{"abstract":"Reduce-scatter gives every rank the first slice.","category":"Distributed training aggregation","checks":6,"contract":"Sum equal-length worker vectors, then return width values beginning at rank*width; invalid/empty slices return [].","contract_signature":"parts, rank, width","evaluation_group":"w3-dta-reduce-scatter-slice","failed_approach":"Offsetting by rank while returning too short a slice truncates later ownership blocks.","family":"w3-distributed-training-aggregation-reduce-scatter-slice","id":"FA-99301","implementations":{"attempt":{"sha256":"727af68e7734a81880eb734f371f3e4c7252f76611564c07d8230c768a34d11d","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(parts, rank, width):\n    s=[sum(v[j] for v in parts) for j in range(len(parts[0]))] if parts else []; return s[rank:rank+width]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\np=[[N,2,3,4],[10,20,30,40]]\ncheck('rank one',solve(p,1,2),[33,44])\ncheck('rank zero',solve(p,0,2),[N+10,22])\ncheck('last short',solve(p,1,3),[44])\ncheck('empty input',solve([],0,2),[])\ncheck('zero width',solve(p,1,0),[])\ncheck('singleton block',solve([[N,2]],0,1),[N])\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":"22cf32792ed557715f2ff70b468ea503bc3ddae4c073827786a32a8d7adf79c3","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(parts, rank, width):\n    s=[sum(v[j] for v in parts) for j in range(len(parts[0]))] if parts else []; return s[:width]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\np=[[N,2,3,4],[10,20,30,40]]\ncheck('rank one',solve(p,1,2),[33,44])\ncheck('rank zero',solve(p,0,2),[N+10,22])\ncheck('last short',solve(p,1,3),[44])\ncheck('empty input',solve([],0,2),[])\ncheck('zero width',solve(p,1,0),[])\ncheck('singleton block',solve([[N,2]],0,1),[N])\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":"Inputs are already materialized Python values from a fixed toy collective; no transport, failure recovery, optimizer state, or real model behavior is represented. 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":"w3-distributed-training-aggregation-reduce-scatter-slice","generated_at":"2026-09-30T16:48:22.633689+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"A toy distributed-training contract makes replica and shard contribution rules explicit without claiming framework compatibility or performance.","root_cause":"After summing gradients, each rank should own its indexed equal-width segment.","sha256":"ae49bfba080a0af8c8413ac1f7e62a9c26bf8161ad49a783c5647ad2d4643e1d","title":"Reduce-scatter gives every rank the first slice · case 01","variant":1,"variant_policy":"The fixture code references N, supplied as 1 through 5. Fixed boundary checks may repeat. These records share one mechanism and must remain together in evaluation splits.","verified":true,"visibility":"public","verification":{"attempt":{"elapsed_ms":28.242,"exit_code":1,"observations":[{"actual":[22,33],"check":"rank one","expected":[33,44],"passed":false},{"actual":[11,22],"check":"rank zero","expected":[11,22],"passed":true},{"actual":[22,33,44],"check":"last short","expected":[44],"passed":false},{"actual":[],"check":"empty input","expected":[],"passed":true},{"actual":[],"check":"zero width","expected":[],"passed":true},{"actual":[1],"check":"singleton block","expected":[1],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"rank one\", \"actual\": [22, 33], \"expected\": [33, 44], \"passed\": false}, {\"check\": \"rank zero\", \"actual\": [11, 22], \"expected\": [11, 22], \"passed\": true}, {\"check\": \"last short\", \"actual\": [22, 33, 44], \"expected\": [44], \"passed\": false}, {\"check\": \"empty input\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"zero width\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"singleton block\", \"actual\": [1], \"expected\": [1], \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":27.301,"exit_code":1,"observations":[{"actual":[11,22],"check":"rank one","expected":[33,44],"passed":false},{"actual":[11,22],"check":"rank zero","expected":[11,22],"passed":true},{"actual":[11,22,33],"check":"last short","expected":[44],"passed":false},{"actual":[],"check":"empty input","expected":[],"passed":true},{"actual":[],"check":"zero width","expected":[],"passed":true},{"actual":[1],"check":"singleton block","expected":[1],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"rank one\", \"actual\": [11, 22], \"expected\": [33, 44], \"passed\": false}, {\"check\": \"rank zero\", \"actual\": [11, 22], \"expected\": [11, 22], \"passed\": true}, {\"check\": \"last short\", \"actual\": [11, 22, 33], \"expected\": [44], \"passed\": false}, {\"check\": \"empty input\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"zero width\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"singleton block\", \"actual\": [1], \"expected\": [1], \"passed\": true}], \"passed\": false}\n"}},"member_only":{"stages":["fixed"],"fields":["implementations.fixed","verification.fixed","harness","repair"],"note":"The verified repair, its recorded checks, the repair description, and the scoring harness are available to members."}}