Eloy Diaz Garcia - Academia.edu (original) (raw)

Papers by Eloy Diaz Garcia

IEEE Transactions on Automatic Control, 2017

Multi-agent systems cooperation to achieve global goals is usually limited by sensing, actuation,... more Multi-agent systems cooperation to achieve global goals is usually limited by sensing, actuation, and communication issues. At the local level, continuous measurement and actuation is only approximated by the use of digital mechanisms that measure and process information in order to compute and update new control input values at discrete time instants. Interaction with other agents or subsystems takes place, in general, through a digital communication channel with limited bandwidth where transmission of continuous-time signals is not possible. Additionally, communication channels may be subject to other imperfections such as time-varying delays. This paper considers the problem of consensus (or synchronization of state trajectories) of multi-agent systems that are described by general linear dynamics and are connected using undirected graphs. An event-triggered consensus protocol is proposed, where each agent implements discretized and decoupled models of the states of its neighbors. This approach not only avoids the need for continuous communication between agents but also provides a decentralized method for transmission of information in the presence of time-varying communication delays where each agent decides its own broadcasting time instants based only on local information. This method gives more flexibility for scheduling information broadcasting compared to periodic and sampled-data implementations. The use of discretized models by each agent allows for a periodic event-triggered strategy where continuous actuation and continuous measurement of the states are not necessary.

Cornell University - arXiv, Jan 12, 2015

In this paper, the problem of bridge consensus is presented and solved. Bridge consensus consists... more In this paper, the problem of bridge consensus is presented and solved. Bridge consensus consists of a network of nodes, some of whom are participating and others are non-participating. The objective is for all the agents to reach average consensus of the participating nodes initial values in a distributed and scalable manner. To do this, the nodes must use the network connections of the non-participating nodes, which act as bridges for information and ignore the initial values of the non-participating nodes. The solution to this problem is made by merging the ideas from estimation theory and consensus theory. By considering the participating nodes has having equal information and the non-participating nodes as having no information, the nodes initial values are transformed into information space. Two consensus filters are run in parallel on the information state and information matrix. Conditions ensuring that the product of the inverse information matrix and the information state of each agent reaches average consensus of the participating agents' initial values is given.

A conflict between rational and autonomous agents is considered. The paper addresses a differenti... more A conflict between rational and autonomous agents is considered. The paper addresses a differential game of protecting a target in the 3-D space. This problem highlights the strong correlation between the highly dynamic scenario, the uncertainty on the behavior of the adversary, and the online and robust computation of state-feedback strategies which guarantee the required level of performance of each player. This work significantly expands previous results around this problem by providing the players' state-feedback saddle-point strategies. Additionally, the continuously differentiable Value function of the multi-agent differential game is obtained and it is shown to be the solution of the Hamilton-Jacobi-Isaacs equation. Finally, the Barrier surface is explicitly obtained and illustrative examples highlight the robustness properties and the guarantees provided by the saddle-point strategies obtained in this paper.

This article provides an introduction to event-triggered coordination for multi-agent average con... more This article provides an introduction to event-triggered coordination for multi-agent average consensus. We provide a comprehensive account of the motivations behind the use of event-triggered strategies for consensus, the methods for algorithm synthesis, the technical challenges involved in establishing desirable properties of the resulting implementations, and their applications in distributed control. We pay special attention to the assumptions on the capabilities of the network agents and the resulting features of the algorithm execution, including the interconnection topology, the evaluation of triggers, and the role of imperfect information. The issues raised in our discussion transcend the specific consensus problem and are indeed characteristic of cooperative algorithms for networked systems that solve other coordination tasks. As our discussion progresses, we make these connections clear, highlighting general challenges and tools to address them widespread in the event-trig...

