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  • 1.
    Abara, Precious Ugo
    et al.
    Univ Padua, Italy; Tech Univ Munich, Germany.
    Ticozzi, Francesco
    Univ Padua, Italy; Dartmouth Coll, NH 03755 USA.
    Altafini, Claudio
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Spectral Conditions for Stability and Stabilization of Positive Equilibria for a Class of Nonlinear Cooperative Systems2018Ingår i: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 63, nr 2, s. 402-417Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Nonlinear cooperative systems associated to vector fields that are concave or subhomogeneous describe well interconnected dynamics that are of key interest for communication, biological, economical, and neural network applications. For this class of positive systems, we provide conditions that guarantee existence, uniqueness and stability of strictly positive equilibria. These conditions can be formulated directly in terms of the spectral radius of the Jacobian of the system. If control inputs are available, then it is shown how to use state feedback to stabilize an equilibrium point in the interior of the positive orthant.

  • 2.
    Altafini, Claudio
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    A continuous-time dynamical system that can sort agents through distributed protocols2014Ingår i: 2014 IEEEMulti-conference on Systems and Control, Antibes, France: Institute of Electrical and Electronics Engineers (IEEE), 2014, s. 2153-2158Konferensbidrag (Refereegranskat)
    Abstract [en]

    A class of continuous-time dynamical systems able to sort a list of real numbers is introduced in this paper. The dynamical sorting is achieved in a completely distributed manner, by modifying a consensus problem, namely right multiplying a Laplacian matrix by a diagonal matrix of weights that represents the desired order. The sorting obtained is relative, i.e., a conservation law is imposed on the dynamics. It is shown that sorting can be achieved in finite-time even in a globally smooth way.

  • 3.
    Altafini, Claudio
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Involutive flows and discretization errors for nonlinear driftless control systems2017Ingår i: Systems & control letters (Print), ISSN 0167-6911, E-ISSN 1872-7956, Vol. 110, s. 29-37Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In a continuous-time nonlinear driftless control system, an involutive flow is a composition of input profiles that does not excite any Lie bracket. Such flow composition is trivial, as it corresponds to a "forth and back" cyclic motion obtained rewinding the system along the same path. The aim of this paper is to show that, on the contrary, when a (nonexact) discretization of the nonlinear driftless control system is steered along the same trivial input path, it produces a net motion, which is related to the gap between the discretization used and the exact discretization given by a Taylor expansion. These violations of involutivity can be used to provide an estimate of the local truncation error of numerical integration schemes. In the special case in which the state of the driftless control system admits a splitting into shape and phase variables, our result corresponds to saying that the geometric phases of the discretization need not obey an area rule, i.e., even zero-area cycles in shape space can lead to nontrivial geometric phases. (C) 2017 Elsevier B.V. All rights reserved.

  • 4.
    Altafini, Claudio
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Minimal eventually positive realizations of externally positive systems2016Ingår i: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 68, s. 140-147Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It is a well-known fact that externally positive linear systems may fail to have a minimal positive realization. In order to investigate these cases, we introduce the notion of minimal eventually positive realization, for which the state update matrix becomes positive after a certain power. Eventually positive realizations capture the idea that in the impulse response of an externally positive system the state of a minimal realization may fail to be positive, but only transiently. As a consequence, we show that in discrete-time it is possible to use downsampling to obtain minimal positive realizations matching decimated sequences of Markov coefficients of the impulse response. In continuous-time, instead, if the sampling time is chosen sufficiently long, a minimal eventually positive realization leads always to a sampled realization which is minimal and positive.

  • 5.
    Altafini, Claudio
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Nonintegrable discrete-time driftless control systems: geometric phases beyond the area rule2016Ingår i: 2016 IEEE 55th Conference on Decision and Control (CDC), IEEE Press, 2016, s. 4692-4697Konferensbidrag (Refereegranskat)
    Abstract [en]

    In a continuous-time nonlinear driftless control system, a geometric phase is a consequence of nonintegrability of the vector fields, and it describes how cyclic trajectories in shape space induce non-periodic motion in phase space, according to an area rule. The aim of this paper is to shown that geometric phases exist also for discrete-time driftless nonlinear control systems, but that unlike their continuous-time counterpart, they need not obey any area rule, i.e., even zero-area cycles in shape space can lead to nontrivial geometric phases. When the discrete-time system is obtained through Euler discretization of a continuous-time system, it is shown that the zero-area geometric phase corresponds to the gap between the Euler discretization and an exact discretization of the continuous-time system.

