# Nancy HitschfeldUniversity of Chile · Departamento de Ciencias de la Computación

Nancy Hitschfeld

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113

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Introduction

**Skills and Expertise**

## Publications

Publications (113)

In a quadtree mesh, the refinement level of a quadrant is the number of times it has been recursively split into 4 new quadrants. During the refinement process of a quadtree mesh, it is possible to lose the balance of the mesh, meaning that difference between refinement levels of two neighbor quadrants is greater than one. The balance is necessary...

Topological Data Analysis (TDA) is an emerging field that aims to discover a dataset’s underlying topological information. TDA tools have been commonly used to create filters and topological descriptors to improve Machine Learning (ML) methods. This paper proposes a different TDA pipeline to classify balanced and imbalanced multi-class datasets wit...

The Convex Hull algorithm is one of the most important algorithms in computational geometry, with many applications such as in computer graphics, robotics, and data mining. Despite the advances in the new algorithms in this area, it is often needed to improve the performance to solve more significant problems quickly or in real-time processing. Thi...

We propose a combined nodal integration and virtual element method for compressible and nearly incompressible elasticity, wherein the strain is averaged at the nodes from the strain of surrounding virtual elements. For the strain averaging procedure, a nodal averaging operator is constructed using a generalization to virtual elements of the node‐ba...

This work proposes a new GPU thread map for standard $m$-simplex domains, that scales its speedup with dimension and is energy efficient compared to other state of the art approaches. The main contributions of this work are the formulation of the new block-space map $\mathcal{H}: \mathbb{Z}^m \mapsto \mathbb{Z}^m$ which is analyzed in terms of reso...

This paper presents an algorithm to generate a new kind of polygonal mesh obtained from triangulations. Each polygon is built from a terminal-edge region surrounded by edges that are not the longest-edge of any of the two triangles that share them. The algorithm is termed Polylla and is divided into three phases. The first phase consists of labelin...

In this article, we analyze how to measure quality on meshes composed of different types of 3D linear element. In particular, we focus on meshes composed of tetrahedra, pyramids, prisms and hexahedra. We propose a metric based on the scaled Jacobian that can be applied to all four element types and it is normalized in the range [− 1,1]. We validate...

This work presents Squeeze, an efficient compact fractal processing scheme for tensor core GPUs. By combining discrete-space transformations between compact and expanded forms, one can do data-parallel computation on a fractal with neighborhood access without needing to expand the fractal in memory. The space transformations are formulated as two G...

This paper presents a GPU parallel algorithm to generate a new kind of polygonal meshes obtained from Delaunay triangulations. To generate the polygonal mesh, the algorithm first uses a classification system to label each edge of an input triangulation; second it builds polygons (simple or not) from terminal-edge regions using the label system, and...

This paper presents an algorithm to generate a new kind of polygonal mesh obtained from triangulations. Each polygon is built from a terminal-edge region surrounded by edges that are not the longest-edge of any of the two triangles that share them. The algorithm is termed Polylla and is divided into three phases. The first phase consists of labelin...

This work presents Squeeze, an efficient compact fractal processing scheme for tensor core GPUs. By combining discrete-space transformations between compact and expanded forms, one can do data-parallel computation on a fractal with neighborhood access without needing to expand the fractal in memory. The space transformations are formulated as two G...

The purpose of this work is to highlight the impact of input parameters uncertainty in discrete fracture network (DFN) models and their engineering applications. We show how the error of an input parameter, here the volumetric discontinuity intensity P32, impacts the DFN model and two important rock mechanics engineering applications: the in-situ f...

This work proposes a new approach for mapping GPU threads onto a family of discrete embedded 2D fractals. A block-space map λ:ZE2↦ZF2 is proposed, from Euclidean parallel space E to embedded fractal space F, that maps in O(log2log2(n)) time and uses no more than O(nH) threads with H being the Hausdorff dimension of the fractal, making it parallel s...

In this work, we propose new packing algorithm designed for the generation of polygon meshes to be used for modeling of rock and porous media based on the virtual element method. The packing problem to be solved corresponds to a two-dimensional packing of convex-shape polygons and is based on the locus operation used for the advancing front approac...

