arXiv subjects

Yongjie Yang

Publications and source records attributed to Yongjie Yang.

33 records · Page 2Linked to original sources

arXiv2022

Improved Kernels and Algorithms for Claw and Diamond Free Edge Deletion Based on Refined Observations

In the {claw, diamond}-free edge deletion problem, we are given a graph $G$ and an integer $k>0$, the question is whether there are at most $k$ edges whose deletion results in a graph without claws and diamonds as induced graphs. Based on some refined observations, we propose a kernel of $O(k^3)$ vertices and $O(k^4)$ edges, significantly improving the previous kernel of $O(k^{12})$ vertices and $O(k^{24})$ edges. In addition, we derive an $O^*(3.792^k)$-time algorithm for the {claw, diamond}-free edge deletion problem.

cs.DS↗

arXiv2021

Cooperative control of perpendicular magnetic anisotropy via crystal structure and orientation in single-crystal flexible SrRuO3 membranes

Flexible magnetic materials with robust and controllable perpendicular magnetic anisotropy (PMA) are highly desirable for developing flexible high-performance spintronic devices. However, it is still challenge to fabricate PMA films through current techniques of direct deposition on polymers. Here, we report a facile method for synthesizing single-crystal freestanding SrRuO3 (SRO) membranes with controlled crystal structure and orientation using water-soluble Ca3-xSrxAl2O6 sacrificial layers. Through cooperative effect of crystal structure and orientation engineering, flexible SrRuO3 membranes reveal highly tunable magnetic anisotropy from in-plane to our-of-plane with a remarkable PMA energy of 7.34*106 erg/cm3. Based on the first-principles calculations, it reveals that the underlying mechanism of PMA modulation is intimately correlated with structure-controlled Ru 4d-orbital occupation, as well as the spin-orbital matrix element differences, dependent on the crystal orientation. In addition, there are no obvious changes of the magnetism after 10,000 bending cycles, indicating an excellent magnetism reliability in the prepared films. This work provides a feasible approach to prepare the flexible oxide films with strong and controllable PMA.

cond-mat.str-el↗

arXiv2021

Cycle Extendability of Hamiltonian Strongly Chordal Graphs

In 1990, Hendry conjectured that all Hamiltonian chordal graphs are cycle extendable. After a series of papers confirming the conjecture for a number of graph classes, the conjecture is yet refuted by Lafond and Seamone in 2015. Given that their counterexamples are not strongly chordal graphs and they are all only $2$-connected, Lafond and Seamone asked the following two questions: (1) Are Hamiltonian strongly chordal graphs cycle extendable? (2) Is there an integer $k$ such that all $k$-connected Hamiltonian chordal graphs are cycle extendable? Later, a conjecture stronger than Hendry's is proposed. In this paper, we resolve all these questions in the negative. On the positive side, we add to the list of cycle extendable graphs two more graph classes, namely, Hamiltonian $4$-\textsc{fan}-free chordal graphs where every induced $K_5 - e$ has true twins, and Hamiltonian $\{4\textsc{-fan}, \overline{A} \}$-free chordal graphs.

cs.DM↗

arXiv2020

A Refined Study of the Complexity of Binary Networked Public Goods Games

We study the complexity of several combinatorial problems in the model of binary networked public goods games. In this game, players are represented by vertices in a network, and the action of each player can be either investing or not investing in a public good. The payoff of each player is determined by the number of neighbors who invest and her own action. We study the complexity of computing action profiles that are Nash equilibrium, and those that provide the maximum utilitarian or egalitarian social welfare. We show that these problems are generally NP-hard but become polynomial-time solvable when the given network is restricted to some special domains, including networks with a constant bounded treewidth, and those whose critical clique graphs are forests.

cs.GT↗

arXiv2020

On the Complexity of Constructive Control under Nearly Single-Peaked Preferences

We investigate the complexity of {\sc{Constructive Control by Adding/Deleting Votes}} (CCAV/CCDV) for $r$-approval, Condorcet, Maximin and Copeland$^α$ in $k$-axes and $k$-candidates partition single-peaked elections. In general, we prove that CCAV and CCDV for most of the voting correspondences mentioned above are NP-hard even when~$k$ is a very small constant. Exceptions are CCAV and CCDV for Condorcet and CCAV for $r$-approval in $k$-axes single-peaked elections, which we show to be fixed-parameter tractable with respect to~$k$. In addition, we give a polynomial-time algorithm for recognizing $2$-axes elections, resolving an open problem. Our work leads to a number of dichotomy results. To establish an NP-hardness result, we also study a property of $3$-regular bipartite graphs which may be of independent interest. In particular, we prove that for every $3$-regular bipartite graph, there are two linear orders of its vertices such that the two endpoints of every edge are consecutive in at least one of the two orders.

cs.GT↗

arXiv2018

How Hard Is It to Control A Group?