  • 6.
    Altafini, Claudio
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Representing externally positive systems through minimal eventually positive realizations2015Ingår i: Proceedings of the IEEE 54th Annual Conference on Decision and Control (CDC),, Institute of Electrical and Electronics Engineers (IEEE), 2015, s. 6385-6390Konferensbidrag (Refereegranskat)
    Abstract [en]

    In order to investigate the cases in which an externally positive discrete-time system fails to have a minimal positive realization, in this paper we introduce the notion of minimal eventually positive realization, fr which the state update matrix becomes positive after a certain power. This property captures the idea that in the impulse response of an externally positive system the state of a minimal realization may fail to be positive, but only transiently. It is shown in the paper that whenever a minimal eventually positive realization exists, then the sequence of Markov parameters of the impulse response admits decimated subsequences for which minimal positive realizations exist and can be obtained by downsampling the eventually positive realization.

  • 7.
    Altafini, Claudio
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    The Geometric Phase of Stock Trading2016Ingår i: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 11, nr 8, s. e0161538-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Geometric phases describe how in a continuous-time dynamical system the displacement of a variable (called phase variable) can be related to other variables (shape variables) undergoing a cyclic motion, according to an area rule. The aim of this paper is to show that geometric phases can exist also for discrete-time systems, and even when the cycles in shape space have zero area. A context in which this principle can be applied is stock trading. A zero-area cycle in shape space represents the type of trading operations normally carried out by high-frequency traders (entering and exiting a position on a fast time-scale), while the phase variable represents the cash balance of a trader. Under the assumption that trading impacts stock prices, even zero-area cyclic trading operations can induce geometric phases, i.e., profits or losses, without affecting the stock quote.

  • 8.
    Altafini, Claudio
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Ceragioli, Francesca
    Politecn Torino, Italy.
    Signed bounded confidence models for opinion dynamics2018Ingår i: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 93, s. 114-125Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The aim of this paper is to modify continuous-time bounded confidence opinion dynamics models so that "changes of opinion" (intended as changes of the sign of the initial states) are never induced during the evolution. Such sign invariance can be achieved by letting opinions of different sign localized near the origin interact negatively, or neglect each other, or even repel each other. In all cases, it is possible to obtain sign-preserving bounded confidence models with state-dependent connectivity and with a clustering behavior similar to that of a standard bounded confidence model. (C) 2018 Elsevier Ltd. All rights reserved.

    Publikationen är tillgänglig i fulltext från 2020-03-28 00:01
  • 9.
    Altafini, Claudio
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Facchetti, Giuseppe
    John Innes Centre, England.
    Metabolic Adaptation Processes That Converge to Optimal Biomass Flux Distributions2015Ingår i: PloS Computational Biology, ISSN 1553-734X, E-ISSN 1553-7358, Vol. 11, nr 9, artikel-id e1004434Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In simple organisms like E. coli, the metabolic response to an external perturbation passes through a transient phase in which the activation of a number of latent pathways can guarantee survival at the expenses of growth. Growth is gradually recovered as the organism adapts to the new condition. This adaptation can be modeled as a process of repeated metabolic adjustments obtained through the resilencings of the non-essential metabolic reactions, using growth rate as selection probability for the phenotypes obtained. The resulting metabolic adaptation process tends naturally to steer the metabolic fluxes towards high growth phenotypes. Quite remarkably, when applied to the central carbon metabolism of E. coli, it follows that nearly all flux distributions converge to the flux vector representing optimal growth, i.e., the solution of the biomass optimization problem turns out to be the dominant attractor of the metabolic adaptation process.

  • 10.
    Altafini, Claudio
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Lini, G.
    SISSA, International School for Advanced Studies,Trieste, Italy; Magneti Marelli S.p.A., Venaria Reale (TO), Italy.
    Achieving unanimous opinions in signed social networks2014Ingår i: Control Conference (ECC), 2014 European, IEEE , 2014, s. 184-189Konferensbidrag (Refereegranskat)
    Abstract [en]

    Being able to predict the outcome of an opinion forming process is an important problem in social network theory. However, even for linear dynamics, this becomes a difficult task as soon as non-cooperative interactions are taken into account. Such interactions are naturally modeled as negative weights on the adjacency matrix of the social network. In this paper we show how the Perron-Frobenius theorem can be used for this task also beyond its standard formulation for cooperative systems. In particular we show how it is possible to associate the achievement of unanimous opinions with the existence of invariant cones properly contained in the positive orthant. These cases correspond to signed adjacency matrices having the eventual positivity property, i.e., such that in sufficiently high powers all negative entries have disappeared. More generally, we show how for social networks the achievement of a, possibily non-unanimous, opinion can be associated to the existence of an invariant cone fully contained in one of the orthants of ℝless thansupgreater thannless than/supgreater than.

