nithin mathew - Academia.edu (original) (raw)
Papers by nithin mathew
We present a new technique for the numerical simulation of axisymmetric systems. This technique a... more We present a new technique for the numerical simulation of axisymmetric systems. This technique avoids the coordinate singularities which often arise when cylindrical or polar-spherical coordinate finite difference grids are used, particularly in simulating tensor partial differential equations like those of 3 + 1 numerical relativity. For a system axisymmetric about the z axis, the basic idea is to use a 3-dimensional Cartesian (x, y, z) coordinate grid which covers (say) the y = 0 plane, but is only one finite-difference-molecule-width thick in the y direction. The field variables in the central y = 0 grid plane can be updated using normal (x, y, z)-coordinate finite differencing, while those in the y = 0 grid planes can be computed from those in the central plane by using the axisymmetry assumption and interpolation. We demonstrate the effectiveness of the approach on a set of fully nonlinear test computations in 3 + 1 numerical general relativity, involving both black holes and collapsing gravitational waves.
In nature, there are examples of large groups of animals that are capable of making optimal colle... more In nature, there are examples of large groups of animals that are capable of making optimal collective-level decisions without the need for global control or information. Understanding the underlying mechanisms of such decentralized decision-making processes may help us to design artificial systems that exhibit some of the desirable properties, like scalability or fault tolerance, that are usually observed in these natural systems. In this paper, we show how a simple social influence mechanism, based on the binary particle swarm optimization algorithm, can make a whole population of agents achieve consensus on one of two possible choices in a completely decentralized way. Furthermore, we show that, if the conditions for achieving consensus are met and each choice is bound to an action that takes time to perform, the population converges to the choice associated with the shortest execution time. We illustrate the applicability of the decision-making mechanism presented in this paper on an example scenario in swarm robotics.
We introduce enhanced directional self-assembly (EDSA) -a novel mechanism for the creation of dir... more We introduce enhanced directional self-assembly (EDSA) -a novel mechanism for the creation of directed connections in a self-assembling morphology growth system. In our approach, a robot inviting a physical connection actively recruits the best located neighboring robot and guides the recruit to the location on its chassis where the connection is required. The proposed mechanism relies on local, highspeed communication between the connection inviting robot and its recruit. We use a hybrid technology that combines radio and infrared to provide local relative positioning information when communication occurs between adjacent robots. Our experiments with real robotic hardware show that EDSA is precise (misalignment of only 1.2 • on average), robust (100% success rate for the experiments in this study) and fast (16.1 seconds on average from a distance of 80 cm). We show how the speed and precision of the new approach enable adaptive recruitment and connection in dynamic environments, a high degree of parallelism, and growth of a moving morphology.
We introduce enhanced directional self-assembly (EDSA) -a novel mechanism for the creation of dir... more We introduce enhanced directional self-assembly (EDSA) -a novel mechanism for the creation of directed connections in a self-assembling morphology growth system. In our approach, a robot inviting a physical connection actively recruits the best located neighboring robot and guides the recruit to the location on its chassis where the connection is required. The proposed mechanism relies on local, highspeed communication between the connection inviting robot and its recruit. We use a hybrid technology that combines radio and infrared to provide local relative positioning information when communication occurs between adjacent robots. Our experiments with real robotic hardware show that EDSA is precise (misalignment of only 1.2 • on average), robust (100% success rate for the experiments in this study) and fast (16.1 seconds on average from a distance of 80 cm). We show how the speed and precision of the new approach enable adaptive recruitment and connection in dynamic environments, a high degree of parallelism, and growth of a moving morphology.
This is part II of a paper devoted to the problem of waveform design for identification of commun... more This is part II of a paper devoted to the problem of waveform design for identification of communication channel parameters, where the waveform is to be embedded in a host signal. We study a quantization-based embedding method and a two-step parameter estimator. The first step is a decoding problem, and the second step is a nonlinear least-squares minimization problem. Estimation
Designing watermarking codes that can withstand geometric and other desynchronization attacks is ... more Designing watermarking codes that can withstand geometric and other desynchronization attacks is a notoriously difficult problem. One may ask whether these difficulties are due to limitations of current codes, or rather to fundamental limitations on achievable performance. We model the attack channel as the cascade of a memoryless channel and a smooth, invertible mapping T θ , θ ∈ Θ n , representing the geometric attack. The decoder does not known the value of θ. We show that under regularity conditions, there exists a universal decoder for this problem, and we explicitly identify it.
This paper presents a preliminary research on extracting the recurring patterns from an image. In... more This paper presents a preliminary research on extracting the recurring patterns from an image. In practice, the recurring patterns have high correlation with the objects that appear recurrently in the image. We assume that the patterns only undergo shift transformation in the image. The main idea of our method is to use the local context information for detecting the 2D distinguishable sub -patterns (DSP) that provide us the spatial information of the patterns in the image with high confidence level. The 2D DSPs are distinctive features of the patterns. The computation is then focused on the signals around those DSPs and eventually grows the DSPs into patterns. To handle the noisy image, we develop dynamic local K -means to quantize the image. The shapes and the position of the DSPs are found in the quantized image. The pattern growing procedure is performed on the original noisy image based on the information provided by the DSPs.
In this paper, we study how an opinion dynamics model can be the core of a collective decision-ma... more In this paper, we study how an opinion dynamics model can be the core of a collective decision-making mechanism for swarm robotics. Our main result is that when opinions represent action choices, the opinion associated with the action that is the fastest to execute spreads in the population. Moreover, the spread of the best choice happens even when only a minority is initially advocating for it. The key elements involved in this process are consensus building and positive feedback. A foraging task that involves collective transport is used to illustrate the potential of the proposed approach.
