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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 …
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 …
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 …
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 …
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 …
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 …
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 …
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 …
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 …
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 …
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 …
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 …
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 $5\times 12$ …
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 …
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 $n$.