FA-93671 / Solar tracker geometry / Open access

Overcast diffuse flat stow: diffuse threshold · case 01

At exactly the diffuse threshold the rows keep tracking.

Verified by executionVariant 1 · 7 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The threshold comparison is strict.

VERIFIED REPAIR

Go flat when df >= thresh_pct.

Unsuccessful approach: Rounding before a strict comparison still misses the threshold.

Case contract

ghi <= 0 returns [0.0, night]. Diffuse fraction df = dhi*100/ghi percent (may exceed 100 with sensor noise). df >= thresh_pct: [0.0, 'diffuse']. If blend > 0 and df > thresh_pct - blend the angle is ideal*(thresh_pct - df)/blend ('blend'). Otherwise [ideal, 'track']. Angles rounded to 3.

Why this case matters

Single-axis and dual-axis solar trackers turn a sun direction into actuator commands; a sign, frame or limit mistake points a whole plant away from the sun or into a mechanical stop.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(ghi, dhi, ideal, thresh_pct, blend):
    if ghi <= 0:
        return [0.0, 'night']
    df = dhi * 100 / ghi
    if df > thresh_pct:
        return [0.0, 'diffuse']
    if blend > 0 and df > thresh_pct - blend:
        return [round(ideal * (thresh_pct - df) / blend, 3), 'blend']
    return [round(float(ideal), 3), 'track']
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['boundary: diffuse fraction at threshold', [400, 280, 30, 70, 10], [0.0, 'diffuse']],
  ['boundary: blend band lower edge', [400, 240, 30, 70, 10], [30.0, 'track']],
  ['normal: clear sky', [800, 80, -45, 70, 10], [-45.0, 'track']],
  ['regression: diffuse threshold', [100, 80, 25, 80, 20], [0.0, 'diffuse']],
  ['regression: diffuse threshold (partial repair)', [100, 60, 45, 60, 10], [0.0, 'diffuse']],
  ['control 1', [100, 400, -30, 70, 20], [0.0, 'diffuse']],
  ['control 2', [0, 80, 0, 70, 0], [0.0, 'night']]],
 [['boundary: diffuse fraction at threshold', [400, 280, 30, 70, 10], [0.0, 'diffuse']],
  ['boundary: blend band lower edge', [400, 240, 30, 70, 10], [30.0, 'track']],
  ['normal: clear sky', [800, 80, -45, 70, 10], [-45.0, 'track']],
  ['regression: diffuse threshold', [100, 60, 45, 60, 10], [0.0, 'diffuse']],
  ['regression: diffuse threshold (partial repair)', [100, 60, 45, 60, 20], [0.0, 'diffuse']],