  • 11.
    Altafini, Claudio
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan. SISSA, Italy.
    Lini, Gabriele
    SISSA, Italy.
    Predictable Dynamics of Opinion Forming for Networks With Antagonistic Interactions2015Ingår i: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 60, nr 2, s. 342-357Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    For communities of agents which are not necessarily cooperating, distributed processes of opinion forming are naturally represented by signed graphs, with positive edges representing friendly and cooperative interactions and negative edges the corresponding antagonistic counterpart. Unlike for nonnegative graphs, the outcome of a dynamical system evolving on a signed graph is not obvious and it is in general difficult to characterize, even when the dynamics are linear. In this paper, we identify a significant class of signed graphs for which the linear dynamics are however predictable and show many analogies with positive dynamical systems. These cases correspond to adjacency matrices that are eventually positive, for which the Perron-Frobenius property still holds and implies the existence of an invariant cone contained inside the positive orthant. As examples of applications, we determine cases in which it is possible to anticipate or impose unanimity of opinion in decision/voting processes even in presence of stubborn agents, and show how it is possible to extend the PageRank algorithm to include negative links.

  • 12.
    Ballber Torres, Nuria
    et al.
    University of Politecn Cataluna, Spain.
    Altafini, Claudio
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Drug combinatorics and side effect estimation on the signed human drug-target network2016Ingår i: BMC Systems Biology, ISSN 1752-0509, E-ISSN 1752-0509, Vol. 10, nr 74Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Background: The mode of action of a drug on its targets can often be classified as being positive (activator, potentiator, agonist, etc.) or negative (inhibitor, blocker, antagonist, etc.). The signed edges of a drug-target network can be used to investigate the combined mechanisms of action of multiple drugs on the ensemble of common targets. Results: In this paper it is shown that for the signed human drug-target network the majority of drug pairs tend to have synergistic effects on the common targets, i.e., drug pairs tend to have modes of action with the same sign on most of the shared targets, especially for the principal pharmacological targets of a drug. Methods are proposed to compute this synergism, as well as to estimate the influence of the drugs on the side effect of another drug. Conclusions: Enriching a drug-target network with information of functional nature like the sign of the interactions allows to explore in a systematic way a series of network properties of key importance in the context of computational drug combinatorics.

  • 13.
    Ceragioli, Francesca
    et al.
    Politécnico di Torino, Dip. di Mathematica.
    Lindmark, Gustav
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Veibäck, Clas
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Wahlström, Niklas
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Lindfors, Martin
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Altafini, Claudio
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    A bounded confidence model that preserves the signs of the opinions2016Ingår i: Proceedings of the 2016 European Control Conference, Institute of Electrical and Electronics Engineers (IEEE), 2016, s. 543-548Konferensbidrag (Refereegranskat)
    Abstract [en]

    The aim of this paper is to suggest a modification to the usual bounded confidence model of opinion dynamics, so that “changes of opinion” (intended as changes of the sign of the initial state) of an agent are never induced by the dynamics. In order to do so, a bipartite consensus model is used, endowing it with a confidence range. The resulting signed bounded confidence model has a state-dependent connectivity and a behavior similar to its standard counterpart, but in addition it preserves the sign of the opinions by “repelling away” opinions localized near the origin but on different sides with respect to 0.

  • 14.
    Fontan, Angela
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Altafini, Claudio
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Achieving a decision in antagonistic multiagent networks: frustration determines commitment strength2018Ingår i: 2018 IEEE CONFERENCE ON DECISION AND CONTROL (CDC), IEEE , 2018, s. 109-114Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this work we consider a nonlinear interconnected system describing a decision-making process in a community of agents characterized by the coexistence of collaborative and antagonistic interactions. The resulting signed graph is in general not structurally balanced. It is shown in the paper that the decision-making process is affected by the frustration of the signed graph, in the sense that a nontrivial decision can be reached only if the social commitment of the agents is high enough to win the disorder introduced by the frustration in the network. The higher the frustration of the graph, the higher the commitment strength required from the agents.

  • 15.
    Fontan, Angela
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Altafini, Claudio
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Investigating mixed-sign equilibria for nonlinear collective decision-making systems2017Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper we provide necessary conditions for the existence of multiple equilibrium points for a class of non-linear cooperative networked systems with saturating interactions which describe models of collective decision-making. The multiple steady states of the dynamics represent the possible outcomes of a decision process, and, except for one positive and one negative, have all mixed signs. The conditions we obtain can be formulated in terms of the algebraic connectivity of the network and are inspired by Perron-Frobenius arguments. It is also shown that the mixed-sign equilibria are contained in a ball of radius given by the norm of the positive equilibrium point and centered in the origin. Numerical examples are given to illustrate the results.

