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Cosmin Bonchis

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University of Sistan and Baluchestan

Andreas Lintermann

Babes-Bolyai University

UCLouvain (University of Louvain)

Kyandoghere KYAMAKYA

COMSATS Institute of IT Attock Campus

Roberto Garrappa

Università degli Studi di Bari

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Papers by Cosmin Bonchis

$Research paper thumbnail of HPC optimal parallel communication algorithm for the simulation of fractional-order systems$

HPC optimal parallel communication algorithm for the simulation of fractional-order systems

arXiv (Cornell University), Sep 28, 2017

A parallel numerical simulation algorithm is presented for fractionalorder systems involving Capu... more A parallel numerical simulation algorithm is presented for fractionalorder systems involving Caputo-type derivatives, based on the Adams-Bashforth-Moulton (ABM) predictor-corrector scheme. The parallel algorithm is implemented using several different approaches: a pure MPI version, a combination of MPI with OpenMP optimization and a memory saving speedup approach. All tests run on a BlueGene/P cluster, and comparative improvement results for the running time are provided. As an applied experiment, the solutions of a fractionalorder version of a system describing a forced series LCR circuit are numerically computed, depicting cascades of period-doubling bifurcations which lead to the onset of chaotic behavior.

On the heapability of finite partial orders

arXiv (Cornell University), Jun 5, 2017

Define a sequence of elements from a partially ordered set to be heapable if it can be successive... more Define a sequence of elements from a partially ordered set to be heapable if it can be successively inserted as the leaves of a binary tree, not necessarily complete, such that children nodes are always greater or equal than parent nodes. This is a natural binary analog of the notion of a chain in a poset and an easy extension of a definition for integers due to Byers et al. (2011). A set of elements is called heapable if some permutation of its elements is. We investigate the partitioning of sequences from a poset into a minimal number of heapable subsequences. We give an extension of Fulkerson's proof of Dilworth's theorem to decomposition into heapable subsequences which yields as a byproduct a flow-based algorithm for computing such a minimal decomposition.

Improved approximation algorithms for low-density instances of the Minimum Entropy Set Cover Problem

arXiv (Cornell University), Jul 30, 2012

We study the approximability of instances of the minimum entropy set cover problem, parameterized... more We study the approximability of instances of the minimum entropy set cover problem, parameterized by the average frequency of a random element in the covering sets. We analyze an algorithm combining a greedy approach with another one biased towards large sets. The algorithm is controled by the percentage of elements to which we apply the biased approach. The optimal parameter choice has a phase transition around average density e and leads to improved approximation guarantees when average element frequency is less than e.

The language (and series) of Hammersley-type processes

arXiv (Cornell University), Feb 9, 2018

We study languages and formal power series associated to (variants of) the Hammersley process. We... more We study languages and formal power series associated to (variants of) the Hammersley process. We show that the ordinary Hammersley process yields a regular language and the Hammersley tree process yields deterministic context-free (but non-regular) languages. For the Hammersley interval process we show that there are two relevant variants of formal languages. One of them leads to the same language as the ordinary Hammersley tree process. The other one yields non-context-free languages. The results are motivated by the problem of studying the analog of the famous Ulam-Hammersley problem for heapable sequences. Towards this goal we also give an algorithm for computing formal power series associated to the Hammersley process. We employ this algorithm to settle the nature of the scaling constant, conjectured in previous work to be the golden ratio. Our results provide experimental support to this conjecture.

It's Not Whom You Know, It's What You (or Your Friends) Can Do: Succint Coalitional Frameworks for Network Centralities

arXiv (Cornell University), Sep 24, 2019

We investigate the representation of game-theoretic measures of network centrality using a framew... more We investigate the representation of game-theoretic measures of network centrality using a framework that blends a social network representation with the succint formalism of cooperative skill games. We discuss the expressiveness of the new framework and highlight some of its advantages, including a fixed-parameter tractability result for computing centrality measures under such representations. As an application we introduce new network centrality measures that capture the extent to which neighbors of a certain node can help it complete relevant tasks.

