{"abstract":"SIP distortion is evaluated after the linear WCS transform.","category":"Astronomical coordinate conventions","checks":6,"contract":"Reduced SIP model for reference-relative pixel offsets u,v: corrected pair (u+a*u*u+b*u*v,v), followed by diagonal linear matrix (sx,sy). Return intermediate coordinates, no sky projection or full SIP implementation.","evaluation_group":"model-56119d6820d9ef3c","failed_approach":"Moving only the square term before the matrix leaves the mixed term in the wrong basis.","family":"z-astronomy-sip-before-linear","id":"FA-12181","implementations":{"attempt":{"sha256":"9d885096e1f3b9338b125316a6e6d67e846053617dc15e7c94bb41d990f4b28d","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(u, v, a, b, sx, sy):\n    return [sx*(u+a*u*u)+b*(sx*u)*(sy*v),sy*v]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('square and cross distortion', solve(N,2,1,1,3,4), [3*(N+N*N+2*N),8])\ncheck('cross term only', solve(N,2,0,1,3,4), [9*N,8])\ncheck('square only', solve(N,0,1,0,3,4), [3*(N+N*N),0])\ncheck('reference origin', solve(0,0,1,1,3,4), [0,0])\ncheck('identity transform', solve(N,2,1,1,1,1), [N+N*N+2*N,2])\ncheck('no distortion', solve(N,-2,0,0,3,4), [3*N,-8])\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"},"broken":{"sha256":"a0736d8663079cee35c466074501ecd4c8f7874c59784d50e6aed3520fc84570","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(u, v, a, b, sx, sy):\n    return [sx*u+a*(sx*u)**2+b*(sx*u)*(sy*v),sy*v]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('square and cross distortion', solve(N,2,1,1,3,4), [3*(N+N*N+2*N),8])\ncheck('cross term only', solve(N,2,0,1,3,4), [9*N,8])\ncheck('square only', solve(N,0,1,0,3,4), [3*(N+N*N),0])\ncheck('reference origin', solve(0,0,1,1,3,4), [0,0])\ncheck('identity transform', solve(N,2,1,1,1,1), [N+N*N+2*N,2])\ncheck('no distortion', solve(N,-2,0,0,3,4), [3*N,-8])\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"},"fixed":{"sha256":"0d9eac558fd64ba6851da847f12b4a69172e561f464af2df741a31851e02a797","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(u, v, a, b, sx, sy):\n    return [sx*(u+a*u*u+b*u*v),sy*v]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('square and cross distortion', solve(N,2,1,1,3,4), [3*(N+N*N+2*N),8])\ncheck('cross term only', solve(N,2,0,1,3,4), [9*N,8])\ncheck('square only', solve(N,0,1,0,3,4), [3*(N+N*N),0])\ncheck('reference origin', solve(0,0,1,1,3,4), [0,0])\ncheck('identity transform', solve(N,2,1,1,1,1), [N+N*N+2*N,2])\ncheck('no distortion', solve(N,-2,0,0,3,4), [3*N,-8])\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"}},"limitations":"Reduced deterministic algebraic model only; no ephemeris, full sky projection, or physical accuracy claims. 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.","method":"Deterministic executable model with adversarial boundary fixtures.","provenance":{"created_by":"Failure Map","dependencies":"Python standard library","family":"z-astronomy-sip-before-linear","generated_at":"2026-09-29T14:38:54.579426+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"Astronomical coordinate adapters must preserve convention semantics. Primary background: https://docs.astropy.org/en/stable/api/astropy.wcs.WCS.html","repair":"Evaluate the stipulated SIP polynomial in pixel offsets before applying the linear matrix.","root_cause":"Pixel-space distortion coefficients are evaluated in intermediate world coordinates.","sha256":"7d0692112b37736a3674861465775ba1b9c484dc34b15565bb7dbb27ca0202c1","title":"SIP distortion is evaluated after the linear WCS transform · case 01","variant":1,"variant_policy":"Five