  • 16.
    Fontan, Angela
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Altafini, Claudio
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Investigating mixed-sign equilibria for nonlinear collective decision-making systems2017Ingår i: Proceedings from the 2017 IEEE 56th Annual Conference on Decision and Control (CDC), December 12-15, 2017, Melbourne, Australia, 2017, s. 781-786Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper we provide necessary conditions for the existence of multiple equilibrium points for a class of non-linear cooperative networked systems with saturating interactions which describe models of collective decision-making. The multiple steady states of the dynamics represent the possible outcomes of a decision process, and, except for one positive and one negative, have all mixed signs. The conditions we obtain can be formulated in terms of the algebraic connectivity of the network and are inspired by Perron-Frobenius arguments. It is also shown that the mixed-sign equilibria are contained in a ball of radius given by the norm of the positive equilibrium point and centered in the origin. Numerical examples are given to illustrate the results.

  • 17.
    Fontan, Angela
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Altafini, Claudio
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Modeling wireless power transfer in a network of smart devices: a compartmental system approach2018Ingår i: 2018 EUROPEAN CONTROL CONFERENCE (ECC), IEEE , 2018, s. 1468-1473Konferensbidrag (Refereegranskat)
    Abstract [en]

    Wireless power transfer technology provides a possible sustainable and cost-effective way to prolong indefinitely the lifetime of networks of smart devices needed in future Internet-of-Things, while equipping them with batteries of limited capacity. In this paper we show that the theory of compartmental systems, positive interconnected systems exchanging mass (here power) and ruled by mass conservation laws, provides a suitable framework to describe wireless power transfer networks. In particular we show that sustainability of the network of smart devices corresponds to each of them being alimented, directly or indirectly, by nodes having an external source of power, condition known as inflow connectivity in the compartmental systems literature. The framework allows to compute the topology which is optimal in terms of maximizing the overall efficiency of the power transfer.

  • 18.
    Fontan, Angela
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Altafini, Claudio
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Multiequilibria analysis for a class of collective decision-making networked systems2018Ingår i: IEEE Transactions on Control of Network Systems, E-ISSN 2325-5870, nr 4, s. 1931-1940Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The models of collective decision-making considered in this paper are nonlinear interconnected cooperative systems with saturating interactions. These systems encode the possible outcomes of a decision process into different steady states of the dynamics. In particular, they are characterized by two main attractors in the positive and negative orthant, representing two choices of agreement among the agents, associated to the Perron-Frobenius eigenvector of the system. In this paper we give conditions for the appearance of other equilibria of mixed sign. The conditions are inspired by Perron-Frobenius theory and are related to the algebraic connectivity of the network. We also show how all these equilibria must be contained in a solid disk of radius given by the norm of the equilibrium point which is located in the positive orthant.

  • 19.
    Fontan, Angela
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Shi, Guodong
    Australian Natl Univ, Australia.
    Hu, Xiaoming
    Royal Inst Technol, Sweden.
    Altafini, Claudio
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Interval Consensus: a novel class of constrained consensus problems for multiagent networks2017Ingår i: 2017 IEEE 56TH ANNUAL CONFERENCE ON DECISION AND CONTROL (CDC), IEEE , 2017Konferensbidrag (Refereegranskat)
    Abstract [en]

    In the consensus problem considered in this paper, each agent can impose a lower and an upper bound on the achievable consensus values. We show that if such state constraints are implemented by saturating the value transmitted to the neighboring nodes, the resulting constrained consensus problem must converge to the intersection of the intervals imposed by the individual agents.

  • 20.
    Giordano, Giulia
    et al.
    Delft Univ Technol, Netherlands.
    Altafini, Claudio
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Interaction sign patterns in biological networks: from qualitative to quantitative criteria2017Ingår i: 2017 IEEE 56TH ANNUAL CONFERENCE ON DECISION AND CONTROL (CDC), IEEE , 2017Konferensbidrag (Refereegranskat)
    Abstract [en]

    In stable biological and ecological networks, the steady-state influence matrix gathers the signs of steady-state responses to step-like perturbations affecting the variables. Such signs are difficult to predict a priori, because they result from a combination of direct effects (deducible from the Jacobian of the network dynamics) and indirect effects. For stable monotone or cooperative networks, the sign pattern of the influence matrix can be qualitatively determined based exclusively on the sign pattern of the system Jacobian. For other classes of networks, we show that a semi-qualitative approach yields sufficient conditions for Jacobians with a given sign pattern to admit a fully positive influence matrix, and we also provide quantitative conditions for Jacobians that are translated eventually nonnegative matrices. We present a computational test to check whether the influence matrix has a constant sign pattern in spite of parameter variations, and we apply this algorithm to quasi-Metzler Jacobian matrices, to assess whether positivity of the influence matrix is preserved in spite of deviations from cooperativity. When the influence matrix is fully positive, we give a simple vertex algorithm to test robust stability. The devised criteria are applied to analyse the steady-state behaviour of ecological and biomolecular networks.