Journal of Optimization Theory and Applications, 2021

2021 American Control Conference (ACC), 2021

The event-triggered control problem over lossy communication networks is addressed in this paper.... more The event-triggered control problem over lossy communication networks is addressed in this paper. Although packet dropouts have been considered in the implementation of event-triggered controllers, the assumption of protocols that employ acknowledgement messages persists. This paper provides an approach that relaxes such assumption. An event-based controller is implemented at the sensor node of the networked and uncertain system and it transmits feedback measurements to the controller node at asynchronous time instants. The transmitted packets of information are subject to dropouts by the lossy network. We show that the uncertain system can be asymptotically stabilized, that a positive minimum inter-event time exists, and that the proposed approach does not require acknowledgement messages.

2021 American Control Conference (ACC), 2021

An operational relevant conflict between teams of autonomous vehicles in the Beyond Visual Range ... more An operational relevant conflict between teams of autonomous vehicles in the Beyond Visual Range domain is addressed in this paper. Optimal strategies are designed in order for a team of air interceptors to protect a high value asset and block the attacking team at a safe distance from such asset. The attacking agents take specific roles of leader and wingman and also devise their own optimal strategies in order to launch an attack as close as possible from the asset. The problem is formulated as a zero-sum differential game between players with different speed over two stages: the attack and the retreat stages. For each stage the state-feedback optimal strategies of each player are derived in analytical form.

IEEE Transactions on Automatic Control, 2021

In this paper an N-pursuer vs. M-evader team conflict is studied. The differential game of border... more In this paper an N-pursuer vs. M-evader team conflict is studied. The differential game of border defense is addressed and we focus on the game of degree in the region of the state space where the pursuers are able to win. This work extends classical differential game theory to simultaneously address weapon assignments and multi-player pursuit-evasion scenarios. Saddle-point strategies that provide guaranteed performance for each team regardless of the actual strategies implemented by the opponent are devised. The players' optimal strategies require the co-design of cooperative optimal assignments and optimal guidance laws. A representative measure of performance is proposed and the Value function of the game is obtained. It is shown that the Value function is continuous, continuously differentiable, and that it satisfies the Hamilton-Jacobi-Isaacs equation-the curse of dimensionality is overcome and the optimal strategies are obtained. The cases of N = M and N > M are considered. In the latter case, cooperative guidance strategies are also developed in order for the pursuers to exploit their numerical advantage. This work provides a foundation to formally analyze complex and high-dimensional conflicts between teams of N pursuers and M evaders by means of differential game theory. This work has been supported in part by AFOSR LRIR No. 18RQCOR036.

Dynamic Games and Applications, 2018

A zero-sum pursuit-evasion differential game with three players, a Target, an Attacker, and a Def... more A zero-sum pursuit-evasion differential game with three players, a Target, an Attacker, and a Defender, is considered. The Attacker pursues the Target aircraft, while the Defender strives to intercept the Attacker before he reaches the aircraft. In this paper, the game in the state space region where the Attacker prevails is analyzed. The state space region where the Target is vulnerable is characterized and the Attacker's strategy for capturing the Target despite the presence of the Defender is derived. The players' optimal strategies mesh with the previously obtained strategies in the state space region where the Active Target Defense Differential Game is played, and the Defender's presence by virtue of him intercepting the Attacker allows the Target to escape.

Automatica, 2019

This article provides an introduction to event-triggered coordination for multi-agent average con... more This article provides an introduction to event-triggered coordination for multi-agent average consensus. We provide a comprehensive account of the motivations behind the use of event-triggered strategies for consensus, the methods for algorithm synthesis, the technical challenges involved in establishing desirable properties of the resulting implementations, and their applications in distributed control. We pay special attention to the assumptions on the capabilities of the network agents and the resulting features of the algorithm execution, including the interconnection topology, the evaluation of triggers, and the role of imperfect information. The issues raised in our discussion transcend the specific consensus problem and are indeed characteristic of cooperative algorithms for networked systems that solve other coordination tasks. As our discussion progresses, we make these connections clear, highlighting general challenges and tools to address them widespread in the event-triggered control of networked systems.

