branch tracing to controllable inputs → likely unintentional (recommend a design review). When the trace leaves intent unclear, use model_read / model_overview for more context.
• Compose a test scenario for testable outcomes: invert the required condition from the chain (Switch y = (u2 >= 5) ? …, false uncovered → drive u2 < 5), stated in the controllable inputs. Group outcomes sharing inputs — one test often closes several.
• When a trace is method == "unavailable", fall back to model_read / model_overview on that block; never fabricate inputs or a chain.
• When prioritizing which outcomes to test first — or whenever the user asks what to address first — check requirement linkage (read-only, references/requirements-tracing.md) if Requirements Toolbox is available: a linked + uncovered outcome is "untested but required" (cite the requirement ID) and outranks an unlinked one; an unlinked outcome is lower priority (a hint the logic may be unrequired — surface it, do not conclude it). If Requirements Toolbox is unavailable, say so and prioritize without it.

Writing a .cvf filter or editing the model is Ask First (Guardrails).

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Guardrails

Always

• State the resolved unit (model, label, per-run vs. cumulative) and enabled metrics in the summary header.
• Report covSummary counts verbatim; the two coverage tiers agree by construction — do not recompute them.
• Separate fact from judgment in every finding ("SLDV proved this unreachable" vs. "this appears intentional because the control is a constant").
• Signal honestly when an engine did not run: status == "skipped_no_license" / "error" and per-block method == "unavailable" mean not performed — say so.
• Group testable outcomes by shared inputs and note when one test closes several.

Ask First

• Which unit to explain, whenever the source resolves to more than one.
• Writing a coverage filter (.cvf) — present the rule and rationale; write only on explicit approval, using the engineer's rationale (never fabricated).
• Editing the model — present the change; apply only on explicit approval, never silently to the original.

Never

• Never declare an outcome "dead code, safe to filter" as fact. SLDV proves unreachability; whether dead logic is intentional and filterable is the engineer's audit call. Present evidence + a recommendation.
• Never index-match SLDV verdicts to outcomes by hand — markSldvDeadLogic owns the join.
• Never call a completed-SLDV "no dead logic" result a completeness proof — a timeout (status == -1) can hide deadness.
• Never modify the MATLAB path (addpath / restoredefaultpath / savepath).

Common Mistakes

Mistake	Fix
Running SLDV / Slicer for a "summarize" request	Step 1 only; gate on wanting the why
Running SLDV when no decision/condition/MCDC outcome is uncovered	SLDV covers those three metrics only; skip otherwise
Reporting "provably dead" when SLDV was skipped/errored	Nothing is provably dead without a completed SLDV run
Calling non-D/C/MCDC gaps "reachable"	SLDV can't analyze them; state deadness as not established
Matching SLDV results to outcomes in the agent	Call markSldvDeadLogic; consume dead_analysis
Classifying dead logic from block names	Classify from the dependency chain + model_read
Fabricating a chain when method == "unavailable"	Fall back to model_read / model_overview
Silently picking one cvdata from many	Ask which unit to explain

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