  • 21.
    Giordano, Giulia
    et al.
    Lund University, Sweden.
    Altafini, Claudio
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Qualitative and quantitative responses to press perturbations in ecological networks2017Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, artikel-id 11378Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Predicting the sign of press perturbation responses in ecological networks is challenging, due to the poor knowledge of the strength of the direct interactions among the species, and to the entangled coexistence of direct and indirect effects. We show in this paper that, for a class of networks that includes mutualistic and monotone networks, the sign of press perturbation responses can be qualitatively determined based only on the sign pattern of the community matrix, without any knowledge of parameter values. For other classes of networks, we show that a semi-qualitative approach yields sufficient conditions for community matrices with a given sign pattern to exhibit mutualistic responses to press perturbations; quantitative conditions can be provided as well for community matrices that are eventually nonnegative. We also present a computational test that can be applied to any class of networks so as to check whether the sign of the responses to press perturbations is constant in spite of parameter variations.

  • 22.
    Gonzalez Bosca, Alejandra
    et al.
    Linköpings universitet, Institutionen för systemteknik. Linköpings universitet, Tekniska fakulteten.
    Jafari, Shadi
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelning för neurobiologi. Linköpings universitet, Medicinska fakulteten.
    Zenere, Alberto
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Alenius, Mattias
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelning för neurobiologi. Linköpings universitet, Medicinska fakulteten.
    Altafini, Claudio
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Thermodynamic model of gene regulation for the Or59b olfactory receptor in Drosophila2019Ingår i: PloS Computational Biology, ISSN 1553-734X, E-ISSN 1553-7358, Vol. 15, nr 1, artikel-id e1006709Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Complex eukaryotic promoters normally contain multiple cis-regulatory sequences for different transcription factors (TFs). The binding patterns of the TFs to these sites, as well as the way the TFs interact with each other and with the RNA polymerase (RNAp), lead to combinatorial problems rarely understood in detail, especially under varying epigenetic conditions. The aim of this paper is to build a model describing how the main regulatory cluster of the olfactory receptor Or59b drives transcription of this gene in Drosophila. The cluster-driven expression of this gene is represented as the equilibrium probability of RNAp being bound to the promoter region, using a statistical thermodynamic approach. The RNAp equilibrium probability is computed in terms of the occupancy probabilities of the single TFs of the cluster to the corresponding binding sites, and of the interaction rules among TFs and RNAp, using experimental data of Or59b expression to tune the model parameters. The model reproduces correctly the changes in RNAp binding probability induced by various mutation of specific sites and epigenetic modifications. Some of its predictions have also been validated in novel experiments.

  • 23.
    Kärner Köhler, Anita
    et al.
    Linköpings universitet, Institutionen för samhälls- och välfärdsstudier, Avdelningen för omvårdnad. Linköpings universitet, Medicinska fakulteten.
    Nilsson, Staffan
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för samhällsmedicin. Linköpings universitet, Medicinska fakulteten. Region Östergötland, Primärvårdscentrum, Vårdcentralen Vikbolandet.
    Jaarsma, Tiny
    Linköpings universitet, Institutionen för samhälls- och välfärdsstudier, Avdelningen för omvårdnad. Linköpings universitet, Medicinska fakulteten.
    Tingström, Pia
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för omvårdnad. Linköpings universitet, Medicinska fakulteten.
    Health beliefs about lifestyle habits differ between patients and spouses 1 year after a cardiac event – a qualitative analysis based on the Health Belief Model2017Ingår i: Scandinavian Journal of Caring Sciences, ISSN 0283-9318, E-ISSN 1471-6712, Vol. 31, nr 2, s. 332-341Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    BACKGROUND:

    Spousal concordance on risk factors and lifestyle habits exists and can partly be explained by patients' and spouses' health beliefs and underuse of cardiac rehabilitation. However, there have been very few qualitative comparisons of health beliefs between patients and spouses after a cardiac event.

    AIM:

    To examine and qualitatively compare the health beliefs of patients with coronary heart disease and their spouses about lifestyle habits, 1 year after the cardiac event.

