Principle:Google deepmind Mujoco MJX Data Retrieval
| Knowledge Sources | |
|---|---|
| Domains | GPU_Computing, Physics_Simulation, JAX |
| Last Updated | 2026-02-15 06:00 GMT |
Overview
Mechanism for transferring simulation results from a JAX device back to CPU as standard MuJoCo data structures.
Description
MJX Data Retrieval converts GPU-resident mjx.Data back into CPU-resident mujoco.MjData objects. This is needed for visualization (the MuJoCo renderer uses CPU data), logging, analysis, or interfacing with non-JAX code. Two variants are provided: get_data_into writes into a pre-allocated MjData (zero-allocation), while get_data allocates new MjData objects. Both handle batched data by returning lists.
Usage
Use when visualization or CPU-side processing is needed. For RL training, retrieval is typically done only for rendering or checkpointing, not every step.
Theoretical Basis
Retrieval involves:
- Device-to-host transfer: jax.device_get copies arrays from GPU to CPU
- Field mapping: JAX arrays are written back to corresponding MjData fields
- Batch handling: For batched data, results are split into individual MjData objects
- Contact reconstruction: Contact data is unpacked from the flat MJX representation
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