This work proposes a new approach for mapping GPU threads onto a family of discrete embedded 2D fractals. A block-space map $\lambda: \mathbb{Z}_{\mathbb{E}}^{2} \mapsto \mathbb{Z}_{\mathbb{F}}^{2}$ is proposed, from Euclidean parallel space $\mathbb{E}$ to embedded fractal space $\mathbb{F}$, that maps in $\mathcal{O}(\log_2 \log_2(n))$ time and u...

In this paper, we present a novel nodal integration scheme for meshfree Galerkin methods that draws on the mathematical framework of the virtual element method. We adopt linear maximum-entropy basis functions for the discretization of field variables, although the proposed scheme is applicable to any linear meshfree approximant. In our approach, th...

This paper summarizes the development of Veamy, an object-oriented C++ library for the virtual element method (VEM) on general polygonal meshes, whose modular design is focused on its extensibility. The linear elastostatic and Poisson problems in two dimensions have been chosen as the starting stage for the development of this library. The theory o...

In this paper, we present a novel nodal integration scheme for meshfree Galerkin methods that draws on the mathematical framework of the virtual element method. We adopt linear maximum-entropy basis functions for the discretization of field variables, although the proposed scheme is applicable to any linear meshfree approximant. In our approach, th...

This work presents an optimization technique that reduces the computational cost for building the Convex Hull from a set of points. The proposed method pre-processes the input set, filtering all points inside an eight-vertex polygon in O(n) time and returns a reduced set of candidate points, ordered and distributed across four priority queues. Expe...

We identify 1901 galaxy clusters (N g ≥ 2) with the VoML+G algorithm (Paper I) on the Two-Degree Field Galaxy Redshift Survey. We present the 341 clusters with at least 10 galaxies that are within 0.009 < z < 0.14 (the Catalog), of which 254 (~75%) have counterparts in the literature (NED), with the remainder (87) plausibly "new" because of incompl...

2D non-uniform polygonal meshes allow representation of the impact of landscape elements and small infrastructures on water flows. The initial vectorial mesh, derived from the intersection of several geographical information systems f layers, can have highly non-convex or sliver polygons. These bad-shaped elements compromise accurate numerical flow...

This work presents and studies the efficiency problem of mapping GPU threads onto simplex domains. A non-linear map
$\lambda (\omega)$
is formulated based on a block-space enumeration principle that reduces the number of thread-blocks by a factor of approximately
$2\times$
and
$6\times$
for 2-simplex and 3-simplex domains, respectively, when com...

Many fields of study, including medical imaging, granular physics, colloidal physics, and active matter, require the precise identification and tracking of particle-like objects in images. While many algorithms exist to track particles in diffuse conditions, these often perform poorly when particles are densely packed together—as in, for example, s...

L'accroissement de la population et le développement économique ont conduit à une augmentation de l'urbanisation et à la transformation de zones rurales en paysages urbanisés. Ceci induit un certain nombre de problèmes liés à la gestion de l'eau [XIA 07]. Parmi les principaux problèmes associés à l'urbanisation, on peut mettre en avant l'augmentati...

L'accroissement de la population et le développement économique ont conduit à une augmentation de l'urbanisation et à la transformation de zones rurales en paysages urbanisés. Ceci induit un certain nombre de problèmes liés à la gestion de l'eau [XIA 07]. Parmi les principaux problèmes associés à l'urbanisation, on peut mettre en avant l'augmentati...

Virtual museums have been very popular since the early days of the World Wide Web and many scientific works have been published on this topic. Although the rich variety of possibilities for supporting collaboration among the users of virtual museums, today very few implementations offer support for such kind of activities. This paper aims at settli...

This work studies the problem of GPU thread mapping for a Sierpi\'nski gasket fractal embedded in a discrete Euclidean space of $n \times n$. A block-space map $\lambda: \mathbb{Z}_{\mathbb{E}}^{2} \mapsto \mathbb{Z}_{\mathbb{F}}^{2}$ is proposed, from Euclidean parallel space $\mathbb{E}$ to embedded fractal space $\mathbb{F}$, that maps in $\math...

Flowpaths are significantly affected by land use change and engineered elements across urban catchments. Conventional GIS-based tools for extracting drainage networks were not developed for urban terrains. This work presents Geo-PUMMA, a GIS toolbox to generate vectorial meshes for terrain representation in distributed hydrological modeling, and to...

Background and objective: Infertility is a problem that affects up to 15% of couples worldwide with emotional and physiological implications and semen analysis is the first step in the evaluation of an infertile couple. Indeed the morphology of human sperm cells is considered to be a clinical tool dedicated to the fertility prognosis and serves, ma...