  ['control 1', [100, 400, -30, 70, 0], [0.0, 'diffuse']],
  ['control 2', [100, 0, 0, 70, 0], [0.0, 'track']]],
 [['boundary: diffuse fraction at threshold', [400, 280, 30, 70, 10], [0.0, 'diffuse']],
  ['boundary: blend band lower edge', [400, 240, 30, 70, 10], [30.0, 'track']],
  ['normal: clear sky', [800, 80, -45, 70, 10], [-45.0, 'track']],
  ['regression: diffuse threshold', [100, 60, 45, 60, 20], [0.0, 'diffuse']],
  ['regression: diffuse threshold (partial repair)', [100, 80, -30, 80, 20], [0.0, 'diffuse']],
  ['control 1', [200, 160, 25, 70, 0], [0.0, 'diffuse']],
  ['control 2', [800, 160, -50, 80, 20], [-50.0, 'track']]],
 [['boundary: diffuse fraction at threshold', [400, 280, 30, 70, 10], [0.0, 'diffuse']],
  ['boundary: blend band lower edge', [400, 240, 30, 70, 10], [30.0, 'track']],
  ['normal: clear sky', [800, 80, -45, 70, 10], [-45.0, 'track']],
  ['regression: diffuse threshold', [100, 80, -30, 80, 20], [0.0, 'diffuse']],
  ['regression: diffuse threshold (partial repair)', [200, 160, 25, 80, 20], [0.0, 'diffuse']],
  ['control 1', [400, 80, -30, 80, 0], [-30.0, 'track']],
  ['control 2', [0, 60, 25, 80, 0], [0.0, 'night']]],
 [['boundary: diffuse fraction at threshold', [400, 280, 30, 70, 10], [0.0, 'diffuse']],
  ['boundary: blend band lower edge', [400, 240, 30, 70, 10], [30.0, 'track']],
  ['normal: clear sky', [800, 80, -45, 70, 10], [-45.0, 'track']],
  ['regression: diffuse threshold', [200, 160, 25, 80, 20], [0.0, 'diffuse']],
  ['regression: diffuse threshold (partial repair)', [100, 80, -50, 80, 0], [0.0, 'diffuse']],
  ['control 1', [400, 400, 0, 80, 10], [0.0, 'diffuse']],
  ['control 2', [100, 400, -30, 70, 0], [0.0, 'diffuse']]]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
boundary: diffuse fraction at threshold	`[0.0, 'blend']`	`[0.0, 'diffuse']`	Failed
boundary: blend band lower edge	`[30.0, 'track']`	`[30.0, 'track']`	Passed
normal: clear sky	`[-45.0, 'track']`	`[-45.0, 'track']`	Passed
regression: diffuse threshold	`[0.0, 'blend']`	`[0.0, 'diffuse']`	Failed
regression: diffuse threshold (partial repair)	`[0.0, 'blend']`	`[0.0, 'diffuse']`	Failed
control 1	`[0.0, 'diffuse']`	`[0.0, 'diffuse']`	Passed
control 2	`[0.0, 'night']`	`[0.0, 'night']`	Passed

