Research

Publications

Computational geometry, geometric probability, algorithms and discrete mathematics. Preprints are identified separately from journal and conference publications.

2026

Deficit coordinates reveal a quadrilateral for d = 3 and the face structure of a cube for d = 4. Vertex labels record cuts; matching colors and line styles track the corresponding facets or edges.
Preprint2026

Ehrhart h*-polynomials of (132,213)-avoiding permutation polytopes: A repair cone and eventual real-rootedness

Pedro M. M. de Castro

arXiv, preprint, v1

Describes the geometry of pattern-avoiding permutation polytopes and proves real-rootedness in two dimension ranges. The intermediate range remains open.

Discrete mathematics

The green spine joins successive memory positions; orange branches lead to the incoming points.
Preprint2026

Sequential Euclidean connections with exponential memory: distributional performance and adversarial robustness

Pedro M. M. de Castro

arXiv, preprint, v2

Analyzes connection costs for sequential points using an exponentially weighted moving state, comparing random-input performance with adversarial robustness.

Geometric probability

Examples of the three minimum-blocker families on ten ordered vertices. Removing any one of these five-edge sets destroys every nonnested perfect matching.
Preprint2026

Minimum blockers and extremal graphs for nonnested matchings

Pedro M. M. de Castro

arXiv, preprint, v2 · 8 October 2026 · 30 pages, 11 figures, 1 algorithm

Classifies all minimum blockers for nonnested perfect matchings and constructs ordered graphs exceeding a proposed extremal bound by a quadratic number of edges.

Discrete mathematics

In (a) and (b), the five original vertices give different named reports for the blue and orange edges. In (c), both reports become {1,1,4,4,4} when the names are removed. This ambiguity motivates a less symmetric choice of landmarks.
Preprint2026

Edge multiset dimension of subdivided complete graphs

Pedro M. M. de Castro

Zenodo, preprint, v3.0

Studies the landmarks needed to identify edges after landmark names are removed from distance reports. Gives asymptotic bounds for fixed subdivision lengths and existence results for lengths two and three.

Discrete mathematics

Why green fails in the ten-vertex counterexample: a three-edge green matching must contain {3,8}. In (a), avoiding nesting then requires a red edge. In (b), the all-green alternative contains a nested pair.
Figure 4 in the note ·
Preprint2026

Counterexamples to the multicolor nonnested matching conjecture

Pedro M. M. de Castro

Hexagon, preprint, v1 · 18 October 2026

Constructs explicit counterexamples to the conjecture of Barát, Gyárfás and Tóth with equally sized targets, for every number of colors and target size at least three. These examples show that excluding nested pairs raises the classical matching Ramsey threshold by at least one vertex.

Discrete mathematics

2019

A construction showing that going from Delaunay to Apollonius can't be done in less than Ω(n log n). 
Conference paper2019

Hardness results on Voronoi, Laguerre and Apollonius diagrams

Kevin Buchin, Pedro Machado Manhães de Castro, Olivier Devillers, Menelaos Karavelas

Proceedings of the 31st Canadian Conference on Computational Geometry (CCCG 2019), pp. 99–104

Establishes lower bounds for converting Voronoi-related diagrams and gives a randomized incremental construction for an Apollonius diagram.

Computational geometry

2018

2017

Some hard configurations for the Reachability with Direction Constraints Problem.
Conference paper2017

Reachability in a Planar Subdivision with Direction Constraints

Daniel Binham, Pedro Machado Manhães de Castro, Antoine Vigneron

33rd International Symposium on Computational Geometry (SoCG 2017); Leibniz International Proceedings in Informatics (LIPIcs) 77, pp. 17:1–17:15

Studies reachability in planar subdivisions with directional constraints, with an efficient algorithm and a hardness result for a broader variant.

Computational geometry

2016

2014

2013

2012

2011

2010

A spherical Delaunay triangulation with nonuniformly distributed points.
Conference paper2010

Robust and Efficient Delaunay Triangulations of Points on Or Close to a Sphere

Manuel Caroli, Pedro M. M. de Castro, Sébastien Loriot, Olivier Rouiller, Monique Teillaud, Camille Wormser

Experimental Algorithms (SEA 2010); Lecture Notes in Computer Science 6049, pp. 462–473

Presents robust incremental methods for Delaunay triangulations of points on or close to a sphere, implemented with CGAL.

Computational geometry

2009

2007

Circular-arc geometry in a VLSI layout, with magnified details.
Conference abstract2007

Exact and efficient computations on circles in CGAL

Pedro Machado Manhães de Castro, Sylvain Pion, Monique Teillaud

Abstracts of the 23rd European Workshop on Computational Geometry, pp. 219–222

Investigates efficient exact computations for circles and circular arcs in CGAL, with VLSI data used for evaluation.

Computational geometry

2003

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