Dynamic Games and Applications, 2018

A novel pursuit-evasion differential game involving three agents is considered. An Attacker missi... more A novel pursuit-evasion differential game involving three agents is considered. An Attacker missile is pursuing a Target aircraft. The Target aircraft is aided by a Defender missile launched by, say, the wingman, to intercept the Attacker before it reaches the Target aircraft. Thus, a team is formed by the Target and the Defender which cooperate to maximize the separation between the Target aircraft and the point where the Attacker missile is intercepted by the Defender missile, while at the same time the Attacker tries to minimize said distance. A long-range Beyond Visual Range engagement which is in line with current CONcepts of OPeration is envisaged, and it is therefore assumed that the players have simple motion kinematics á la Isaacs. Also, the speed of the Attacker is equal to the speed of the Defender and the latter is interested in point capture. It is also assumed that at all time the Attacker is aware of the Defender's position, i.e., it is a perfect information game. The analytic/closedform solution of the target defense pursuit-evasion differential game delineates the state space region where the Attacker can reach the Target without being intercepted by the Defender, thus disposing of the Game of Kind. The target defense Game of Degree is played in the remaining state space. The analytic solution of the Game of Degree yields the agents' optimal state feedback strategies, that is, the instantaneous heading angles for the Target and the Defender team to maximize the terminal separation between Target and Attacker at the instant of Electronic supplementary material The online version of this article (

Medical physics, Jan 17, 2017

Breast magnetic resonance imaging (MRI) and x-ray mammography are two image modalities widely use... more Breast magnetic resonance imaging (MRI) and x-ray mammography are two image modalities widely used for the early detection and diagnosis of breast diseases in women. The combination of these modalities leads to a more accurate diagnosis and treatment of breast diseases. The aim of this paper is to review the registration between breast MRI and x-ray mammographic images using patient-specific finite element-based biomechanical models. Specifically, a biomechanical model is obtained from the patient's MRI volume and is subsequently used to mimic the mammographic acquisition. Due to the different patient positioning and movement restrictions applied in each image modality, the finite element analysis provides a realistic physics-based approach to perform the breast deformation. In contrast with other reviews, we do not only expose the overall process of compression and registration but we also include main ideas, describe challenges, and provide an overview of the used software in ...

European journal of radiology, 2017

The aim of this paper is to evaluate the spatial glandular volumetric tissue distribution as well... more The aim of this paper is to evaluate the spatial glandular volumetric tissue distribution as well as the density measures provided by Volpara™ using a dataset composed of repeated pairs of mammograms, where each pair was acquired in a short time frame and in a slightly changed position of the breast. We conducted a retrospective analysis of 99 pairs of repeatedly acquired full-field digital mammograms from 99 different patients. The commercial software Volpara™ Density Maps (Volpara Solutions, Wellington, New Zealand) is used to estimate both the global and the local glandular tissue distribution in each image. The global measures provided by Volpara™, such as breast volume, volume of glandular tissue, and volumetric breast density are compared between the two acquisitions. The evaluation of the local glandular information is performed using histogram similarity metrics, such as intersection and correlation, and local measures, such as statistics from the difference image and local ...

International Journal of Control, 2017

This paper presents an event-triggered control and communication framework for the cooperative le... more This paper presents an event-triggered control and communication framework for the cooperative leadertracking problem with communication constraints. Continuous communication among agents is not assumed in this work and decentralized event-based strategies are proposed for agents with heterogeneous linear dynamics. Also, the leader dynamics are unknown and only intermittent measurements of its states are obtained by a subset of the followers. The event-based method not only represents a way to restrict communication among agents, but it also provides a decentralized scheme for scheduling information broadcasts. Notably, each agent is able to determine its own broadcasting instants independently of any other agent in the network. In an extension, the case where transmission of information is affected by time-varying communication delays is addressed. Finally, positive lower-bounds on the inter-event time intervals are obtained in order to show that Zeno behavior does not exist and, therefore, continuous exchange of information is never needed in this framework.