SHA-256 / 1f185a83c4f7cd7c35df185b6a47c4ef767f393e03577a6b53fdd458450ad814

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(ghi, dhi, ideal, thresh_pct, blend):
    if ghi <= 0:
        return [0.0, 'night']
    df = dhi * 100 / ghi
    if round(df) > thresh_pct:
        return [0.0, 'diffuse']
    if blend > 0 and df > thresh_pct - blend:
        return [round(ideal * (thresh_pct - df) / blend, 3), 'blend']
    return [round(float(ideal), 3), 'track']
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['boundary: diffuse fraction at threshold', [400, 280, 30, 70, 10], [0.0, 'diffuse']],
  ['boundary: blend band lower edge', [400, 240, 30, 70, 10], [30.0, 'track']],
  ['normal: clear sky', [800, 80, -45, 70, 10], [-45.0, 'track']],
  ['regression: diffuse threshold', [100, 80, 25, 80, 20], [0.0, 'diffuse']],
  ['regression: diffuse threshold (partial repair)', [100, 60, 45, 60, 10], [0.0, 'diffuse']],
  ['control 1', [100, 400, -30, 70, 20], [0.0, 'diffuse']],
  ['control 2', [0, 80, 0, 70, 0], [0.0, 'night']]],
 [['boundary: diffuse fraction at threshold', [400, 280, 30, 70, 10], [0.0, 'diffuse']],
  ['boundary: blend band lower edge', [400, 240, 30, 70, 10], [30.0, 'track']],
  ['normal: clear sky', [800, 80, -45, 70, 10], [-45.0, 'track']],
  ['regression: diffuse threshold', [100, 60, 45, 60, 10], [0.0, 'diffuse']],
  ['regression: diffuse threshold (partial repair)', [100, 60, 45, 60, 20], [0.0, 'diffuse']],
  ['control 1', [100, 400, -30, 70, 0], [0.0, 'diffuse']],
  ['control 2', [100, 0, 0, 70, 0], [0.0, 'track']]],
 [['boundary: diffuse fraction at threshold', [400, 280, 30, 70, 10], [0.0, 'diffuse']],
  ['boundary: blend band lower edge', [400, 240, 30, 70, 10], [30.0, 'track']],
  ['normal: clear sky', [800, 80, -45, 70, 10], [-45.0, 'track']],
  ['regression: diffuse threshold', [100, 60, 45, 60, 20], [0.0, 'diffuse']],
  ['regression: diffuse threshold (partial repair)', [100, 80, -30, 80, 20], [0.0, 'diffuse']],
  ['control 1', [200, 160, 25, 70, 0], [0.0, 'diffuse']],
  ['control 2', [800, 160, -50, 80, 20], [-50.0, 'track']]],
 [['boundary: diffuse fraction at threshold', [400, 280, 30, 70, 10], [0.0, 'diffuse']],
  ['boundary: blend band lower edge', [400, 240, 30, 70, 10], [30.0, 'track']],
  ['normal: clear sky', [800, 80, -45, 70, 10], [-45.0, 'track']],
  ['regression: diffuse threshold', [100, 80, -30, 80, 20], [0.0, 'diffuse']],
  ['regression: diffuse threshold (partial repair)', [200, 160, 25, 80, 20], [0.0, 'diffuse']],
  ['control 1', [400, 80, -30, 80, 0], [-30.0, 'track']],
  ['control 2', [0, 60, 25, 80, 0], [0.0, 'night']]],
 [['boundary: diffuse fraction at threshold', [400, 280, 30, 70, 10], [0.0, 'diffuse']],
  ['boundary: blend band lower edge', [400, 240, 30, 70, 10], [30.0, 'track']],
  ['normal: clear sky', [800, 80, -45, 70, 10], [-45.0, 'track']],
  ['regression: diffuse threshold', [200, 160, 25, 80, 20], [0.0, 'diffuse']],
  ['regression: diffuse threshold (partial repair)', [100, 80, -50, 80, 0], [0.0, 'diffuse']],
  ['control 1', [400, 400, 0, 80, 10], [0.0, 'diffuse']],
  ['control 2', [100, 400, -30, 70, 0], [0.0, 'diffuse']]]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
boundary: diffuse fraction at threshold	`[0.0, 'blend']`	`[0.0, 'diffuse']`	Failed
boundary: blend band lower edge	`[30.0, 'track']`	`[30.0, 'track']`	Passed
normal: clear sky	`[-45.0, 'track']`	`[-45.0, 'track']`	Passed
regression: diffuse threshold	`[0.0, 'blend']`	`[0.0, 'diffuse']`	Failed
regression: diffuse threshold (partial repair)	`[0.0, 'blend']`	`[0.0, 'diffuse']`	Failed
control 1	`[0.0, 'diffuse']`	`[0.0, 'diffuse']`	Passed
control 2	`[0.0, 'night']`	`[0.0, 'night']`	Passed

