Update variable names in ode.system_acceleration

Co-authored-by: Alessandro Croci <[email protected]>

src/jaxsim/api/ode.py

@@ -270,15 +270,15 @@ def system_acceleration(
     )
 
     # - Joint accelerations: s̈ ∈ ℝⁿ
-    # - Base acceleration: W_v̇_WB = (W_p̈_B, W_ω̇_B) ∈ ℝ⁶
-    W_v̇_WB, s̈ = js.model.forward_dynamics_aba(
+    # - Base acceleration: O_v̇_WB = (O_p̈_B, O_ω̇_B) ∈ ℝ⁶
+    O_v̇_WB, s̈ = js.model.forward_dynamics_aba(
         model=model,
         data=data,
         joint_forces=references.joint_force_references(model=model),
         link_forces=references.link_forces(model=model, data=data),
     )
 
-    return W_v̇_WB, s̈
+    return O_v̇_WB, s̈
 
 
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