2012 American Control Conference (ACC), 2012

This paper presents a model-based event-triggered (MB-ET) control framework for stabilization of ... more This paper presents a model-based event-triggered (MB-ET) control framework for stabilization of networked systems. The controller and the events are designed in a decentralized manner, based only on local information. The knowledge of a priori model of the interconnected subsystems or agents is used at every controller node to generate estimates of the state of distant subsystems in order to reduce the frequency at which measurements need to be broadcasted. This framework allows for considerable reduction of bandwidth since every agent broadcasts its local information to other agents only when it is necessary, based on the difference between real and estimated variables. The use of models of the systems in the controller nodes not only generalizes the Zero-Order-Hold (ZOH) implementation in traditional event-triggered control schemes but it also provides stability thresholds that are robust to model uncertainties.

Systems & Control: Foundations & Applications, 2014

In this chapter the Model-Based Event-Triggered (MB-ET) framework shown in Chap. 6 is used to max... more In this chapter the Model-Based Event-Triggered (MB-ET) framework shown in Chap. 6 is used to maximize the transmission intervals, but also considering the required control effort and the system response. In other words, we consider the design of optimal control laws and optimal thresholds to trigger communication in the presence of plant-model mismatch by appropriately weighting the system performance, the control effort, and the communication cost. The approach we follow is to optimize the performance of the nominal system, which can be unstable in general, and to ensure robust stability for a given class of model uncertainties and for lack of feedback for extended intervals of time.

Systems & Control: Foundations & Applications, 2014

This chapter provides a formal analysis of nonlinear MB-NCS using nonlinear models. First, result... more This chapter provides a formal analysis of nonlinear MB-NCS using nonlinear models. First, results for two common classes of continuous-time nonlinear MB-NCS are presented where periodic updates are implemented. Then, we study discrete-time nonlinear dissipative systems using output feedback measurements and event-based updates.

Systems & Control: Foundations & Applications, 2014

In this chapter we lay the foundations for the type of networked architecture that we call Model-... more In this chapter we lay the foundations for the type of networked architecture that we call Model-Based Networked Control System (MB-NCS). We also provide a thorough analysis of MB-NCS with state feedback and periodic updates (represented by h). The focus of the chapter is in obtaining conditions that result in a stable networked system. Stabilization depends on the chosen control gain, the accuracy of the model, and the update interval. We derive necessary and sufficient stabilizing conditions for both continuous and discrete-time linear time-invariant systems.

Systems & Control: Foundations & Applications, 2014

In Chap. 8 stability conditions for MB-NCS under popular quantization schemes are derived. The ob... more In Chap. 8 stability conditions for MB-NCS under popular quantization schemes are derived. The objective is to reduce the number of bits needed to transmit feedback measurements to stabilize uncertain systems. When using periodic updates within the MB-NCS framework there are two main parameters that affect the amount of data that is being transmitted, the update interval that dictates how often it is necessary to update the state of the model and the quantization parameter that defines the number of quantization levels and, consequently, the number of bits needed to represent every measurement. When using event-based updates there are also two design parameters that affect stability, the quantization parameter and the threshold value that is used to generate events.

21st Mediterranean Conference on Control and Automation, 2013

This paper presents a practical alternative for the implementation of Model-Based Networked Contr... more This paper presents a practical alternative for the implementation of Model-Based Networked Control Systems (MB-NCS) with intermittent feedback. Our approach does not require continuous communication over a limited bandwidth channel during the closed-loop time intervals; instead, we propose a communication format that implements a fast rate for updating the state of the model. During the closed-loop interval the sensor transmits measurements at a fast rate but without assuming continuous communication. We consider uncertain continuous-time systems and study the state feedback and output feedback cases. For both cases, we provide necessary and sufficient conditions for stability as a function of the update periods.