    DESIGN:

    Explorative and descriptive.

    METHOD:

    Semi-structured focus group interviews were conducted with patients (n = 14) 1 year after a cardiac event, as well as individual interviews with spouses (n = 8). The transcriptions underwent a deductive qualitative content analysis, within the framework of the Health Belief Model.

    FINDINGS:

    Patients' and spouses' health beliefs about lifestyle habits qualitatively differed in most predetermined main analytical categories of the Health Belief Model. The patients relied more on their own capacity and the healthcare system than on collaboration with their spouses who instead emphasised the importance of mutual activities to establish lifestyle habits. The spouses therefore experienced problems with different family preferences compared to the patients' wishes. Moreover, only patients believed supervised exercise was beneficial for risk reduction of coronary heart disease and they related barriers for medication to a self-healing body and a meaningless life without relatives and old habits. Patients and spouses agreed that despite the severity of illness, life was captured and that normalisation to a life as usual was possible.

    CONCLUSION:

    The patients' and spouses' qualitatively different health beliefs regarding health-related behaviours imply a new approach. Nurses and associated professionals need to follow-up patients' and spouses' in primary health care to support them in a tailored way, for example in problem-based sessions. Recognition and understanding of their different views and otherness could lead to compromises and goals to work with.

  • 24.
    Lindmark, Gustav
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Altafini, Claudio
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    A driver node selection strategy for minimizing the control energy in complex networks2017Ingår i: IFAC PAPERSONLINE, ELSEVIER SCIENCE BV , 2017, Vol. 50, nr 1, s. 8309-8314Konferensbidrag (Refereegranskat)
    Abstract [en]

    \This paper deals with the problem of controlling linear complex networks in an efficient way, i.e., with limited control energy. A general principle is provided, based on the eigenvalues of the network. It is shown numerically that the cost of controlling a network grows with the (absolute value of the) real part of the eigenvalues of the adjacency matrix. Constructive rules for driver node selection are also provided, based on the (weighted) topology of the network. In particular, we show that the key to have an energetically efficient driver node placement strategy is to use the skewness of the outdegree versus indegree distributions of the network, a topological property not associated before to controllability. (C) 2017, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.

  • 25.
    Lindmark, Gustav
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Altafini, Claudio
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Combining centrality measures for control energy reduction in network controllability problems2019Ingår i: Proceedings of the 2019 European Control Conference (ECC), Institute of Electrical and Electronics Engineers (IEEE), 2019, s. 1518-1523Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper investigates the problem of controlling a complex network with reduced control energy. Two centrality measures are defined, one related to the energy that a control, placed on a node, can exert on the entire network, and the other related to the energy that the network exerts on a node. We show that by combining these two centrality measures conflicting control energy requirements, like minimizing the average energy needed to steer the state in any direction and the energy needed for the worst direction, can be simultaneously taken into account. From an algebraic point of view, the node ranking that we obtain from the combination of our centrality measures is related to the non-normality of the adjacency matrix of the graph.

  • 26.
    Lindmark, Gustav
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Altafini, Claudio
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Combining centrality measures for control energy reduction in network controllability problems2019Ingår i: Proceedings of the 2019 European Control Conference (ECC), Institute of Electrical and Electronics Engineers (IEEE), 2019, s. 1518-1523Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper investigates the problem of controlling a complex network with reduced control energy. Two centrality measures are defined, one related to the energy that a control, placed on a node, can exert on the entire network, and the other related to the energy that the network exerts on a node. We show that by combining these two centrality measures conflicting control energy requirements, like minimizing the average energy needed to steer the state in any direction and the energy needed for the worst direction, can be simultaneously taken into account. From an algebraic point of view, the node ranking that we obtain from the combination of our centrality measures is related to the non-normality of the adjacency matrix of the graph.

  • 27.
    Lindmark, Gustav
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Altafini, Claudio
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Controllability of complex networks with unilateral inputs2017Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, artikel-id 1824Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we study the problem of controlling complex networks with unilateral controls, i.e., controls which can assume only positive or negative values, not both. Given a complex network represented by the adjacency matrix A, an algorithm is developed that constructs an input matrix B such that the resulting system (A, B) is controllable with a near minimal number of unilateral control inputs. This is made possible by a reformulation of classical conditions for controllability that casts the minimal unilateral input selection problem into well known optimization problems. We identify network properties that make unilateral controllability relatively easy to achieve as compared to unrestricted controllability. The analysis of the network topology for instance allows us to establish theoretical bounds on the minimal number of controls required. For various categories of random networks as well as for a number of real-world networks these lower bounds are often achieved by our heuristics.

