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Finite or discrete collections of geometric objects. Packings, tilings, polyhedra, polytopes, intersection, arrangements, rigidity.

2 votes
Accepted

Partitioning convex polygons into quadrilaterals of equal area and perimeter

Convex quadrilateral decompositions of equal area are always possible. Given a convex polygon $P$ with at least $5$ sides, draw a line from one of the vertices of $P$ to a point $Q$ on one of the edge …
RavenclawPrefect's user avatar
7 votes

Intersecting cylinders around a sphere

Not a proof, but some thoughts on how to get empirical data for this problem and evidence for the optimal configuration: Suppose we have a matrix $C$ whose rows are the unit vectors pointing in the di …
RavenclawPrefect's user avatar
5 votes

Solution to Erdos-Ulam problem

The error is in this sentence: As a circle with its centre on the Base Plane, $T_{n-1}$ will have at least two points on the Base Plane. Circles in an ambient space of more than three dimensions don …
RavenclawPrefect's user avatar
5 votes
Accepted

Family of shapes that can be tiled into one another

Any member of a nontrivial family like this has to be a rep-tile; looking among those will give you many examples. Some specific examples: The family of all rectifiable polyominoes, which includes al …
RavenclawPrefect's user avatar
5 votes
0 answers
77 views

What tools can show that (possibly irregular) dodecahedra do not fill space?

(Formerly on MSE.) Here is a fairly natural question: Can three-dimensional space be filled with convex polyhedra of the same incidence structure (if not the same geometry) as the regular dodecahedron …
RavenclawPrefect's user avatar
1 vote

Cutting convex regions into equal diameter and equal least width pieces

This is not a complete answer to all 6 questions, but provides some progress: 1. I assume that you want $C$ to be bounded here? Your language throughout the post seems to assume it. If not, then eithe …
RavenclawPrefect's user avatar
5 votes

Which convex pentagon gives least packing density?

The answer is (very likely) no for all $n>20$. Let $R_n$ be the regular $n$-gon of circumradius $1$, and given a convex shape $C$, let $\delta(C)$ be its maximal packing density in the plane. Observe …
RavenclawPrefect's user avatar
5 votes

Tiling planar integer lattice by finite point sets

Every such $S$ has a periodic tiling, in which finitely many disjoint copies form a set with one representative for each translate of some discrete lattice $L$ - see Bhattacharya 2016 or Greenfeld and …
RavenclawPrefect's user avatar
2 votes

On largest convex m-gons contained in a given convex n-gon where m < n

The maximum area inscribed convex $m$-gon can always be found on the vertices. To do this, just consider moving one vertex at a time; we gain area the further we move this point from the diagonal conn …
RavenclawPrefect's user avatar
7 votes
Accepted

Are there any convex pentagonal rep-tiles?

Question 2 can be answered in the affirmative, at least: there are many triangles with the multi-way rep-tile property. Every triangle has a simple tiling of itself with $k^2$ copies (just take the af …
RavenclawPrefect's user avatar
3 votes

On packing axisymmetric bodies in 3D

As a supplementary answer, here are some notes on the 2D analog mentioned in the original post. The conjecture is false for nonconvex bodies: The above shape can tile the plane without gaps when rota …
RavenclawPrefect's user avatar
8 votes

Finite set of non-collinear points on plane with every point having ≥ 3 equidistant neighbors?

Yes. Place five points $P_1,P_2,P_3,P_4,P_5$ in a regular pentagon inscribed in the unit circle centered at the origin. For each of these points $P$, we're going to add another point $Q$ somewhere on …
RavenclawPrefect's user avatar
12 votes

Tiling the plane with pairwise non-congruent rational triangles

Yes, it is possible; in fact, we can do it entirely with $5-12-13$ right triangles at different scales. First, note that we can three triangles at scales in the ratio $5:12:13$ to form a $5\times 12$ …
RavenclawPrefect's user avatar
2 votes
Accepted

To find the convex planar region minimizing diameter when area and perimeter are given

The 2000 paper Inequalities for Convex Sets, by Paul R. Scott and Poh Way Awyong, lists various inequalities on 2D convex bodies as described here; for your question you can see the state of the resea …
RavenclawPrefect's user avatar
3 votes

On cutting tetrahedrons into mutually congruent pieces

This MSE question exhibits two non-regular tetrahedra which can be decomposed into 8 smaller copies congruent to themselves; this yields $8^n$ for any $n$.
RavenclawPrefect's user avatar

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