We consider group identification models in which the aggregation of individual opinions concerning who is qualified in a given society determines the set of socially qualified persons. In this setting, we study the extent to which social qualification can be changed when societies expand, shrink, or partition themselves. The answers we provide are with respect to the computational complexity of the corresponding control problems and fully cover the class of consent aggregation rules introduced by Samet & Schmeidler (2003) as well as procedural rules for group identification. We obtain both polynomial-time solvability results and NP-hardness results. In addition, we also study these problems from the parameterized complexity perspective, and obtain some fixed-parameter tractability results.

cs.GT↗

arXiv2017

Recognizing Linked Domain in Polynomial Time

The celebrated Gibbard-Satterthwaite Theorem states that any surjective social choice function which is defined over the universal domain of preferences and is strategy-proof must be dictatorial. Aswal, Chatterji and Sen generalize the Gibbard-Satterthwaite theorem by showing that the Gibbard-Satterthwaite theorem still holds if the universal domain is replaced with the linked domain. In this note, we show that determining whether an election is linked can be done in polynomial time.

cs.GT↗

arXiv2017

The Control Complexity of $r$-Approval: from the Single-Peaked Case to the General Case

We investigate the complexity of $r$-Approval control problems in $k$-peaked elections, where at most $k$ peaks are allowed in each vote with respect to an order of the candidates. We show that most NP-hardness results in general elections also hold in k-peaked elections even for $k=2,3$. On the other hand, we derive polynomial-time algorithms for some problems for $k=2$. All our NP-hardness results apply to Approval and sincere-strategy preference-based Approval as well. Our study leads to many dichotomy results for the problems considered in this paper, with respect to the values of $k$ and $r$. In addition, we study $r$-Approval control problems from the viewpoint of parameterized complexity and achieve both fixed-parameter tractability results and W-hardness results, with respect to the solution size. Along the way exploring the complexity of control problems, we obtain two byproducts which are of independent interest. First, we prove that every graph of maximum degree 3 admits a specific 2-interval representation where every 2-interval corresponding to a vertex contains a trivial interval and, moreover, 2-intervals may only intersect at the endpoints of the intervals. Second, we develop a fixed-parameter tractable algorithm for a generalized $r$-Set Packing problem with respect to the solution size, where each element in the given universal set is allowed to occur in more than one r-subset in the solution.

cs.GT↗

arXiv2017

Approval Voting with Intransitive Preferences

We extend Approval voting to the settings where voters may have intransitive preferences. The major obstacle to applying Approval voting in these settings is that voters are not able to clearly determine who they should approve or disapprove, due to the intransitivity of their preferences. An approach to address this issue is to apply tournament solutions to help voters make the decision. We study a class of voting systems where first each voter casts a vote defined as a tournament, then a well-defined tournament solution is applied to select the candidates who are assumed to be approved by the voter. Winners are the ones receiving the most approvals. We study axiomatic properties of this class of voting systems and complexity of control and bribery problems for these voting systems.

cs.GT↗

arXiv2016

Further Kernelization of Proper Interval Vertex Deletion: New Observations and Refined Analysis

In the Proper Interval Vertex Deletion problem (PIVD for short), we are given a graph $G$ and an integer parameter $k>0$, and the question is whether there are at most $k$ vertices in $G$ whose removal results in a proper interval graph. It is known that the PIVD problem is fixed-parameter tractable and admits a polynomial but "unreasonably" large kernel of $O(k^{53})$ vertices. A natural question is whether the problem admits a polynomial kernel of "reasonable" size. In this paper, we answer this question by deriving an $O(k^7)$-vertex kernel for the PIVD problem. Our kernelization is based on several new observations and a refined analysis of the kernelization.