  • 28.
    Lindmark, Gustav
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Altafini, Claudio
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Minimum energy control for complex networks2018Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, artikel-id 3188Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The aim of this paper is to shed light on the problem of controlling a complex network with minimal control energy. We show first that the control energy depends on the time constant of the modes of the network, and that the closer the eigenvalues are to the imaginary axis of the complex plane, the less energy is required for complete controllability. In the limit case of networks having all purely imaginary eigenvalues (e.g. networks of coupled harmonic oscillators), several constructive algorithms for minimum control energy driver node selection are developed. A general heuristic principle valid for any directed network is also proposed: the overall cost of controlling a network is reduced when the controls are concentrated on the nodes with highest ratio of weighted outdegree vs indegree.

  • 29.
    Lindmark, Gustav
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Altafini, Claudio
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Minimum energy control for networks of coupled harmonic oscillators2017Ingår i: IFAC PAPERSONLINE, ELSEVIER SCIENCE BV , 2017, Vol. 50, nr 1, s. 8321-8326Konferensbidrag (Refereegranskat)
    Abstract [en]

    The aim of this paper is to investigate the problem of selecting driver nodes enabling the control of a network with minimal control energy. The networks we are interested in are coupled harmonic oscillators, i.e., networks in which the eigenvalues are all purely imaginary. For them, several criteria for driver node selection are presented, based on the different measures of control energy considered in this context. The constructive algorithms we develop for these criteria are normally solving the problem in a heuristic way, although in one case the exact solution can be computed efficiently regardless of size. (C) 2017, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.

  • 30.
    Lindmark, Gustav
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Altafini, Claudio
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Positive Controllability of Large-Scale Networks2016Ingår i: Proceedings of the 2016 European Control Conference, Institute of Electrical and Electronics Engineers (IEEE), 2016, s. 819-824Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we study the problem of controlling large scale networks with controls which can assume only positive values. Given an adjacency matrix A, an algorithm is developed that constructs an input matrix B with a minimal number of columns such that the resulting system (A, B) is positively controllable. The algorithm combines the graphical methods used for structural controllability analysis with the theory of positive linear dependence. The number of control inputs guaranteeing positive controllability is near optimal.

  • 31.
    Lindmark, Gustav
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Altafini, Claudio
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Topological aspects of controlling large scale networks with unilateral inputs2017Ingår i: IFAC PAPERSONLINE, ELSEVIER SCIENCE BV , 2017, Vol. 50, nr 1, s. 8315-8320Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we study the problem of controlling complex networks with unilateral controls, i.e., controls which can assume only positive or negative values, not both. Given a network with linear dynamics represented by the adjacency matrix A, we seek to understand the minimal number of unilateral controls that renders the network controllable. This problem has structural properties that for instance allows us to establish theoretical bounds and identify key topological properties that makes a network relatively easy to control with unilateral controls as compared to unrestricted controls. We find that the structure of the left null space of A is particularly important to this end. In a computational study we find that the network topology largely determines the number of unilateral controls and that the derived lower bounds often are achieved with heuristic methods. (C) 2017, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.

  • 32.
    Mazzolini, Monica
    et al.
    International School for Advanced Studies, Trieste, Italy.
    Facchetti, Giuseppe
    International School for Advanced Studies, Trieste, Italy.
    Andolfi, Laura
    Cluster for Biomedicine, Trieste, Italy.
    Proietti Zaccaria, Remo
    Istituto Italiano di Tecnologia, Genova, Italy.
    Tuccio, Salvatore
    Istituto Italiano di Tecnologia, Genova, Italy.
    Treu, Johannes
    Rapp OptoElectronic, Wedel, Germany.
    Altafini, Claudio
    International School for Advanced Studies, Trieste, Italy.
    Di Fabrizio, Enzo
    King Abdullah University of Science and Technology, Thuwal, Saudi Arabia.
    Torre, Vincent
    International School for Advanced Studies, Trieste, Italy.
    The phototransduction machinery in the rod outer segment has a strong efficacy gradient2015Ingår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 112, nr 20, s. E2715-E272Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Rod photoreceptors consist of an outer segment (OS) and an inner segment. Inside the OS a biochemical machinery transforms the rhodopsin photoisomerization into electrical signal. This machinery has been treated as and is thought to be homogenous with marginal inhomogeneities. To verify this assumption, we developed a methodology based on special tapered optical fibers (TOFs) to deliver highly localized light stimulations. By using these TOFs, specific regions of the rod OS could be stimulated with spots of light highly confined in space. As the TOF is moved from the OS base toward its tip, the amplitude of saturating and single photon responses decreases, demonstrating that the efficacy of the transduction machinery is not uniform and is 5–10 times higher at the base than at the tip. This gradient of efficacy of the transduction machinery is attributed to a progressive depletion of the phosphodiesterase along the rod OS. Moreover we demonstrate that, using restricted spots of light, the duration of the photoresponse along the OS does not increase linearly with the light intensity as with diffuse light.

