Source: https://guthlabs.ai/docs/instruments/truss-determinacy-checker/mechanism/

instrument mechanism / verified-clean

# Truss Determinacy Checker mechanism

The inspectable method record for Truss Determinacy Checker, kept separate from implementation and qualification.

Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**

## Model scope

The exact ambiguity is whether this instrument is intended to report only the planar Maxwell count or to make a definitive structural classification. As written, it claims definitive classification but lacks assumptions and geometry/connectivity checks. Revise the honest label to something such as 'preliminary planar truss determinacy count' unless full stability and rank analysis is added.

- m+r=2j is the planar Maxwell count, not a sufficient test for determinacy, indeterminacy, or stability. Connectivity, support arrangement, member geometry, and joint geometry must also be checked.

- The formulas require an explicit planar, pin-jointed, ideal-truss assumption. A spatial truss generally uses m+r=3j instead.

- m+r>2j indicates a positive count of excess constraints only if the truss is stable and the constraints are independent; it does not by itself prove static indeterminacy.

- m+r<2j indicates a constraint deficiency or possible mechanism, but does not by itself prove instability for every geometry.

- For m+r<2j, m+r-2j is a negative deficiency/index, not technically a degree of static indeterminacy. The output definition must distinguish these.

## Units and conventions

- m, r, and j are dimensionless, nonnegative integer counts: members, independent reaction components, and joints.

- The count assumes a planar pin-jointed truss analyzed with two equilibrium equations per joint.

- Each reaction component is counted independently; a pin support normally contributes two reactions and a roller support normally contributes one in a planar model.

- No length, force, or other physical units are involved.

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "inputs": {
    "m": 3,
    "r": 3,
    "j": 3
  },
  "expected_outputs": {
    "classification": "determinate",
    "degree_of_indeterminacy": 0
  },
  "working": "m+r = 3+3 = 6. 2j = 2×3 = 6. Since 6 = 6, classification = determinate. Degree = (m+r)−2j = 6−6 = 0."
}
````

## Failure boundary

**BREAK_CLAIMED** · SELF_FLAGGED

The classifier has no division-by-zero operation, but extreme counts overflow JavaScript arithmetic and produce an infinite degree. More importantly, the meaning of r is convention-sensitive: counting supports instead of scalar reaction components can change the computed reaction count and classification unless the support model is explicitly defined.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/truss-determinacy-checker/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/truss-determinacy-checker/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/truss-determinacy-checker/qualification/>)

## Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

- `VERIFIED_LEDGER.json`

- `evidence-tranche4/tranche4-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`