cs.DS↗

arXiv2016

A Further Step Towards an Understanding of the Tournament Equilibrium Set

We study some problems pertaining to the tournament equilibrium set (TEQ for short). A tournament $H$ is a TEQ-retentive tournament if there is a tournament $T$ which has a minimal TEQ-retentive set $R$ such that $T[R]$ is isomorphic to $H$. We study TEQ-retentive tournaments and achieve many significant results. In particular, we prove that there are no TEQ-retentive tournaments of size 4, only 2 non-isomorphic TEQ-retentive tournaments of sizes 5 and 6, respectively, and 26 non-isomorphic TEQ-retentive tournaments of size 7. For three tournaments $H_1, H_2$ and $T$, we say $T$ is a $(H_1,H_2)$-TEQ-retentive tournament if $T$ has two minimal TEQ-retentive sets $R_1$ and $R_2$ such that $T[R_1]$ and $T[R_2]$ are isomorphic to $H_1$ and $H_2$, respectively. We show that there are no $(H_1,H_2)$-retentive tournaments for $H_1$ and $H_2$ being small tournaments. Our results imply that Schwartz's Conjecture holds in all tournaments of size at most 14. Finally, we study Schwartz's Conjecture in several classes of tournaments. To achieve these results, we study the relation between (directed) domination graphs of tournaments and TEQ-retentive sets, and derive a number of properties on minimal TEQ-retentive sets.

math.CO↗

arXiv2016

The Complexity of Shelflisting

Optimal shelflisting invites profit maximization to become sensitive to the ways in which purchasing decisions are order-dependent. We study the computational complexity of the corresponding product arrangement problem when consumers are either rational maximizers, use a satisficing procedure, or apply successive choice. The complexity results we report are shown to crucially depend on the size of the top cycle in consumers' preferences over products and on the direction in which alternatives on the shelf are encountered.

cs.GT↗

arXiv2014

Election Attacks with Few Candidates

We investigate the parameterized complexity of strategic behaviors in generalized scoring rules. In particular, we prove that the manipulation, control (all the 22 standard types), and bribery problems are fixed-parameter tractable for most of the generalized scoring rules, with respect to the number of candidates. Our results imply that all these strategic voting problems are fixed-parameter tractable for most of the common voting rules, such as Plurality, r-Approval, Borda, Copeland, Maximin, Bucklin, etc., with respect to the number of candidates.

cs.GT↗

arXiv2014

How Credible is the Prediction of a Party-Based Election?

In a party-based election system, the voters are grouped into parties and all voters of a party are assumed to vote according to the party preferences over the candidates. Hence, once the party preferences are declared the outcome of the election can be determined. However, in the actual election, the members of some "instable" parties often leave their own party to join other parties. We introduce two parameters to measure the credibility of the prediction based on party preferences: Min is the minimum number of voters leaving the instable parties such that the prediction is no longer true, while Max is the maximum number of voters leaving the instable parties such that the prediction remains valid. Concerning the complexity of computing Min and Max, we consider both positional scoring rules (Plurality, Veto, r-Approval and Borda) and Condorcet-consistent rules (Copeland and Maximin). We show that for all considered scoring rules, Min is polynomial-time computable, while it is NP-hard to compute Min for Copeland and Maximin. With the only exception of Borda, Max can be computed in polynomial time for other scoring rules. We have NP-hardness results for the computation of Max under Borda, Maximin and Copeland.

cs.MA↗

arXiv2013

Exact Algorithms for Weighted and Unweighted Borda Manipulation Problems

Both weighted and unweighted Borda manipulation problems have been proved $\mathcal{NP}$-hard. However, there is no exact combinatorial algorithm known for these problems. In this paper, we initiate the study of exact combinatorial algorithms for both weighted and unweighted Borda manipulation problems. More precisely, we propose $O^*((m\cdot 2^m)^{t+1})$time and $O^*(t^{2m})$time\footnote{$O^*()$ is the $O()$ notation with suppressed factors polynomial in the size of the input.} combinatorial algorithms for weighted and unweighted Borda manipulation problems, respectively, where $t$ is the number of manipulators and $m$ is the number of candidates. Thus, for $t=2$ we solve one of the open problems posted by Betzler et al. [IJCAI 2011]. As a byproduct of our results, we show that the {unweighted Borda manipulation} problem admits an algorithm of running time $O^*(2^{9m^2\log{m}})$, based on an integer linear programming technique. Finally, we study the {unweighted Borda manipulation} problem under single-peaked elections and present polynomial-time algorithms for the problem in the case of two manipulators, in contrast to the $\mathcal{NP}$-hardness of this case in general settings.

cs.DS↗