We present a new technique for the numerical simulation of axisymmetric systems. This technique a... more We present a new technique for the numerical simulation of axisymmetric systems. This technique avoids the coordinate singularities which often arise when cylindrical or polar-spherical coordinate finite difference grids are used, particularly in simulating tensor partial differential equations like those of 3 + 1 numerical relativity. For a system axisymmetric about the z axis, the basic idea is to use a 3-dimensional Cartesian (x, y, z) coordinate grid which covers (say) the y = 0 plane, but is only one finite-difference-molecule-width thick in the y direction. The field variables in the central y = 0 grid plane can be updated using normal (x, y, z)-coordinate finite differencing, while those in the y = 0 grid planes can be computed from those in the central plane by using the axisymmetry assumption and interpolation. We demonstrate the effectiveness of the approach on a set of fully nonlinear test computations in 3 + 1 numerical general relativity, involving both black holes and collapsing gravitational waves.
In nature, there are examples of large groups of animals that are capable of making optimal colle... more In nature, there are examples of large groups of animals that are capable of making optimal collective-level decisions without the need for global control or information. Understanding the underlying mechanisms of such decentralized decision-making processes may help us to design artificial systems that exhibit some of the desirable properties, like scalability or fault tolerance, that are usually observed in these natural systems. In this paper, we show how a simple social influence mechanism, based on the binary particle swarm optimization algorithm, can make a whole population of agents achieve consensus on one of two possible choices in a completely decentralized way. Furthermore, we show that, if the conditions for achieving consensus are met and each choice is bound to an action that takes time to perform, the population converges to the choice associated with the shortest execution time. We illustrate the applicability of the decision-making mechanism presented in this paper on an example scenario in swarm robotics.
We introduce enhanced directional self-assembly (EDSA) -a novel mechanism for the creation of dir... more We introduce enhanced directional self-assembly (EDSA) -a novel mechanism for the creation of directed connections in a self-assembling morphology growth system. In our approach, a robot inviting a physical connection actively recruits the best located neighboring robot and guides the recruit to the location on its chassis where the connection is required. The proposed mechanism relies on local, highspeed communication between the connection inviting robot and its recruit. We use a hybrid technology that combines radio and infrared to provide local relative positioning information when communication occurs between adjacent robots. Our experiments with real robotic hardware show that EDSA is precise (misalignment of only 1.2 • on average), robust (100% success rate for the experiments in this study) and fast (16.1 seconds on average from a distance of 80 cm). We show how the speed and precision of the new approach enable adaptive recruitment and connection in dynamic environments, a high degree of parallelism, and growth of a moving morphology.
We introduce enhanced directional self-assembly (EDSA) -a novel mechanism for the creation of dir... more We introduce enhanced directional self-assembly (EDSA) -a novel mechanism for the creation of directed connections in a self-assembling morphology growth system. In our approach, a robot inviting a physical connection actively recruits the best located neighboring robot and guides the recruit to the location on its chassis where the connection is required. The proposed mechanism relies on local, highspeed communication between the connection inviting robot and its recruit. We use a hybrid technology that combines radio and infrared to provide local relative positioning information when communication occurs between adjacent robots. Our experiments with real robotic hardware show that EDSA is precise (misalignment of only 1.2 • on average), robust (100% success rate for the experiments in this study) and fast (16.1 seconds on average from a distance of 80 cm). We show how the speed and precision of the new approach enable adaptive recruitment and connection in dynamic environments, a high degree of parallelism, and growth of a moving morphology.
This is part II of a paper devoted to the problem of waveform design for identification of commun... more This is part II of a paper devoted to the problem of waveform design for identification of communication channel parameters, where the waveform is to be embedded in a host signal. We study a quantization-based embedding method and a two-step parameter estimator. The first step is a decoding problem, and the second step is a nonlinear least-squares minimization problem. Estimation
Designing watermarking codes that can withstand geometric and other desynchronization attacks is ... more Designing watermarking codes that can withstand geometric and other desynchronization attacks is a notoriously difficult problem. One may ask whether these difficulties are due to limitations of current codes, or rather to fundamental limitations on achievable performance. We model the attack channel as the cascade of a memoryless channel and a smooth, invertible mapping T θ , θ ∈ Θ n , representing the geometric attack. The decoder does not known the value of θ. We show that under regularity conditions, there exists a universal decoder for this problem, and we explicitly identify it.
This paper presents a preliminary research on extracting the recurring patterns from an image. In... more This paper presents a preliminary research on extracting the recurring patterns from an image. In practice, the recurring patterns have high correlation with the objects that appear recurrently in the image. We assume that the patterns only undergo shift transformation in the image. The main idea of our method is to use the local context information for detecting the 2D distinguishable sub -patterns (DSP) that provide us the spatial information of the patterns in the image with high confidence level. The 2D DSPs are distinctive features of the patterns. The computation is then focused on the signals around those DSPs and eventually grows the DSPs into patterns. To handle the noisy image, we develop dynamic local K -means to quantize the image. The shapes and the position of the DSPs are found in the quantized image. The pattern growing procedure is performed on the original noisy image based on the information provided by the DSPs.
In this paper, we study how an opinion dynamics model can be the core of a collective decision-ma... more In this paper, we study how an opinion dynamics model can be the core of a collective decision-making mechanism for swarm robotics. Our main result is that when opinions represent action choices, the opinion associated with the action that is the fastest to execute spreads in the population. Moreover, the spread of the best choice happens even when only a minority is initially advocating for it. The key elements involved in this process are consensus building and positive feedback. A foraging task that involves collective transport is used to illustrate the potential of the proposed approach.