IEEE Transactions on Automatic Control, 2017

Multi-agent systems cooperation to achieve global goals is usually limited by sensing, actuation,... more Multi-agent systems cooperation to achieve global goals is usually limited by sensing, actuation, and communication issues. At the local level, continuous measurement and actuation is only approximated by the use of digital mechanisms that measure and process information in order to compute and update new control input values at discrete time instants. Interaction with other agents or subsystems takes place, in general, through a digital communication channel with limited bandwidth where transmission of continuous-time signals is not possible. Additionally, communication channels may be subject to other imperfections such as time-varying delays. This paper considers the problem of consensus (or synchronization of state trajectories) of multi-agent systems that are described by general linear dynamics and are connected using undirected graphs. An event-triggered consensus protocol is proposed, where each agent implements discretized and decoupled models of the states of its neighbors. This approach not only avoids the need for continuous communication between agents but also provides a decentralized method for transmission of information in the presence of time-varying communication delays where each agent decides its own broadcasting time instants based only on local information. This method gives more flexibility for scheduling information broadcasting compared to periodic and sampled-data implementations. The use of discretized models by each agent allows for a periodic event-triggered strategy where continuous actuation and continuous measurement of the states are not necessary.

Cornell University - arXiv, Jan 12, 2015

In this paper, the problem of bridge consensus is presented and solved. Bridge consensus consists... more In this paper, the problem of bridge consensus is presented and solved. Bridge consensus consists of a network of nodes, some of whom are participating and others are non-participating. The objective is for all the agents to reach average consensus of the participating nodes initial values in a distributed and scalable manner. To do this, the nodes must use the network connections of the non-participating nodes, which act as bridges for information and ignore the initial values of the non-participating nodes. The solution to this problem is made by merging the ideas from estimation theory and consensus theory. By considering the participating nodes has having equal information and the non-participating nodes as having no information, the nodes initial values are transformed into information space. Two consensus filters are run in parallel on the information state and information matrix. Conditions ensuring that the product of the inverse information matrix and the information state of each agent reaches average consensus of the participating agents' initial values is given.

A conflict between rational and autonomous agents is considered. The paper addresses a differenti... more A conflict between rational and autonomous agents is considered. The paper addresses a differential game of protecting a target in the 3-D space. This problem highlights the strong correlation between the highly dynamic scenario, the uncertainty on the behavior of the adversary, and the online and robust computation of state-feedback strategies which guarantee the required level of performance of each player. This work significantly expands previous results around this problem by providing the players' state-feedback saddle-point strategies. Additionally, the continuously differentiable Value function of the multi-agent differential game is obtained and it is shown to be the solution of the Hamilton-Jacobi-Isaacs equation. Finally, the Barrier surface is explicitly obtained and illustrative examples highlight the robustness properties and the guarantees provided by the saddle-point strategies obtained in this paper.

This article provides an introduction to event-triggered coordination for multi-agent average con... more This article provides an introduction to event-triggered coordination for multi-agent average consensus. We provide a comprehensive account of the motivations behind the use of event-triggered strategies for consensus, the methods for algorithm synthesis, the technical challenges involved in establishing desirable properties of the resulting implementations, and their applications in distributed control. We pay special attention to the assumptions on the capabilities of the network agents and the resulting features of the algorithm execution, including the interconnection topology, the evaluation of triggers, and the role of imperfect information. The issues raised in our discussion transcend the specific consensus problem and are indeed characteristic of cooperative algorithms for networked systems that solve other coordination tasks. As our discussion progresses, we make these connections clear, highlighting general challenges and tools to address them widespread in the event-trig...

