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- Haim Avron, Andrei Sharf, Chen Greif, Daniel Cohen-Or
- ACM Trans. Graph.
- 2010

We introduce an ℓ<sub>1</sub>-sparse method for the reconstruction of a piecewise smooth point set surface. The technique is motivated by recent advancements in sparse signal reconstruction. The assumption underlying our work is that common objects, even geometrically complex ones, can typically be characterized by a rather small number of features.… (More)

The sequence of the 7356 nucleotide [excluding the 3' poly(A)] RNA-1 of tomato black ring virus (TBRV) was determined from overlapping cDNA clones. A putative initiation codon at nucleotide 26l was considered to be the start of an open reading frame which terminates at a UAG codon at position 7053. The predicted translation product is a protein of 2264… (More)

- Tim Rees, Chen Greif
- SIAM J. Scientific Computing
- 2007

We explore a preconditioning technique applied to the problem of solving linear systems arising from primal-dual interior point algorithms in linear and quadratic programming. The preconditioner has the attractive property of improved eigenvalue clustering with increased illconditioning of the (1,1) block of the saddle point matrix. It fits well into the… (More)

- Gene H. Golub, Chen Greif
- SIAM J. Scientific Computing
- 2003

- Chen Greif, Erin Moulding, Dominique Orban
- SIAM Journal on Optimization
- 2014

Interior-point methods feature prominently among numerical methods for inequalityconstrained optimization problems, and involve the need to solve a sequence of linear systems that typically become increasingly ill-conditioned with the iterations. To solve these systems, whose original form has a nonsymmetric 3×3 block structure, it is common practice to… (More)

- David F. Gleich, Chen Greif, James M. Varah
- Numerical Lin. Alg. with Applic.
- 2013

Circulant matrices play a central role in a recently proposed formulation of three-way data computations. In this setting, a three-way table corresponds to a matrix where each “scalar” is a vector of parameters defining a circulant. This interpretation provides many generalizations of results from matrix or vector-space algebra. These results and algorithms… (More)

- Andrei Sharf, Dan A. Alcantara, +4 authors Daniel Cohen-Or
- ACM Trans. Graph.
- 2008

We introduce a volumetric space-time technique for the reconstruction of moving and deforming objects from point data. The output of our method is a four-dimensional space-time solid, made up of spatial slices, each of which is a three-dimensional solid bounded by a watertight manifold. The motion of the object is described as an incompressible flow of… (More)

- Chen Greif, Dominik Schötzau
- Numerical Lin. Alg. with Applic.
- 2007

We introduce a new preconditioning technique for iteratively solving linear systems arising from finite element discretization of the mixed formulation of the time-harmonic Maxwell equations. The preconditioners are motivated by spectral equivalence properties of the discrete operators, but are augmentation-free and Schur complement-free. We provide a… (More)

Abstract. We introduce a new preconditioning technique for the iterative solution of saddle point linear systems with (1,1) blocks that have a high nullity. The preconditioners are block diagonal and are based on augmentation, using symmetric positive definite weight matrices. If the nullity is equal to the number of constraints, the preconditioned matrices… (More)

- Gene H. Golub, Chen Greif, James M. Varah
- SIAM J. Matrix Analysis Applications
- 2005

We consider a positive definite block preconditioner for solving saddle point linear systems. An approach based on augmenting the (1,1) block while keeping its condition number small is described, and algebraic analysis is performed. Ways of selecting the parameters involved are discussed, and analytical and numerical observations are given.