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BUG: Fix incorrect Jacobian in only_radial_burn branch of SolidMotor.evaluate_geometry #944

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Merged
MateusStano merged 3 commits into from
Mar 20, 2026
+8 −5
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BUG: Fix incorrect Jacobian in only_radial_burn branch of SolidMotor.evaluate_geometry #944

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Initial plan
Copilot Mar 20, 2026
60924a5
BUG: Fix incorrect Jacobian in only_radial_burn branch of evaluate_ge…
Copilot Mar 20, 2026
4ad0554
Merge branch 'rel/v1.12.0' into copilot/sub-pr-935
MateusStano Mar 20, 2026
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2 changes: 2 additions & 0 deletions CHANGELOG.md
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Expand Up @@ -80,6 +80,8 @@ Attention: The newest changes should be on top -->
- BUG: Fix parallel Monte Carlo simulation showing incorrect iteration count [#806](https://github.com/RocketPy-Team/RocketPy/pull/806)
- BUG: Fix missing titles in roll parameter plots for fin sets [#934](https://github.com/RocketPy-Team/RocketPy/pull/934)
- BUG: Duplicate _controllers in Flight.TimeNodes.merge() [#931](https://github.com/RocketPy-Team/RocketPy/pull/931)
- BUG: Fix incorrect Jacobian in `only_radial_burn` branch of `SolidMotor.evaluate_geometry` [#935](https://github.com/RocketPy-Team/RocketPy/pull/935)
- BUG: Add explicit timeouts to ThrustCurve API requests [#935](https://github.com/RocketPy-Team/RocketPy/pull/935)

## [v1.11.0] - 2025-11-01

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11 changes: 6 additions & 5 deletions rocketpy/motors/solid_motor.py
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Expand Up @@ -546,13 +546,14 @@ def geometry_jacobian(t, y):
2 * np.pi * (grain_inner_radius * grain_height) ** 2
)

inner_radius_derivative_wrt_inner_radius = factor * (
grain_height - 2 * grain_inner_radius
)
inner_radius_derivative_wrt_height = 0
# burn_area = 2π*r*h, so ṙ = -vdiff/(2π*r*h):
# ∂ṙ/∂r = vdiff/(2π*r²*h) = factor * h
# ∂ṙ/∂h = vdiff/(2π*r*h²) = factor * r
inner_radius_derivative_wrt_inner_radius = factor * grain_height
inner_radius_derivative_wrt_height = factor * grain_inner_radius
# dh/dt = 0, so all partial derivatives of height are zero
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@Gui-FernandesBR Gui-FernandesBR Mar 20, 2026

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Suggested change
# dh/dt = 0, so all partial derivatives of height are zero
# dh/dt = 0 (Height is a constant), so all partial derivatives of height are zero

height_derivative_wrt_inner_radius = 0
height_derivative_wrt_height = 0
# Height is a constant, so all the derivatives with respect to it are set to zero

return [
[
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