Journal of Optimization Theory and Applications, 2021

2021 American Control Conference (ACC), 2021

The event-triggered control problem over lossy communication networks is addressed in this paper.... more The event-triggered control problem over lossy communication networks is addressed in this paper. Although packet dropouts have been considered in the implementation of event-triggered controllers, the assumption of protocols that employ acknowledgement messages persists. This paper provides an approach that relaxes such assumption. An event-based controller is implemented at the sensor node of the networked and uncertain system and it transmits feedback measurements to the controller node at asynchronous time instants. The transmitted packets of information are subject to dropouts by the lossy network. We show that the uncertain system can be asymptotically stabilized, that a positive minimum inter-event time exists, and that the proposed approach does not require acknowledgement messages.

2021 American Control Conference (ACC), 2021

An operational relevant conflict between teams of autonomous vehicles in the Beyond Visual Range ... more An operational relevant conflict between teams of autonomous vehicles in the Beyond Visual Range domain is addressed in this paper. Optimal strategies are designed in order for a team of air interceptors to protect a high value asset and block the attacking team at a safe distance from such asset. The attacking agents take specific roles of leader and wingman and also devise their own optimal strategies in order to launch an attack as close as possible from the asset. The problem is formulated as a zero-sum differential game between players with different speed over two stages: the attack and the retreat stages. For each stage the state-feedback optimal strategies of each player are derived in analytical form.

IEEE Transactions on Automatic Control, 2021

In this paper an N-pursuer vs. M-evader team conflict is studied. The differential game of border... more In this paper an N-pursuer vs. M-evader team conflict is studied. The differential game of border defense is addressed and we focus on the game of degree in the region of the state space where the pursuers are able to win. This work extends classical differential game theory to simultaneously address weapon assignments and multi-player pursuit-evasion scenarios. Saddle-point strategies that provide guaranteed performance for each team regardless of the actual strategies implemented by the opponent are devised. The players' optimal strategies require the co-design of cooperative optimal assignments and optimal guidance laws. A representative measure of performance is proposed and the Value function of the game is obtained. It is shown that the Value function is continuous, continuously differentiable, and that it satisfies the Hamilton-Jacobi-Isaacs equation-the curse of dimensionality is overcome and the optimal strategies are obtained. The cases of N = M and N > M are considered. In the latter case, cooperative guidance strategies are also developed in order for the pursuers to exploit their numerical advantage. This work provides a foundation to formally analyze complex and high-dimensional conflicts between teams of N pursuers and M evaders by means of differential game theory. This work has been supported in part by AFOSR LRIR No. 18RQCOR036.

Dynamic Games and Applications, 2018

A zero-sum pursuit-evasion differential game with three players, a Target, an Attacker, and a Def... more A zero-sum pursuit-evasion differential game with three players, a Target, an Attacker, and a Defender, is considered. The Attacker pursues the Target aircraft, while the Defender strives to intercept the Attacker before he reaches the aircraft. In this paper, the game in the state space region where the Attacker prevails is analyzed. The state space region where the Target is vulnerable is characterized and the Attacker's strategy for capturing the Target despite the presence of the Defender is derived. The players' optimal strategies mesh with the previously obtained strategies in the state space region where the Active Target Defense Differential Game is played, and the Defender's presence by virtue of him intercepting the Attacker allows the Target to escape.

Automatica, 2019

This article provides an introduction to event-triggered coordination for multi-agent average con... more This article provides an introduction to event-triggered coordination for multi-agent average consensus. We provide a comprehensive account of the motivations behind the use of event-triggered strategies for consensus, the methods for algorithm synthesis, the technical challenges involved in establishing desirable properties of the resulting implementations, and their applications in distributed control. We pay special attention to the assumptions on the capabilities of the network agents and the resulting features of the algorithm execution, including the interconnection topology, the evaluation of triggers, and the role of imperfect information. The issues raised in our discussion transcend the specific consensus problem and are indeed characteristic of cooperative algorithms for networked systems that solve other coordination tasks. As our discussion progresses, we make these connections clear, highlighting general challenges and tools to address them widespread in the event-triggered control of networked systems.

