Inertia tensor #55
Inertia tensor #55
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…ed_aperture_properties
kinematic_properties.py
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| # 3x3 inertia tensor | ||
| Itensor = (mass[:, None, None] * position[:, None:, None] * position[:, None]).sum( | ||
| Itensor = (mass[:, None, None]/mass.sum() * position[:, None:, None] * position[:, None]).sum( |
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Why are you changing the units of the inertia tensor (not saying you shouldn't, I'm just curious as to why)? Do you know of anyone else who uses this property that will need to be informed of the change?
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This is because of the convention of the inertia tensor in intrinsic alignment context. In general physics, people the inertia tensor as m*r^2 but in the context of intrinsic alignment, we usually divide by the total mass of the object. (see e.g. eq. 7,8 of https://arxiv.org/abs/2309.08605). I am only aware of Aniruddh currently working on IA and I already informed him.
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| return Itensor | ||
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| def get_reduced_inertia_tensor(mass, position): |
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There is quite a lot of duplicated code shared with get_inertia_tensor. Could you combine these functions by passing a keyword argument, e.g. get_inertia_tensor(mass, position, reduce=False)
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Yes, I will make the changes
| Itensor = np.concatenate([np.diag(Itensor), Itensor[np.triu_indices(3, 1)]]) | ||
| return Itensor | ||
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| def get_reduced_projected_inertia_tensor(mass, position, axis): |
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You could also pass a keyword argument to get_projected_inertia_tensor
kinematic_properties.py
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| Itensor = Itensor.sum(axis=0) | ||
| Itensor = ( | ||
| np.array((Itensor[0, 0], Itensor[1, 1], Itensor[0, 1])) |
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Do you need to multiply by units here?
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The reduced projected inertia tensor is unitless
Included reduced inertia and reduced projected inertia tensors. Changed the inertia tensor calculation by dividing by the total mass.