Previous Work

Here is some of my work at IME and IMPA. I've done research in different areas, such as Natural Language Processing, Algorithms, Optimization and Computer Graphics.

Extraction of noun phrases in Portuguese

We presents a set of rules for extracting noun phrases from Portuguese texts. We describe how this set was gradually obtained, starting from a machine learned set of transformation rules that was manually reviewed. The noun phrases extracted by these transformations were given as input to another learner that synthesized rules for breaking up complex noun phrases into simple ones. The results of these processes applied to a Brazilian Portuguese corpus are evaluated.

OLIVEIRA, C., FREITAS, M.C., QUENTAL, V., DOS SANTOS, C., PAES LEME, R., SOUZA, L, A Set of NP-Extraction Rules for Portuguese: Defining, Learning and Pruning, Computational Processing of the Portuguese Language, 7th International Workshop, PROPOR 2006. LNAI 3960, Springer, Berlin, 2006

Semantic Patterns in Texts

I implementated a generic stack automata to extract semantic relations from texts using certain linguistic patterns ( developed by Maria Claudia Freitas ), as well as a language to specify these patterns. These semantic relations are used to build a machine-generated ontology.

Edge-search Number in Graphs with many Symmetries

We give an algorithm for the Edge-Search Number problem. It consists on finding the minimum number of searchers to capture a fugitive that moves along the edges of a graph G. It is known to be NP-Complete. The algorithm is based on a Dijkstra search through a state space. We propose pruning the search using information from the graph's group of automorphisms.

PAULINO, R., PAES LEME, R., SIQUEIRA, T., JUSTEL, C., Edge-search-number in graphs with many automorphisms [ in Portuguese ], SBPO 2007, XXXIX SBPO, 2007, Fortaleza. Anais do XXXIX Simposio Brasileiro de Pesquisa Operacional, 2007.

Solutions of the Thomson Problem using Augmented Lagrangian Methods

We find solutions to the Thomson Problem using Augmented Lagrangian Methods. We analyse quality ( convergence to local and global minima ) and convergence rate with different initial sets of solutions and also with different formulations for the cost function and the constraints. We use the TANGO implementation of the Augmented Lagrangian.

Final Project from the course Computational Methods in Optimizations [ in Portuguese ]

Medial Axis Reconstruction

(T. Pereira and R. Paes Leme)
The Medial Axis of a shape is composed by the points whose distance to the shape is realized by more than one point in the shape. There are known methods to calculate the medial axis of polygons, polynomial curves and some other special shapes. One very important problem in the Field of 3D Reconstruction is to estimate the medial axis of a shape represented by a point cloud. It is known that the medial axis is a subset of the Voronoi diagram. A classic approach is to calculate the diagram and to filter the Voronoi facets. This approach is not robust in face of noise and outliers. In this work, we counter this problems by calculating the medial axis through random sampling of the point cloud.
[ Project Site ]

Completing Missing Regions using Symmetries

(T. Pereira and R. Paes Leme)
Symmetries are a very important aspect of many natural and human-made objects. They are common in many fields like arts, architecture, mathematics and design. A shape is symmetric if there is a transformation that maps the shape onto itself. In this work, we restrict our attention to reflective symmetries. Most symmetries that are found are not perfect. Also, some symmetries only hold in a subset of the object. These are called partial symmetries. This motivates research for algorithms that identify partial and approximate symmetries. We have implemented a symmetry detection scheme largely based on the work of Mitra et al. We develop an application of symmetry detection: completion of missing regions in objects. [ Project Site ]