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fix: FDyn outputs a zero qdd before its first derivative call - #935
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FDyn.qdd was None until deriv() had run once. bdsim records the type of every block output when it compiles a diagram and checks it at run time, so the first evaluation failed with 'output 2 changed signature: was NoneType, now ndarray'. Start from zeros, as the other dynamics block in this file does. Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Up to standards ✅🟢 Issues
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| Metric | Results |
|---|---|
| Complexity | 0 |
| Duplication | 0 |
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FDynheldself._qdd = Noneuntilderiv()had run once, so its third output (qdd) wasNoneon the first evaluation. bdsim records the type of each block output at compile time and checks it at run time (check=Trueby default), so a diagram containingFDynfailed on the first step:Found running the computed-torque model (
computed-torque.bd) in bdsim's ICRA 2026 tutorial notebook.Change.
qddstarts asnp.zeros(robot.n), which is what the other dynamics block inarm.pyalready does. Nothing changes oncederiv()has run; the only visible difference is the first output,Nonebefore and zeros now.Tested. New
test_fdyn_qdd_before_derivfails without the change and passes with it;tests/test_blocks.pypasses (30 passed, 6 skipped). With the fix, bdsim'sicra2026notebook runs end to end, including the computed-torque cell. Not run: the rest of the RTB suite.AI assistance: written with Claude Code (Claude Sonnet 5.5), reviewed by the maintainer. Changes a block's initial output only; no numerical results change.
🤖 Generated with Claude Code