Function Domain/Range Analyzer implementation

Binding contract

This record describes what an executable surface must bind and validate. It does not claim that a public calculator, package, or production route is deployed.

Record owner

Guth Instruments

Lifecycle

verified-clean

Evidence ID

t8-035

Effect

Computation or source lookup only

Input and validation requirements

• Division by zero can occur if a sampler evaluates a rational function at an excluded denominator root.
• Logarithm evaluation must reject argument≤0 and must validate the base when a non-natural base is supplied.
• Even-root evaluation must reject negative radicands; odd roots do not have the same restriction.
• Floating-point tolerance near zeros, poles, and interval endpoints can incorrectly include or exclude domain points.
• Sampling finite windows cannot establish behavior as x approaches infinity or a pole.
• Periodic functions require symbolic periodicity or a justified global analysis; finite sampling can miss extrema and discontinuities.
• Removable discontinuities can be lost if expressions are algebraically simplified before domain restrictions are retained.
• The implementation needs a deterministic sampling specification and must label sampled ranges as estimates rather than exact results.

Required corrections

No binding erratum is attached to this unique-name record. Implementers must still preserve the declared units, domain, and failure behavior.

Inspectable interface fixture

The sample below is evidence for interface and validation tests, not a production implementation.

{
  "inputs": {
    "function": "(2*x + 1)/(x - 3)"
  },
  "expected_outputs": {
    "canonical_domain": "(-∞, 3) ∪ (3, ∞)",
    "canonical_range": "(-∞, 2) ∪ (2, ∞)",
    "estimated_range": "Sampling-dependent; the exact range is (-∞, 2) ∪ (2, ∞).",
    "restrictions": [
      "x - 3 ≠ 0",
      "x ≠ 3"
    ],
    "spot_checks": [
      {
        "at": 0,
        "input_side": -0.3333333333,
        "answer_side": -0.3333333333
      },
      {
        "at": 4,
        "input_side": 9,
        "answer_side": 9
      }
    ]
  },
  "reference_data": {
    "range_derivation": "Let y=(2x+1)/(x-3). Then y(x-3)=2x+1, so x(y-2)=3y+1. For y=2 this gives 0=7, impossible; every other real y has x=(3y+1)/(y-2)."
  },
  "working": "Domain: set the denominator nonzero: x-3≠0, so x≠3. Domain is (-∞,3)∪(3,∞). Range: solve y=(2x+1)/(x-3). Multiply: yx-3y=2x+1. Rearrange: x(y-2)=3y+1. If y=2, the equation becomes 0=7, impossible. If y≠2, x=(3y+1)/(y-2) is real, so every y except 2 occurs. Therefore range is (-∞,2)∪(2,∞). Spot check at x=0: (2·0+1)/(0-3)=1/(-3)=-1/3=-0.3333333333. Spot check at x=4: (2·4+1)/(4-3)=9/1=9."
}

Other records

Sources and evidence

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

• VERIFIED_LEDGER.json
• evidence-tranche8/tranche8-results.json