§85's "impossible mass/inertia values" for the inertia tensor (§23).
Every entry must be finite and the three diagonal entries — the principal
moments — must be non-negative, because a negative moment of inertia
describes no physical body and makes the angular solve diverge. Off-diagonal
products of inertia are legitimately signed and are only checked for
finiteness.
In a "2d" world only the Z diagonal entry is used (§23), so the rest is
still checked for sanity but cannot affect the simulation.
§85's "impossible mass/inertia values" for the inertia tensor (§23).
Every entry must be finite and the three diagonal entries — the principal moments — must be non-negative, because a negative moment of inertia describes no physical body and makes the angular solve diverge. Off-diagonal products of inertia are legitimately signed and are only checked for finiteness.
In a
"2d"world only the Z diagonal entry is used (§23), so the rest is still checked for sanity but cannot affect the simulation.