A parametric worst-case approach to fairness in cooperative games with transferable utility

Theoretical Computer Science

Worker-to-Task Skill-Based Assignment

Lecture notes in networks and systems, 2023

Mechanism Design With Predictions for Obnoxious Facility Location

arXiv (Cornell University), Dec 19, 2022

We study mechanism design with predictions for the obnoxious facility location problem. We presen... more We study mechanism design with predictions for the obnoxious facility location problem. We present deterministic strategyproof mechanisms that display tradeoffs between robustness and consistency on segments, squares, circles and trees. All these mechanisms are actually group strategyproof, with the exception of the case of squares, where manipulations from coalitions of two agents exist. We prove that these tradeoffs are optimal in the 1-dimensional case.

Edge map response of dilated and reconstructed classical filters

by Ciprian Orhei and Cosmin Bonchis

2020 22nd International Symposium on Symbolic and Numeric Algorithms for Scientific Computing (SYNASC)

Computing a minimal partition of partial orders into heapable subsets

ArXiv, 2017

We investigate the partitioning of partial orders into a minimal number of heapable subsets. We p... more We investigate the partitioning of partial orders into a minimal number of heapable subsets. We prove a characterization result reminiscent of the proof of Dilworth's theorem, which yields as a byproduct a flow-based algorithm for computing such a minimal decomposition. On the other hand, in the particular case of sets and sequences of intervals we prove that this minimal decomposition can be computed by a simple greedy-type algorithm. The paper ends with a couple of open problems related to the analog of the Ulam-Hammersley problem for decompositions of sets and sequences of random intervals into heapable sets.

Worst-Case Fairness in TU-Cooperative Games: A Parametric Approach

Interactive Particle Systems and Random Walks on Hypergraphs

WEB-PS-A Web-based P System Simulator with Query Facilities

Proceedings of the Third …, 2005

Summary. In this paper we present an open-source web-enabled simulator for P systems. We use CLIP... more

Applying Task Farming Model over Grids

$Research paper thumbnail of Numerical simulation algorithm for fractional-order systems implemented in CUDA$

Numerical simulation algorithm for fractional-order systems implemented in CUDA

2020 22nd International Symposium on Symbolic and Numeric Algorithms for Scientific Computing (SYNASC)

A numerical simulation algorithm is presented for fractional-order systems, based on the Adams-Ba... more A numerical simulation algorithm is presented for fractional-order systems, based on the Adams-Bashforth-Moulton (ABM) predictor-corrector scheme. The algorithm is implemented in CUDA, using the specific GPU capabilities. A comparison with the implementation on a BlueGene/P cluster shows the advantages and disadvantages of using this CUDA implementation.

The Language (and Series) of Hammersley-Type Processes

Lecture Notes in Computer Science, 2018

We study languages and formal power series associated to (variants of) the Hammersley process. We... more We study languages and formal power series associated to (variants of) the Hammersley process. We show that the ordinary Hammersley process yields a regular language and the Hammersley tree process yields deterministic context-free (but non-regular) languages. For the Hammersley interval process we show that there are two relevant variants of formal languages. One of them leads to the same language as the ordinary Hammersley tree process. The other one yields non-contextfree languages. The results are motivated by the problem of studying the analog of the famous Ulam-Hammersley problem for heapable sequences. Towards this goal we also give an algorithm for computing formal power series associated to the Hammersley process. We employ this algorithm to settle the nature of the scaling constant, conjectured in previous work to be the golden ratio. Our results provide experimental support to this conjecture.

Kernelization, Proof Complexity and Social Choice

ArXiv, 2021

We display an application of the notions of kernelization and data reduction from parameterized c... more We display an application of the notions of kernelization and data reduction from parameterized complexity to proof complexity: Specifically, we show that the existence of data reduction rules for a parameterized problem having (a). a small-length reduction chain, and (b). small-size (extended) Frege proofs certifying the soundness of reduction steps implies the existence of subexponential size (extended) Frege proofs for propositional formalizations of the given problem. We apply our result to infer the existence of subexponential Frege and extended Frege proofs for a variety of problems. Improving earlier results of Aisenberg et al. (ICALP 2015), we show that propositional formulas expressing (a stronger form of) the Kneser-Lovász Theorem have quasipolynomial size Frege proofs for each constant value of the parameter k. Another notable application of our framework is to impossibility results in computational social choice: we show that, for any fixed number of agents, propositiona...