Dynamic Games and Applications, 2018

A novel pursuit-evasion differential game involving three agents is considered. An Attacker missi... more A novel pursuit-evasion differential game involving three agents is considered. An Attacker missile is pursuing a Target aircraft. The Target aircraft is aided by a Defender missile launched by, say, the wingman, to intercept the Attacker before it reaches the Target aircraft. Thus, a team is formed by the Target and the Defender which cooperate to maximize the separation between the Target aircraft and the point where the Attacker missile is intercepted by the Defender missile, while at the same time the Attacker tries to minimize said distance. A long-range Beyond Visual Range engagement which is in line with current CONcepts of OPeration is envisaged, and it is therefore assumed that the players have simple motion kinematics á la Isaacs. Also, the speed of the Attacker is equal to the speed of the Defender and the latter is interested in point capture. It is also assumed that at all time the Attacker is aware of the Defender's position, i.e., it is a perfect information game. The analytic/closedform solution of the target defense pursuit-evasion differential game delineates the state space region where the Attacker can reach the Target without being intercepted by the Defender, thus disposing of the Game of Kind. The target defense Game of Degree is played in the remaining state space. The analytic solution of the Game of Degree yields the agents' optimal state feedback strategies, that is, the instantaneous heading angles for the Target and the Defender team to maximize the terminal separation between Target and Attacker at the instant of Electronic supplementary material The online version of this article (

Medical physics, Jan 17, 2017

Breast magnetic resonance imaging (MRI) and x-ray mammography are two image modalities widely use... more Breast magnetic resonance imaging (MRI) and x-ray mammography are two image modalities widely used for the early detection and diagnosis of breast diseases in women. The combination of these modalities leads to a more accurate diagnosis and treatment of breast diseases. The aim of this paper is to review the registration between breast MRI and x-ray mammographic images using patient-specific finite element-based biomechanical models. Specifically, a biomechanical model is obtained from the patient's MRI volume and is subsequently used to mimic the mammographic acquisition. Due to the different patient positioning and movement restrictions applied in each image modality, the finite element analysis provides a realistic physics-based approach to perform the breast deformation. In contrast with other reviews, we do not only expose the overall process of compression and registration but we also include main ideas, describe challenges, and provide an overview of the used software in ...

European journal of radiology, 2017

The aim of this paper is to evaluate the spatial glandular volumetric tissue distribution as well... more The aim of this paper is to evaluate the spatial glandular volumetric tissue distribution as well as the density measures provided by Volpara™ using a dataset composed of repeated pairs of mammograms, where each pair was acquired in a short time frame and in a slightly changed position of the breast. We conducted a retrospective analysis of 99 pairs of repeatedly acquired full-field digital mammograms from 99 different patients. The commercial software Volpara™ Density Maps (Volpara Solutions, Wellington, New Zealand) is used to estimate both the global and the local glandular tissue distribution in each image. The global measures provided by Volpara™, such as breast volume, volume of glandular tissue, and volumetric breast density are compared between the two acquisitions. The evaluation of the local glandular information is performed using histogram similarity metrics, such as intersection and correlation, and local measures, such as statistics from the difference image and local ...

International Journal of Control, 2017

This paper presents an event-triggered control and communication framework for the cooperative le... more This paper presents an event-triggered control and communication framework for the cooperative leadertracking problem with communication constraints. Continuous communication among agents is not assumed in this work and decentralized event-based strategies are proposed for agents with heterogeneous linear dynamics. Also, the leader dynamics are unknown and only intermittent measurements of its states are obtained by a subset of the followers. The event-based method not only represents a way to restrict communication among agents, but it also provides a decentralized scheme for scheduling information broadcasts. Notably, each agent is able to determine its own broadcasting instants independently of any other agent in the network. In an extension, the case where transmission of information is affected by time-varying communication delays is addressed. Finally, positive lower-bounds on the inter-event time intervals are obtained in order to show that Zeno behavior does not exist and, therefore, continuous exchange of information is never needed in this framework.