numbered records share a model and may reuse boundary fixtures.","verification":{"attempt":{"elapsed_ms":41.01,"exit_code":1,"observations":[{"actual":[30,8],"check":"square and cross distortion","expected":[12,8],"passed":false},{"actual":[27,8],"check":"cross term only","expected":[9,8],"passed":false},{"actual":[6,0],"check":"square only","expected":[6,0],"passed":true},{"actual":[0,0],"check":"reference origin","expected":[0,0],"passed":true},{"actual":[4,2],"check":"identity transform","expected":[4,2],"passed":true},{"actual":[3,-8],"check":"no distortion","expected":[3,-8],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"square and cross distortion\", \"actual\": [30, 8], \"expected\": [12, 8], \"passed\": false}, {\"check\": \"cross term only\", \"actual\": [27, 8], \"expected\": [9, 8], \"passed\": false}, {\"check\": \"square only\", \"actual\": [6, 0], \"expected\": [6, 0], \"passed\": true}, {\"check\": \"reference origin\", \"actual\": [0, 0], \"expected\": [0, 0], \"passed\": true}, {\"check\": \"identity transform\", \"actual\": [4, 2], \"expected\": [4, 2], \"passed\": true}, {\"check\": \"no distortion\", \"actual\": [3, -8], \"expected\": [3, -8], \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":40.487,"exit_code":1,"observations":[{"actual":[36,8],"check":"square and cross distortion","expected":[12,8],"passed":false},{"actual":[27,8],"check":"cross term only","expected":[9,8],"passed":false},{"actual":[12,0],"check":"square only","expected":[6,0],"passed":false},{"actual":[0,0],"check":"reference origin","expected":[0,0],"passed":true},{"actual":[4,2],"check":"identity transform","expected":[4,2],"passed":true},{"actual":[3,-8],"check":"no distortion","expected":[3,-8],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"square and cross distortion\", \"actual\": [36, 8], \"expected\": [12, 8], \"passed\": false}, {\"check\": \"cross term only\", \"actual\": [27, 8], \"expected\": [9, 8], \"passed\": false}, {\"check\": \"square only\", \"actual\": [12, 0], \"expected\": [6, 0], \"passed\": false}, {\"check\": \"reference origin\", \"actual\": [0, 0], \"expected\": [0, 0], \"passed\": true}, {\"check\": \"identity transform\", \"actual\": [4, 2], \"expected\": [4, 2], \"passed\": true}, {\"check\": \"no distortion\", \"actual\": [3, -8], \"expected\": [3, -8], \"passed\": true}], \"passed\": false}\n"},"fixed":{"elapsed_ms":40.599,"exit_code":0,"observations":[{"actual":[12,8],"check":"square and cross distortion","expected":[12,8],"passed":true},{"actual":[9,8],"check":"cross term only","expected":[9,8],"passed":true},{"actual":[6,0],"check":"square only","expected":[6,0],"passed":true},{"actual":[0,0],"check":"reference origin","expected":[0,0],"passed":true},{"actual":[4,2],"check":"identity transform","expected":[4,2],"passed":true},{"actual":[3,-8],"check":"no distortion","expected":[3,-8],"passed":true}],"passed":true,"stderr":"","stdout":"{\"observations\": [{\"check\": \"square and cross distortion\", \"actual\": [12, 8], \"expected\": [12, 8], \"passed\": true}, {\"check\": \"cross term only\", \"actual\": [9, 8], \"expected\": [9, 8], \"passed\": true}, {\"check\": \"square only\", \"actual\": [6, 0], \"expected\": [6, 0], \"passed\": true}, {\"check\": \"reference origin\", \"actual\": [0, 0], \"expected\": [0, 0], \"passed\": true}, {\"check\": \"identity transform\", \"actual\": [4, 2], \"expected\": [4, 2], \"passed\": true}, {\"check\": \"no distortion\", \"actual\": [3, -8], \"expected\": [3, -8], \"passed\": true}], \"passed\": true}\n"}},"verified":true,"visibility":"public"}