Interactive Particle Systems on Hypergraphs, Drift Analysis and the WalkSAT algorithm

ArXiv, 2019

We analyze the expected running time of WalkSAT, a well-known local search procedure for satisfia... more We analyze the expected running time of WalkSAT, a well-known local search procedure for satisfiability solving, on satisfiable instances of the k-XOR SAT problem. We obtain estimates of this expected running time by reducing the problem to a setting amenable to classical techniques from drift analysis. A crucial ingredient of this reduction is the definition of (new, explosive) hypergraph versions of interacting particle systems, notably of coalescing and annihilating random walks as well as the voter model. The use of these tools allows to show that the expected running time of WalkSAT depends on structural parameter (we call odd Cheeger drift) of the dual of the formula hypergraph.

On the heapability of finite partial orders

Discret. Math. Theor. Comput. Sci., 2020

We investigate the partitioning of partial orders into a minimal number of heapable subsets. We p... more We investigate the partitioning of partial orders into a minimal number of heapable subsets. We prove a characterization result reminiscent of the proof of Dilworth's theorem, which yields as a byproduct a flow-based algorithm for computing such a minimal decomposition. On the other hand, in the particular case of sets and sequences of intervals we prove that this minimal decomposition can be computed by a simple greedy-type algorithm. The paper ends with a couple of open problems related to the analog of the Ulam-Hammersley problem for decompositions of sets and sequences of random intervals into heapable sets.

Custom Extended Sobel Filters

ArXiv, 2019

Edge detection is widely and fundamental feature used in various algorithms in computer vision to... more Edge detection is widely and fundamental feature used in various algorithms in computer vision to determine the edges in an image. The edge detection algorithm is used to determine the edges in an image which are further used by various algorithms from line detection to machine learning that can determine objects based on their contour. Inspired by new convolution techniques in machine learning we discuss here the idea of extending the standard Sobel kernels, which are used to compute the gradient of an image in order to find its edges. We compare the result of our custom extended filters with the results of the standard Sobel filter and other edge detection filters using different image sets and algorithms. We present statistical results regarding the custom extended Sobel filters improvements.

$Research paper thumbnail of HPC optimal parallel communication algorithm for the simulation of fractional-order systems$

HPC optimal parallel communication algorithm for the simulation of fractional-order systems

arXiv (Cornell University), Sep 28, 2017

A parallel numerical simulation algorithm is presented for fractionalorder systems involving Capu... more A parallel numerical simulation algorithm is presented for fractionalorder systems involving Caputo-type derivatives, based on the Adams-Bashforth-Moulton (ABM) predictor-corrector scheme. The parallel algorithm is implemented using several different approaches: a pure MPI version, a combination of MPI with OpenMP optimization and a memory saving speedup approach. All tests run on a BlueGene/P cluster, and comparative improvement results for the running time are provided. As an applied experiment, the solutions of a fractionalorder version of a system describing a forced series LCR circuit are numerically computed, depicting cascades of period-doubling bifurcations which lead to the onset of chaotic behavior.

On the heapability of finite partial orders

arXiv (Cornell University), Jun 5, 2017

Define a sequence of elements from a partially ordered set to be heapable if it can be successive... more Define a sequence of elements from a partially ordered set to be heapable if it can be successively inserted as the leaves of a binary tree, not necessarily complete, such that children nodes are always greater or equal than parent nodes. This is a natural binary analog of the notion of a chain in a poset and an easy extension of a definition for integers due to Byers et al. (2011). A set of elements is called heapable if some permutation of its elements is. We investigate the partitioning of sequences from a poset into a minimal number of heapable subsequences. We give an extension of Fulkerson's proof of Dilworth's theorem to decomposition into heapable subsequences which yields as a byproduct a flow-based algorithm for computing such a minimal decomposition.

