`61d382f`

feat(control): reject near-orthogonal sign alignment in extract_control_vector

Authored by

espadonne 3 weeks ago

SHA: 61d382f6fe01f1689331bbc5190b21ce1eab440b
Parents: d12f6a7
Tree: eb5fa4d

1 changed file

Status	File	+	-
M	`src/dlm/control/extract.py`	26	1

src/dlm/control/extract.pymodified

  from dlm.control.errors import ControlExtractError, ControlPolicyRefusal
 +# Minimum |cos(angle)| between principal SVD direction and mean(diffs)
 +# for the sign-alignment step to be meaningful. 0.1 is a practical
 +# "loosely aligned" floor — below it, the mean pull is essentially
 +# orthogonal to the direction and the sign flip is dominated by noise.
 +_SIGN_ALIGN_THRESHOLD: float = 0.1
++
  @dataclass(frozen=True)
  class ControlVector:
      # is unique only up to sign), which would make extraction
      # non-reproducible across numpy versions. Convention: positive
      # strength pushes toward chosen, so align with mean(diffs).
 +    #
 +    # Threshold check: when the principal direction is near-orthogonal
 +    # to the mean pull, |cos(angle)| is near zero and the sign decision
 +    # is dominated by numerical noise — two runs on slightly different
 +    # data would produce opposite signs. That's a meaningless vector,
 +    # not a steering direction; reject rather than ship a coin-flip.
      mean_pull = diffs.mean(axis=0)
 -    if float(np.dot(direction, mean_pull)) < 0:
 +    mean_pull_norm = float(np.linalg.norm(mean_pull))
 +    dot = float(np.dot(direction, mean_pull))
 +    if mean_pull_norm > 0.0:
 +        cos_align = abs(dot) / mean_pull_norm  # direction is already unit-length
 +        if cos_align < _SIGN_ALIGN_THRESHOLD:
 +            raise ControlExtractError(
 +                "principal SVD direction is near-orthogonal to mean(diffs) "
 +                f"(|cos|={cos_align:.3f} < {_SIGN_ALIGN_THRESHOLD}). "
 +                "This means the preference pairs disagree enough that the "
 +                "sign of the extracted direction is unstable — two runs on "
 +                "similar data would emit opposite vectors. Gather more "
 +                "coherent pairs or check that chosen/rejected are not swapped."
 +            )
 +    if dot < 0:
          direction = -direction
      explained = float(singular_values[0] ** 2 / total_energy)