2012 American Control Conference (ACC), 2012

This paper presents a model-based event-triggered (MB-ET) control framework for stabilization of ... more This paper presents a model-based event-triggered (MB-ET) control framework for stabilization of networked systems. The controller and the events are designed in a decentralized manner, based only on local information. The knowledge of a priori model of the interconnected subsystems or agents is used at every controller node to generate estimates of the state of distant subsystems in order to reduce the frequency at which measurements need to be broadcasted. This framework allows for considerable reduction of bandwidth since every agent broadcasts its local information to other agents only when it is necessary, based on the difference between real and estimated variables. The use of models of the systems in the controller nodes not only generalizes the Zero-Order-Hold (ZOH) implementation in traditional event-triggered control schemes but it also provides stability thresholds that are robust to model uncertainties.

Systems & Control: Foundations & Applications, 2014

In this chapter the Model-Based Event-Triggered (MB-ET) framework shown in Chap. 6 is used to max... more In this chapter the Model-Based Event-Triggered (MB-ET) framework shown in Chap. 6 is used to maximize the transmission intervals, but also considering the required control effort and the system response. In other words, we consider the design of optimal control laws and optimal thresholds to trigger communication in the presence of plant-model mismatch by appropriately weighting the system performance, the control effort, and the communication cost. The approach we follow is to optimize the performance of the nominal system, which can be unstable in general, and to ensure robust stability for a given class of model uncertainties and for lack of feedback for extended intervals of time.

Systems & Control: Foundations & Applications, 2014

This chapter provides a formal analysis of nonlinear MB-NCS using nonlinear models. First, result... more This chapter provides a formal analysis of nonlinear MB-NCS using nonlinear models. First, results for two common classes of continuous-time nonlinear MB-NCS are presented where periodic updates are implemented. Then, we study discrete-time nonlinear dissipative systems using output feedback measurements and event-based updates.

Systems & Control: Foundations & Applications, 2014

In this chapter we lay the foundations for the type of networked architecture that we call Model-... more In this chapter we lay the foundations for the type of networked architecture that we call Model-Based Networked Control System (MB-NCS). We also provide a thorough analysis of MB-NCS with state feedback and periodic updates (represented by h). The focus of the chapter is in obtaining conditions that result in a stable networked system. Stabilization depends on the chosen control gain, the accuracy of the model, and the update interval. We derive necessary and sufficient stabilizing conditions for both continuous and discrete-time linear time-invariant systems.

Systems & Control: Foundations & Applications, 2014

In Chap. 8 stability conditions for MB-NCS under popular quantization schemes are derived. The ob... more In Chap. 8 stability conditions for MB-NCS under popular quantization schemes are derived. The objective is to reduce the number of bits needed to transmit feedback measurements to stabilize uncertain systems. When using periodic updates within the MB-NCS framework there are two main parameters that affect the amount of data that is being transmitted, the update interval that dictates how often it is necessary to update the state of the model and the quantization parameter that defines the number of quantization levels and, consequently, the number of bits needed to represent every measurement. When using event-based updates there are also two design parameters that affect stability, the quantization parameter and the threshold value that is used to generate events.

21st Mediterranean Conference on Control and Automation, 2013

This paper presents a practical alternative for the implementation of Model-Based Networked Contr... more This paper presents a practical alternative for the implementation of Model-Based Networked Control Systems (MB-NCS) with intermittent feedback. Our approach does not require continuous communication over a limited bandwidth channel during the closed-loop time intervals; instead, we propose a communication format that implements a fast rate for updating the state of the model. During the closed-loop interval the sensor transmits measurements at a fast rate but without assuming continuous communication. We consider uncertain continuous-time systems and study the state feedback and output feedback cases. For both cases, we provide necessary and sufficient conditions for stability as a function of the update periods.