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Natalia García-Colín

Publications and source records attributed to Natalia García-Colín.

7 recordsLinked to original sources
arXiv2024

A note on girth-diameter cages

In this paper, we introduce a problem closely related to the Cage Problem and the Degree Diameter Problem. For integers $k\geq 2$, $g\geq 3$ and $d\geq 1$, we define a $(k;\, g,d)$-graph to be a $k$-regular graph with girth $g$ and diameter $d$. We denote by $n_0(k;\,g,d)$ the smallest possible order of such a graph, and, if such a graph exists, we call it a $(k;g,d)$-cage. In particular, we focus on $(k;\,5,4)$-graphs. We show that $n_0(k;\,5,4) \geq k^2+k+2$ for all $k$, and report on the determination of all $(k;\,5,4)$-cages for $k=3, 4$ and $5$ and examples with $k = 6$, and describe some examples of $(k;\,5,4)$-graphs which prove that $n_0(k;\,5,4) \leq 2k^2$ for infinitely many values of $k$.

math.CO↗
arXiv2023

There is no perfect Mondrian partition for squares of side lengths less than 1001

In mathematics, a dissection of a square (or rectangle) into non-congruent rectangles is a Mondrian partition. If all the rectangles have the same area, it is called a perfect Mondrian partition. In this paper, we present a computational result by which we can affirm that there is no perfect Mondrian partition of a length $n$ square for $n\leq 1000$. Using the same algorithm we have been able to establish that there is no perfect Mondrian partition of a $n \times m$ rectangle for $n,m \leq 400$.

math.CO↗
arXiv2021

On the number of vertices of projective polytopes

Let $X$ be a configuration of $n$ points in $\mathbb{R}^d$. What is the maximum number of vertices that $conv(T(X))$ can have among all the possible permissible projective transformations $T$? In this paper, we investigate this and connected questions. After presenting several upper bounds, we study a closely related problem (via Gale transforms) concerning the number of minimal Radon partitions of a set of points. We then present some bounds for this number that enable us to partially answer a question due to Pach and Szegedy. We also discuss another related problem concerning the size of topes in arrangements of hyperplanes.

math.CO↗
arXiv2019

Scaffold for the polyhedral embedding of cubic graphs

Let $G$ be a cubic graph and $Π$ be a polyhedral embedding of this graph. The extended graph, $G^{e},$ of $Π$ is the graph whose set of vertices is $V(G^{e})=V(G)$ and whose set of edges $E(G^{e})$ is equal to $E(G) \cup \mathcal{S}$, where $\mathcal{S}$ is constructed as follows: given two vertices $t_0$ and $t_3$ in $V(G^{e})$ we say $[t_0 t_3] \in \mathcal{S},$ if there is a $3$--path, $(t_0 t_1 t_2 t_3) \in G$ that is a $Π$-- facial subwalk of the embedding. We prove that there is a one to one correspondence between the set of possible extended graphs of $G$ and polyhedral embeddings of $G$.

math.CO↗
arXiv2018

Regular and biregular planar cages

We study the Cage Problem for regular and biregular planar graphs. A $(k,g)$-graph is a $k$-regular graph with girth $g$. A $(k,g)$-cage is a $(k,g)$-graph of minimum order. It is not difficult to conclude that the regular planar cages are the Platonic Solids. A $(\{r,m\};g)$-graph is a graph of girth $g$ whose vertices have degrees $r$ and $m.$ A $(\{r,m\};g)$-cage is a $(\{r,m\};g)$-graph of minimum order. In this case we determine the triplets of values $(\{r,m\};g)$ for which there exist planar $(\{r,m\};g)$--graphs, for all those values we construct examples. Furthermore, for many triplets $(\{r,m\};g)$ we build the $(\{r,m\};g)$-cages.

math.CO↗
arXiv2016

A note on the tolerated Tverberg theorem

In this paper we give an asymptotically tight bound for the tolerated Tverberg Theorem when the dimension and the size of the partition are fixed. To achieve this we study certain partitions of order-type homogeneous sets and use a generalization of the Erdős-Szekeres theorem.

math.CO↗