Fix island discovery with multiple coupled trees#3088
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Ashutosh0x wants to merge 1 commit intogoogle-deepmind:mainfrom
Open
Fix island discovery with multiple coupled trees#3088Ashutosh0x wants to merge 1 commit intogoogle-deepmind:mainfrom
Ashutosh0x wants to merge 1 commit intogoogle-deepmind:mainfrom
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When a constraint row involves multiple trees (e.g., in a complex tendon equality), the number of edges added to the adjacency graph can exceed the number of non-zeros in the Jacobian row. This change increases the size of the temporary edge array to 2*nJ edges (4*nJ integers), ensuring sufficient space for graph construction. Fixes google-deepmind#3073
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This Pull Request fixes a crash in the MuJoCo engine when loading models with equality constraints that couple many bodies (e.g., complex tendon equalities).
The Problem
During island discovery, the engine builds an adjacency graph of bodies (trees). The temporary edge array was sized to hold at most
J (number of non-zeros in the constraint Jacobian) edges. However, when a single constraint row involves $ distinct trees, it can contribute up to (k-1)$ edges to the graph. If (k-1) > k$, the edge array can be too small even if \le nJ$.
The Fix
Increased the size of the temporary edge array from
J edges to 2nJ edges (and 4nJ integers). This provides a safe upper bound for any configuration of constraints.
Fixes #3073