Yusu Wang

Discrete laplace operator on meshed surfaces

In recent years a considerable amount of work in graphics and geometric optimization used tools based on the Laplace-Beltrami operator on a surface. The applications of the Laplacian include mesh editing, surface smoothing, and shape interpolations among others. However, it has been shown [13, 24, 26] that the popular cotangent approximation schemes do not provide convergent point-wise (or even L2) estimates, while many applications rely on point-wise estimation. Existence of such schemes has been an open question [13]. In this paper we propose the first algorithm for approximating the Laplace operator of a surface from a mesh with point-wise convergence guarantees applicable to arbitrary meshed surfaces. We show that for a sufficiently fine mesh over an arbitrary surface, our mesh Laplacian is close to the Laplace-Beltrami operator on the surface at every point of the surface. Moreover, the proposed algorithm is simple and easily implementable. Experimental evidence shows that our algorithm exhibits convergence empirically and compares favorably with cotangentbased methods in providing accurate approximation of the Laplace operator for various meshes.

Extreme Elevation on a 2-Manifold

Given a smoothly embedded 2-manifold in

Near-Linear Time Approximation Algorithms for Curve Simplification

{\Bbb R}^3,

Post-placement voltage island generation under performance requirement

we define the elevation of a point as the height difference to a canonically defined second point on the same manifold. Our definition is invariant under rigid motions and can be used to define features such as lines of discontinuous or continuous but non-smooth elevation. We give an algorithm for finding points of locally maximum elevation, which we suggest mark cavities and protrusions and are useful in matching shapes as for example in protein docking.

Persistent Heat Signature for Pose-oblivious Matching of Incomplete Models

AbstractWe consider the problem of approximating a polygonal curve P under a given error criterion by another polygonal curve P’ whose vertices are a subset of the vertices of P. The goal is to minimize the number of vertices of P’ while ensuring that the error between P’ and P is below a certain threshold. We consider two different error measures: Hausdorff and Frechet. For both error criteria, we present near-linear time approximation algorithms that, given a parameter ε > 0, compute a simplified polygonal curve P’ whose error is less than ε and size at most the size of an optimal simplified polygonal curve with error ε/2. We consider monotone curves in ℝ2 in the case of the Hausdorff error measure under the uniform distance metric and arbitrary curves in any dimension for the Frechet error measure under Lp metrics. We present experimental results demonstrating that our algorithms are simple and fast, and produce close to optimal simplifications in practice.

Fréchet distance for curves, revisited

High power consumption not only leads to short battery life for handheld devices, but also causes on-chip thermal and reliability problems in general. As power consumption is proportional to the square of supply voltage, reducing supply voltage can significantly reduce power consumption. Multi-supply voltage (MSV) has previously been introduced to provide finer-grain power and performance trade-off. In this work we propose a methodology on top of a set of algorithms to exploit non-trivial voltage island boundaries for optimal power versus design cost trade-off under performance requirement. Our algorithms are efficient, robust and error-bounded, and can be flexibly tuned to optimize for various design objectives (e.g., minimal power within a given number of voltage islands, or minimal fragmentation in voltage islands within a given power bound) depending on the design requirement. Our experiment on real industry designs shows a ten-fold improvement of our method over current logical-boundary based industry approach.

Computing Topological Persistence for Simplicial Maps

Although understanding of shape features in the context of shape matching and retrieval has made considerable progress in recent years, the case for partial and incomplete models in presence of pose variations still begs a robust and efficient solution. A signature that encodes features at multi‐scales in a pose invariant manner is more appropriate for this case. The Heat Kernel Signature function from spectral theory exhibits this multi‐scale property. We show how this concept can be merged with the persistent homology to design a novel efficient pose‐oblivious matching algorithm for all models, be they partial, incomplete, or complete. We make the algorithm scalable so that it can handle large data sets. Several test results show the robustness of our approach.

Shape Fitting with Outliers

We revisit the problem of computing the Frechet distance between polygonal curves, focusing on the discrete Frechet distance, where only distance between vertices is considered. We develop efficient approximation algorithms for two natural classes of curves: K-bounded curves and backbone curves, the latter of which are widely used to model molecular structures. We also propose a pseudo-output-sensitive algorithm for computing the discrete Frechet distance exactly. The complexity of the algorithm is a function of the complexity of the free-space boundary, which is quadratic in the worst case, but tends to be lower in practice.

Measuring Distance between Reeb Graphs

Algorithms for persistent homology are well-studied where homomorphisms are induced by inclusion maps. In this paper, we propose a practical algorithm for computing persistence under Z2 coefficients for a (monotone) sequence of general simplicial maps and show how these maps arise naturally in some applications of topological data analysis. A simplicial map can be decomposed into a set of elementary inclusions and vertex collapses--two atomic operations that can be supported efficiently with the notion of simplex annotations for computing persistent homology. A consistent annotation through these atomic operations implies the maintenance of a consistent cohomology basis, hence a homology basis by duality. While the idea of maintaining a cohomology basis through an inclusion is not new, maintaining them through a vertex collapse is new, which constitutes an important atomic operation for simulating simplicial maps. Annotations support the vertex collapse in addition to the usual inclusion quite naturally. Finally, we exhibit an application of this new tool in which we approximate the persistence diagram of a filtration of Rips complexes where vertex collapses are used to tame the blow-up in size.

Approximating gradients for meshes and point clouds via diffusion metric

Given a set