Improved approximation algorithms for low-density instances of the Minimum Entropy Set Cover Problem

arXiv (Cornell University), Jul 30, 2012

We study the approximability of instances of the minimum entropy set cover problem, parameterized... more We study the approximability of instances of the minimum entropy set cover problem, parameterized by the average frequency of a random element in the covering sets. We analyze an algorithm combining a greedy approach with another one biased towards large sets. The algorithm is controled by the percentage of elements to which we apply the biased approach. The optimal parameter choice has a phase transition around average density e and leads to improved approximation guarantees when average element frequency is less than e.

The language (and series) of Hammersley-type processes

arXiv (Cornell University), Feb 9, 2018

We study languages and formal power series associated to (variants of) the Hammersley process. We... more We study languages and formal power series associated to (variants of) the Hammersley process. We show that the ordinary Hammersley process yields a regular language and the Hammersley tree process yields deterministic context-free (but non-regular) languages. For the Hammersley interval process we show that there are two relevant variants of formal languages. One of them leads to the same language as the ordinary Hammersley tree process. The other one yields non-context-free languages. The results are motivated by the problem of studying the analog of the famous Ulam-Hammersley problem for heapable sequences. Towards this goal we also give an algorithm for computing formal power series associated to the Hammersley process. We employ this algorithm to settle the nature of the scaling constant, conjectured in previous work to be the golden ratio. Our results provide experimental support to this conjecture.

It's Not Whom You Know, It's What You (or Your Friends) Can Do: Succint Coalitional Frameworks for Network Centralities

arXiv (Cornell University), Sep 24, 2019

We investigate the representation of game-theoretic measures of network centrality using a framew... more We investigate the representation of game-theoretic measures of network centrality using a framework that blends a social network representation with the succint formalism of cooperative skill games. We discuss the expressiveness of the new framework and highlight some of its advantages, including a fixed-parameter tractability result for computing centrality measures under such representations. As an application we introduce new network centrality measures that capture the extent to which neighbors of a certain node can help it complete relevant tasks.

A parametric worst-case approach to fairness in cooperative games with transferable utility

Theoretical Computer Science

Worker-to-Task Skill-Based Assignment

Lecture notes in networks and systems, 2023

Mechanism Design With Predictions for Obnoxious Facility Location

arXiv (Cornell University), Dec 19, 2022

We study mechanism design with predictions for the obnoxious facility location problem. We presen... more We study mechanism design with predictions for the obnoxious facility location problem. We present deterministic strategyproof mechanisms that display tradeoffs between robustness and consistency on segments, squares, circles and trees. All these mechanisms are actually group strategyproof, with the exception of the case of squares, where manipulations from coalitions of two agents exist. We prove that these tradeoffs are optimal in the 1-dimensional case.

Edge map response of dilated and reconstructed classical filters

by Ciprian Orhei and Cosmin Bonchis

2020 22nd International Symposium on Symbolic and Numeric Algorithms for Scientific Computing (SYNASC)

Computing a minimal partition of partial orders into heapable subsets

ArXiv, 2017

We investigate the partitioning of partial orders into a minimal number of heapable subsets. We p... more We investigate the partitioning of partial orders into a minimal number of heapable subsets. We prove a characterization result reminiscent of the proof of Dilworth's theorem, which yields as a byproduct a flow-based algorithm for computing such a minimal decomposition. On the other hand, in the particular case of sets and sequences of intervals we prove that this minimal decomposition can be computed by a simple greedy-type algorithm. The paper ends with a couple of open problems related to the analog of the Ulam-Hammersley problem for decompositions of sets and sequences of random intervals into heapable sets.

Worst-Case Fairness in TU-Cooperative Games: A Parametric Approach

Interactive Particle Systems and Random Walks on Hypergraphs

WEB-PS-A Web-based P System Simulator with Query Facilities

Proceedings of the Third …, 2005

Summary. In this paper we present an open-source web-enabled simulator for P systems. We use CLIP... more

Applying Task Farming Model over Grids

$Research paper thumbnail of Numerical simulation algorithm for fractional-order systems implemented in CUDA$

Numerical simulation algorithm for fractional-order systems implemented in CUDA

2020 22nd International Symposium on Symbolic and Numeric Algorithms for Scientific Computing (SYNASC)

A numerical simulation algorithm is presented for fractional-order systems, based on the Adams-Ba... more A numerical simulation algorithm is presented for fractional-order systems, based on the Adams-Bashforth-Moulton (ABM) predictor-corrector scheme. The algorithm is implemented in CUDA, using the specific GPU capabilities. A comparison with the implementation on a BlueGene/P cluster shows the advantages and disadvantages of using this CUDA implementation.

