Seemingly unrelated defaults make model compilation non-idempotent

[jjyyxx]

Intro

Hi!

I am a graduate student at HKU, I use MuJoCo for my research on robotic manipulation.

My setup

MuJoCo 3.3.0, Python and C, Linux

What's happening? What did you expect?

By having an unrelated and unused <geom density="0" /> default entry (density attribute is necessary here), the model compilation becomes non-idempotent — it throws error Error: eigenvalue of mesh inertia must be positive: a on the second invocation.

Steps for reproduction

Run snippet below.

Minimal model for reproduction

No response

Code required for reproduction

import mujoco
spec = mujoco.MjSpec.from_string("""
<mujoco>
  <default>
    <geom density="0" />
    <mesh/>
  </default>
  <asset>
    <mesh name="a" vertex="0 0 0 1 0 0 0 1 0 0 0 1" scale="10 10 10" />
  </asset>
  <worldbody/>
</mujoco>
""")
model = spec.compile()
model = spec.compile()  # Error: eigenvalue of mesh inertia must be positive: a

Confirmations

• I searched the latest documentation thoroughly before posting.
• I searched previous Issues and Discussions, I am certain this has not been raised before.

[yuvaltassa]

This indeed looks like a bug. Thanks.