Talk:Monostatic polytope
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WHO and WHEN did discover (invent?) it?[edit]
The article says in the lead:
- They [i.e., monostatic polytopes] were described in 1969 by J.H. Conway, M. Goldberg and R.K. Guy. The monostatic polytope in 3-space they constructed has 19 faces.
while Richard K. Guy in the 3rd para of Mathematics section says:
- Around 1959, Guy discovered a unistable polyhedron having only 19 faces
If Guy discovered them, why Conway & Goldberg are mentioned as co-authors of the discovery? And why did Guy wait ten years with publication? --CiaPan (talk) 22:14, 9 July 2018 (UTC)
- The 1959 seems to be a typo, it should be 1968 (see http://www.logika.si/poliedriCDsl/UnistablePolyhedron.pdf) which is consistent. Invent and describe are two separate events so it may not be the same people doing them. --RDBury (talk) 01:54, 12 July 2018 (UTC)
Accuracy of figure[edit]
Knowlton shows a "phase diagram" calculated by David Shafer for stability of the 19-sided solid as a function of lengths of the longest and shortest longitudinal edges measured in terms of a characteristic radius. The minimum longest/shortest ratio for monostability is about 32:1, and the minimum ratio of the longest edge to the radius is about 14:1. Assuming this diagram is correct, the Wikipedia illustration is at best impressionistic. Mdmi (talk) 20:53, 1 July 2022 (UTC)
- @Mdmi I copied the coordinates directly from the paper. I can't guarantee I didn't make a mistake, though. I've lost the original GeoGebra file so I can't check. 187.138.86.183 (talk) 06:03, 2 July 2022 (UTC)
- The paper mentions two constraints on solution parameters a and b: The center of gravity must lie below O and above P in Figure 6. A formula is given for the first constraint, but not for the second.
- The x-coordinate, c, of the center of gravity satisfies cV = M, where M is the moment about O and V is the volume. The paper calculates the moment in terms of integrals in which the integrand is xyz dx. The volume would be given by the same formula with the integrands replaced by yz dx. For comparison with c, the x coordinate of P can be deduced from figure 6.
- Do you remember having to work out the volume integral or center of gravity, neither of which can be copied from the paper? If not, coordinates calculated for a particular choice of a and b would be suspect for not having been checked against the second constraint. Mdmi (talk) 10:14, 5 July 2022 (UTC)