The Language (and Series) of Hammersley-Type Processes

Lecture Notes in Computer Science, 2018

We study languages and formal power series associated to (variants of) the Hammersley process. We... more We study languages and formal power series associated to (variants of) the Hammersley process. We show that the ordinary Hammersley process yields a regular language and the Hammersley tree process yields deterministic context-free (but non-regular) languages. For the Hammersley interval process we show that there are two relevant variants of formal languages. One of them leads to the same language as the ordinary Hammersley tree process. The other one yields non-contextfree languages. The results are motivated by the problem of studying the analog of the famous Ulam-Hammersley problem for heapable sequences. Towards this goal we also give an algorithm for computing formal power series associated to the Hammersley process. We employ this algorithm to settle the nature of the scaling constant, conjectured in previous work to be the golden ratio. Our results provide experimental support to this conjecture.

Kernelization, Proof Complexity and Social Choice

ArXiv, 2021

We display an application of the notions of kernelization and data reduction from parameterized c... more We display an application of the notions of kernelization and data reduction from parameterized complexity to proof complexity: Specifically, we show that the existence of data reduction rules for a parameterized problem having (a). a small-length reduction chain, and (b). small-size (extended) Frege proofs certifying the soundness of reduction steps implies the existence of subexponential size (extended) Frege proofs for propositional formalizations of the given problem. We apply our result to infer the existence of subexponential Frege and extended Frege proofs for a variety of problems. Improving earlier results of Aisenberg et al. (ICALP 2015), we show that propositional formulas expressing (a stronger form of) the Kneser-Lovász Theorem have quasipolynomial size Frege proofs for each constant value of the parameter k. Another notable application of our framework is to impossibility results in computational social choice: we show that, for any fixed number of agents, propositiona...

Interactive Particle Systems on Hypergraphs, Drift Analysis and the WalkSAT algorithm

ArXiv, 2019

We analyze the expected running time of WalkSAT, a well-known local search procedure for satisfia... more We analyze the expected running time of WalkSAT, a well-known local search procedure for satisfiability solving, on satisfiable instances of the k-XOR SAT problem. We obtain estimates of this expected running time by reducing the problem to a setting amenable to classical techniques from drift analysis. A crucial ingredient of this reduction is the definition of (new, explosive) hypergraph versions of interacting particle systems, notably of coalescing and annihilating random walks as well as the voter model. The use of these tools allows to show that the expected running time of WalkSAT depends on structural parameter (we call odd Cheeger drift) of the dual of the formula hypergraph.

On the heapability of finite partial orders

Discret. Math. Theor. Comput. Sci., 2020

We investigate the partitioning of partial orders into a minimal number of heapable subsets. We p... more We investigate the partitioning of partial orders into a minimal number of heapable subsets. We prove a characterization result reminiscent of the proof of Dilworth's theorem, which yields as a byproduct a flow-based algorithm for computing such a minimal decomposition. On the other hand, in the particular case of sets and sequences of intervals we prove that this minimal decomposition can be computed by a simple greedy-type algorithm. The paper ends with a couple of open problems related to the analog of the Ulam-Hammersley problem for decompositions of sets and sequences of random intervals into heapable sets.

Custom Extended Sobel Filters

ArXiv, 2019

Edge detection is widely and fundamental feature used in various algorithms in computer vision to... more Edge detection is widely and fundamental feature used in various algorithms in computer vision to determine the edges in an image. The edge detection algorithm is used to determine the edges in an image which are further used by various algorithms from line detection to machine learning that can determine objects based on their contour. Inspired by new convolution techniques in machine learning we discuss here the idea of extending the standard Sobel kernels, which are used to compute the gradient of an image in order to find its edges. We compare the result of our custom extended filters with the results of the standard Sobel filter and other edge detection filters using different image sets and algorithms. We present statistical results regarding the custom extended Sobel filters improvements.