This paper is the first in a series, presenting a new galaxy cluster finder based on a three-dimensional Voronoi Tesselation plus a maximum likelihood estimator, followed by gapping-filtering in radial velocity(VoML+G). The scientific aim of the series is a reassessment of the diversity of optical clusters in the local universe. A mock galaxy datab...

A novel parallel simulation algorithm on the GPU, implemented in CUDA and C++, is presented for the simulation of Brownian particles that display excluded volume repulsion and interact with long and short range forces. When an explicit Euler-Maruyama integration step is performed to take into account the pairwise forces and Brownian motion, particl...

Background and objective:
Published algorithms for classification of human sperm heads are based on relatively small image databases that are not open to the public, and thus no direct comparison is available for competing methods. We describe a gold-standard for morphological sperm analysis (SCIAN-MorphoSpermGS), a dataset of sperm head images wi...

The problem of parallel thread mapping is studied for the case of discrete orthogonal $m$-simplices. The possibility of a $O(1)$ time recursive block-space map $\lambda: \mathbb{Z}^m \mapsto \mathbb{Z}^m$ is analyzed from the point of view of parallel space efficiency and potential performance improvement. The $2$-simplex and $3$-simplex are analyz...

There is a stage in the GPU computing pipeline where a grid of thread-blocks, in \textit{parallel space}, is mapped onto the problem domain, in \textit{data space}. Since the parallel space is restricted to a box type geometry, the mapping approach is typically a $k$-dimensional bounding box (BB) that covers a $p$-dimensional data space. Threads th...

The study of data-parallel domain re-organization and thread-mapping techniques are relevant topics as they can increase the efficiency of GPU computations when working on spatial discrete domains with non-box-shaped geometry. In this work we study the potential benefits of applying a succint data re-organization of a tetrahedral data-parallel doma...

The numerical simulation of phenomena requires a good quality discretization (mesh) of the domain. Depending
on the problem to be simulated, the mesh has to fulfil different quality criteria. Because of geometry
restrictions or point density requirements, several mesh elements might not satisfy the required quality criteria
and sometimes it is also...

The computational cost of transfer matrix methods for the Potts model is
directly related to the problem of \textit{into how many ways can two adjacent
blocks of a lattice be connected}. Answering this question leads to the
generation of a combinatorial set of lattice configurations. This set defines
the \textit{configuration space} of the problem,...

A polyhedral mesh fulfills the Delaunay condition if the vertices of each polyhedron are co-spherical and each polyhedron circum- sphere is point-free. If Delaunay tessellations are used together with the finite volume method, it is not necessary to partition each polyhedron into tetrahedra; co-spherical elements can be used as final elements. This...

Semen analysis is the first step in the evaluation of an infertile couple. Within this process, an accurate and objective morphological analysis becomes more critical as it is based on the correct detection and segmentation of human sperm components. In this paper, we present an improved two-stage framework for detection and segmentation of human s...

The edge-flip technique has been widely used for transforming any existing triangular mesh into a Delaunay mesh. Although several tools for generating Delaunay triangulations are known, there is no one that offers a realtime solution capable of maintaining the Delaunay condition on dynamically changing triangulations and, in particular, one integra...

There is a stage in the GPU computing pipeline where a grid of thread-blocks, or space of computation, is mapped to the problem domain. Normally, the space of computation is a k-dimensional bounding box (BB) that covers a k-dimensional problem. Threads that fall inside the problem domain perform computations and threads that fall outside are discar...

Meshing tools are highly complex software for generating and managing geometrical discretizations. Due to their complexity, they have generally been developed by end users --physicists, forest engineers, mechanical engineers -- with ad hoc methodologies and not by applying well established software engineering practices. Different meshing tools hav...

Meshing tools are highly complex software, and they have usually been developed one at a time and with ad-hoc methodologies. Developing new tools is thus expensive even though there may be similar tools already built. Counting on a systematic method for reusing complex meshing tool components would enhance productivity and enable trying new algorit...

In astronomy, the objective determination of large empty spaces or voids in the spatial distribution of galaxies is part of the characterization of the large scale structure of the universe. This paper proposes a new method to find voids that starting from local longest-edges in a Delaunay triangulation builds the largest possible empty or almost e...