SHA-256 / 48f95cc698e5014116d674cc6c1498ad3be676b8e65910237a0a5efbd770178e

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(ghi, dhi, ideal, thresh_pct, blend):
    if ghi <= 0:
        return [0.0, 'night']
    df = dhi * 100 / ghi
    if df >= thresh_pct:
        return [0.0, 'diffuse']
    if blend > 0 and df > thresh_pct - blend:
        return [round(ideal * (thresh_pct - df) / blend, 3), 'blend']
    return [round(float(ideal), 3), 'track']
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['boundary: diffuse fraction at threshold', [400, 280, 30, 70, 10], [0.0, 'diffuse']],
  ['boundary: blend band lower edge', [400, 240, 30, 70, 10], [30.0, 'track']],
  ['normal: clear sky', [800, 80, -45, 70, 10], [-45.0, 'track']],
  ['regression: diffuse threshold', [100, 80, 25, 80, 20], [0.0, 'diffuse']],
  ['regression: diffuse threshold (partial repair)', [100, 60, 45, 60, 10], [0.0, 'diffuse']],
  ['control 1', [100, 400, -30, 70, 20], [0.0, 'diffuse']],
  ['control 2', [0, 80, 0, 70, 0], [0.0, 'night']]],
 [['boundary: diffuse fraction at threshold', [400, 280, 30, 70, 10], [0.0, 'diffuse']],
  ['boundary: blend band lower edge', [400, 240, 30, 70, 10], [30.0, 'track']],
  ['normal: clear sky', [800, 80, -45, 70, 10], [-45.0, 'track']],
  ['regression: diffuse threshold', [100, 60, 45, 60, 10], [0.0, 'diffuse']],
  ['regression: diffuse threshold (partial repair)', [100, 60, 45, 60, 20], [0.0, 'diffuse']],
  ['control 1', [100, 400, -30, 70, 0], [0.0, 'diffuse']],
  ['control 2', [100, 0, 0, 70, 0], [0.0, 'track']]],
 [['boundary: diffuse fraction at threshold', [400, 280, 30, 70, 10], [0.0, 'diffuse']],
  ['boundary: blend band lower edge', [400, 240, 30, 70, 10], [30.0, 'track']],
  ['normal: clear sky', [800, 80, -45, 70, 10], [-45.0, 'track']],
  ['regression: diffuse threshold', [100, 60, 45, 60, 20], [0.0, 'diffuse']],
  ['regression: diffuse threshold (partial repair)', [100, 80, -30, 80, 20], [0.0, 'diffuse']],
  ['control 1', [200, 160, 25, 70, 0], [0.0, 'diffuse']],
  ['control 2', [800, 160, -50, 80, 20], [-50.0, 'track']]],
 [['boundary: diffuse fraction at threshold', [400, 280, 30, 70, 10], [0.0, 'diffuse']],
  ['boundary: blend band lower edge', [400, 240, 30, 70, 10], [30.0, 'track']],
  ['normal: clear sky', [800, 80, -45, 70, 10], [-45.0, 'track']],
  ['regression: diffuse threshold', [100, 80, -30, 80, 20], [0.0, 'diffuse']],
  ['regression: diffuse threshold (partial repair)', [200, 160, 25, 80, 20], [0.0, 'diffuse']],
  ['control 1', [400, 80, -30, 80, 0], [-30.0, 'track']],
  ['control 2', [0, 60, 25, 80, 0], [0.0, 'night']]],
 [['boundary: diffuse fraction at threshold', [400, 280, 30, 70, 10], [0.0, 'diffuse']],
  ['boundary: blend band lower edge', [400, 240, 30, 70, 10], [30.0, 'track']],
  ['normal: clear sky', [800, 80, -45, 70, 10], [-45.0, 'track']],
  ['regression: diffuse threshold', [200, 160, 25, 80, 20], [0.0, 'diffuse']],
  ['regression: diffuse threshold (partial repair)', [100, 80, -50, 80, 0], [0.0, 'diffuse']],
  ['control 1', [400, 400, 0, 80, 10], [0.0, 'diffuse']],
  ['control 2', [100, 400, -30, 70, 0], [0.0, 'diffuse']]]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
boundary: diffuse fraction at threshold	`[0.0, 'diffuse']`	`[0.0, 'diffuse']`	Passed
boundary: blend band lower edge	`[30.0, 'track']`	`[30.0, 'track']`	Passed
normal: clear sky	`[-45.0, 'track']`	`[-45.0, 'track']`	Passed
regression: diffuse threshold	`[0.0, 'diffuse']`	`[0.0, 'diffuse']`	Passed
regression: diffuse threshold (partial repair)	`[0.0, 'diffuse']`	`[0.0, 'diffuse']`	Passed
control 1	`[0.0, 'diffuse']`	`[0.0, 'diffuse']`	Passed
control 2	`[0.0, 'night']`	`[0.0, 'night']`	Passed

SHA-256 / 65cd7823e28c02e62fd6872dc704b6243bdf0758555bfd16585a2cb83301cdbc

Verification & scope

Deterministic stipulated toy contract for teaching; no claim of conformance with any standard, vendor protocol or production controller. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:51:57.416852+00:00.

Case digest / 92924b020e5a65cb49c1fabbe416660fb6162bd4572b35e5b990bac16a91ef0c