  • 33.
    Precious, Ugo Abara
    et al.
    Univversity of Padova, Italy.
    Ticozzi, Francesco
    Univversity of Padova, Italy.
    Altafini, Claudio
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Existence, uniqueness and stability properties of positive equilibria for a class of nonlinear cooperative systems2015Ingår i: Proceedings of 54th IEEE Conference on Decision and Control (CDC), Institute of Electrical and Electronics Engineers (IEEE), 2015, s. 4406-4411Konferensbidrag (Refereegranskat)
    Abstract [en]

    We provide conditions that guarantee existence, uniqueness and stability of strictly positive equilibria for nonlinear cooperative systems associated to vector fields that are concave or subhomogeneous. This class of positive systems describes well interconnected dynamics that are of key interest for communication, biological, economical and neural network applications. These conditions can be formulated directly in terms of the spectral radius of the Jacobian of the system, and do not require to use constant inputs to move the equilibrium point from the origin to the interior of the positive orthant.

  • 34.
    Shi, Guodong
    et al.
    Australian Natl Univ, Australia.
    Altafini, Claudio
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Baras, John S.
    Univ Maryland, MD 20742 USA; Univ Maryland, MD 20742 USA.
    Algebraic-Graphical Approach for Signed Dynamical Networks2017Ingår i: 2017 IEEE 56TH ANNUAL CONFERENCE ON DECISION AND CONTROL (CDC), IEEE , 2017Konferensbidrag (Refereegranskat)
    Abstract [en]

    A signed network is a network with each link associated with a positive or negative sign. Models for nodes interacting over such signed networks, where two types of interactions are defined along the positive and negative links, respectively, arise from various biological, social, political, and economical systems. Starting from standard consensus dynamics, there are two basic types of negative interactions along negative links, namely state flipping or relative-state flipping. In this paper, we provide an algebraic-graphical method serving as a systematic tool of studying these dynamics over signed networks. Utilizing generalized Perron-Frobenius theory, graph theory, and elementary algebraic recursions, we show this method is useful to establish a series of basic convergence results for dynamics over signed networks.

  • 35.
    Shi, Guodong
    et al.
    Univ Sydney, Australia; Australian Natl Univ, Australia.
    Altafini, Claudio
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Baras, John S.
    Univ Maryland, USA.
    Dynamics over Signed Networks2019Ingår i: SIAM Review, ISSN 0036-1445, E-ISSN 1095-7200, Vol. 61, nr 2, s. 229-257Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A signed network is a network in which each link is associated with a positive or negative sign. Models for nodes interacting over such signed networks arise from various biological, social, political, and economic systems. As modifications to the conventional DeGroot dynamics for positive links, two basic types of negative interactions along negative links, namely, the opposing rule and the repelling rule, have been proposed and studied in the literature. This paper reviews a few fundamental convergence results for such dynamics over deterministic or random signed networks under a unified algebraic-graphical method. We show that a systematic tool for studying node state evolution over signed networks can be obtained utilizing generalized Perron-Frobenius theory, graph theory, and elementary algebraic recursions.

  • 36.
    Ugo Abara, Precious
    et al.
    Department of Information Engineering, University of Padova, Italy.
    Ticozzi, Francesco
    Department of Information Engineering, University of Padova, Italy.
    Altafini, Claudio
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    An infinitesimal characterization of nonlinear contracting interference functions2016Ingår i: 2016 IEEE 55th Conference on Decision and Control (CDC), IEEE Press, 2016, s. 5257-5262Konferensbidrag (Refereegranskat)
    Abstract [en]

    Contractive interference functions are a subclass of the standard interference functions used in the design and analysis of distributed power control algorithms for wireless networks. Their peculiarity is that for the resulting positive system the existence and global asymptotic stability of a unique positive equilibrium point is guaranteed. In this paper we give an infinitesimal characterization of nonlinear contractiveinterference functions in terms of the spectral radius of the Jacobian linearization at any point in the positive orthant. The condition we obtain, that the spectral radius is always less than 1, extends to the nonlinear case an equivalent property of linear interference functions, and leads to a Jacobian characterization similar to the one commonly used in contraction analysis of nonlinear systems.

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