Mixed elements meshes based on the modified octree approach contain several
co-spherical point configurations. While generating Delaunay tessellations to
be used together with the finite volume method, it is not necessary to
partition them into tetrahedra; co-spherical elements can be used as final
elements. This paper presents a study of all co-sp...

Parallel computing has become an important subject in the field of computer science and has proven to be critical when researching high performance solutions. The evolution of computer architectures (multi-core and many-core) towards a higher number of cores can only confirm that parallelism is the method of choice for speeding up an algorithm. In...

There is a stage in the GPU computing pipeline where a grid of thread-blocks
is mapped to the problem domain. Normally, this grid is a k-dimensional
bounding box that covers a k-dimensional problem no matter its shape. Threads
that fall inside the problem domain perform computations, otherwise they are
discarded at runtime. For problems with non-sq...

The transfer-matrix technique is a convenient way for studying strip lattices
in the Potts model since the compu- tational costs depend just on the periodic
part of the lattice and not on the whole. However, even when the cost is
reduced, the transfer-matrix technique is still an NP-hard problem since the
time T(|V|, |E|) needed to compute the matr...

A comprehensive system for facial animation of generic 3D head models driven by speech is presented in this article. In the training stage, audio-visual information is extracted from audio-visual training data, and then used to compute the parameters of a single joint audio-visual hidden Markov model (AV-HMM). In contrast to most of the methods in...

Landscapes are very heterogeneous, which impact the hydrological
processes occurring in the catchments, especially in the modeling of
peri-urban catchments. The Hydrological Response Units (HRUs), resulting
from the intersection of different maps, such as land use, soil types
and geology, and flow networks, allow the representation of these
element...

In this paper, a system for speech-driven animation of generic 3D head models is presented. The system is based on the inversion of a joint Audio-Visual Hidden Markov Model to estimate the visual information from speech data. Estimated visual speech features are used to animate a simple face model. The animation of a more complex head model is then...

Registration methods are used in the meshing field to “adapt” a given mesh to a target domain. Finite element method (FEM)
is applied to the resulting mesh to compute an approximate solution to the system of partial differential equations (PDE)
representing the physical phenomena under study. Prior to FE analysis the Jacobian matrix determinant mus...

The Delaunay edge-flip algorithm is a practical method for transforming any existing triangular mesh S into a mesh T (S) that satisfies the Delaunay condi-tion. Although several implementations of this algo-rithm are known, to the best of our knowledge no par-allel GPU-based implementation has been reported yet. In the present work, we propose a qu...

The edge-flip technique can be used for transform-ing any existing triangular mesh into one that satis-fies the Delaunay condition. Although several imple-mentations for generating Delaunay triangulations are known, to the best of our knowledge no full parallel GPU-based implementation just dedicated to trans-form any existent triangulation into a...

In computer vision, the animation of objects has attracted a lot attention, specially the animations of 3D face models. The animation of face models requires in general to manually adapt each generic movement (open/close mouth) to each specific head geometry. In this work we propose a technique for the animation of any face model avoiding most of t...

It is generally thought within the meshing tool community that object-orientation and other decoupling techniques penalize performance when they are used for building concrete meshing tools. In this paper we show that building a meshing tool with good object-oriented design metrics could not only improve maintainability and all other derived attrib...

The Finite Element Method (FEM) is probably the most used technique to model the mechanic properties of a body. The method needs a subdivision of the body (or domain) to be simulated in simpler geometrical structures. This subdivision is known as a mesh. This chapter gives a short introduction to the FEM, then continues with the most important aspe...

The Finite Element Method (FEM) is probably the most used technique to model the mechanic properties of a body. The method needs a subdivision of the body (or domain) to be simulated in simpler geometrical structures. This subdivision is known as a mesh. This chapter gives a short introduction to the FEM, then continues with the most important aspe...

Once an organization decides to develop a software product line (SPL), one of the first activities that needs to be done is to build a domain model. Here, commonalities and variabilities are identified, as well as the particular charac- teristics that products of the SPL will have. Although there exist some methods proposed for domain modeling, the...

Automated consistency checking of UML models becomes necessary as models grow in size and complexity. Since the UML metamodel does not enforce model consistency, there are no fixed guidelines on how to approach the consistency problem. Current solutions are generally partial. The translation of the metamodel and the user designed model into Descrip...