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Chuan Yi Tang - One of the best experts on this subject based on the ideXlab platform.
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Balancing minimum spanning trees and multiple-source minimum routing cost spanning trees on metric graphs
Information Processing Letters, 2006Co-Authors: Chung-ming Lin, Yin Te Tsai, Chuan Yi TangAbstract:Both the building cost and the multiple-source routing cost are important considerations in construction of a network system. A spanning tree with minimum building cost among all spanning trees is called a minimum spanning tree (MST), and a spanning tree with minimum k-source routing cost among all spanning trees is called a k-source minimum routing cost spanning tree (k-MRCT). This paper proposes an algorithm to construct a spanning tree T for a metric graph G with a source vertex set S such that the building cost of T is at most 1 + 2/(α - 1) times of that of an MST of G, and the k-source routing cost of T is at most α(1+2(k-1)(n - 2)/k(n + k - 2)) times of that of a k-MRCT of G with respect to S, where α > 1, k = |S| and n is the number of vertices of G.
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a polynomial time approximation scheme for minimum routing cost spanning trees
SIAM Journal on Computing, 1999Co-Authors: Giuseppe Lancia, R Ravi, Vineet Bafna, Kunmao Chao, Chuan Yi TangAbstract:Given an undirected graph with nonnegative costs on the edges, the routing cost of any of its spanning trees is the sum over all pairs of vertices of the cost of the path between the pair in the tree. Finding a spanning tree of minimum routing cost is NP-hard, even when the costs obey the triangle inequality. We show that the general case is in fact reducible to the metric case and present a polynomial-time approximation scheme valid for both versions of the problem. In particular, we show how to build a spanning tree of an n-vertex weighted graph with routing cost at most $(1+\epsilon)$ of the minimum in time $O(n^{O({\frac{1}{\epsilon}}% )})$. Besides the obvious connection to network design, trees with small routing cost also find application in the construction of good multiple sequence alignments in computational biology. The communication cost spanning tree problem is a generalization of the minimum routing cost tree problem where the routing costs of different pairs are weighted by different requirement amounts. We observe that a randomized O(log n log log n)-approximation for this problem follows directly from a recent result of Bartal, where n is the number of nodes in a metric graph. This also yields the same approximation for the generalized sum-of-pairs alignment problem in computational biology.
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a polynomial time approximation scheme for minimum routing cost spanning trees
Symposium on Discrete Algorithms, 1998Co-Authors: Giuseppe Lancia, R Ravi, Vineet Bafna, Kunmao Chao, Chuan Yi TangAbstract:Given an undirected graph with nonnegative costs on the edges, the routing cost of any of its spanning trees is the sum over all pairs of vertices of the cost of the path between the pair in the tree. Finding a spanning tree of minimum routing cost is NP-hard, even when the costs obey the triangle inequality. We show that the general case is in fact reducible to the metric case and present a polynomial-time approximation scheme valid for both versions of the problem. In particular, we show how to build a spanning tree of an n-vertex weighted graph with routing cost at most (1 +) of the minimum in time O(n O( 1 ) ). Besides the obvious connection to network design, trees with small routing cost also nd application in the construction of good multiple sequence alignments in computational biology. The communication cost spanning tree problem is a generalization of the minimum routing cost tree problem where the routing costs of dierent pairs are weighted by dierent requirement amounts. We observe that a randomized O(logn log logn)-approximation for this problem follows directly from a recent result of Bartal, where n is the number of nodes in a metric graph. This also yields the same approximation for the generalized sum-of-pairs alignment problem in computational biology.
Jan Steinhoff - One of the best experts on this subject based on the ideXlab platform.
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next to next to leading order gravitational spin orbit coupling via the effective field theory for spinning objects in the post newtonian scheme
Journal of Cosmology and Astroparticle Physics, 2016Co-Authors: Michele Levi, Jan SteinhoffAbstract:We implement the effective field theory for gravitating spinning objects in the post-Newtonian scheme at the next-to-next-to-leading order level to derive the gravitational spin-orbit interaction potential at the third and a half post-Newtonian order for rapidly rotating compact objects. From the next-to-next-to-leading order interaction potential, which we obtain here in a Lagrangian form for the first time, we derive straightforwardly the corresponding Hamiltonian. The spin-orbit sector constitutes the most elaborate spin dependent sector at each order, and accordingly we encounter a proliferation of the relevant Feynman diagrams, and a significant increase of the computational complexity. We present in detail the evaluation of the interaction potential, going over all contributing Feynman diagrams. The computation is carried out in terms of the ``nonrelativistic gravitational'' fields, which are advantageous also in spin dependent sectors, together with the various gauge choices included in the effective field theory for gravitating spinning objects, which also optimize the calculation. In addition, we automatize the effective field theory computations, and carry out the automated computations in parallel. Such automated effective field theory computations would be most useful to obtain higher order post-Newtonian corrections. We compare our Hamiltonian to the ADM Hamiltonian, and arrive at a complete agreement between the ADM and effective field theory results. Finally, we provide Hamiltonians in the center of mass frame, and complete gauge invariant relations among the binding energy, angular momentum, and orbital frequency of an inspiralling binary with generic compact spinning components to third and a half post-Newtonian order. The derivation presented here is essential to obtain further higher order post-Newtonian corrections, and to reach the accuracy level required for the successful detection of gravitational radiation.
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next to next to leading order gravitational spin orbit coupling via the effective field theory for spinning objects in the post newtonian scheme
arXiv: General Relativity and Quantum Cosmology, 2015Co-Authors: Michele Levi, Jan SteinhoffAbstract:We implement the effective field theory for gravitating spinning objects in the post-Newtonian scheme at the next-to-next-to-leading order level to derive the gravitational spin-orbit interaction potential at the third and a half post-Newtonian order for rapidly rotating compact objects. From the next-to-next-to-leading order interaction potential, which we obtain here in a Lagrangian form for the first time, we derive straightforwardly the corresponding Hamiltonian. The spin-orbit sector constitutes the most elaborate spin dependent sector at each order, and accordingly we encounter a proliferation of the relevant Feynman diagrams, and a significant increase of the computational complexity. We present the evaluation of the interaction potential, going over contributing Feynman diagrams. The computation is carried out in terms of the nonrelativistic gravitational fields, together with the various gauge choices included in the effective field theory for gravitating spinning objects, which optimize the calculation. In addition, we automatize the effective field theory computations, and carry out the automated computations in parallel. Such automated effective field theory computations would be most useful to obtain higher order post-Newtonian corrections. We compare our Hamiltonian to the ADM Hamiltonian, and arrive at a complete agreement between the ADM and effective field theory results. We provide complete gauge invariant relations among the binding energy, angular momentum, and orbital frequency of an inspiralling binary with generic compact spinning components to third and a half post-Newtonian order. The derivation presented here is essential to obtain further higher order post-Newtonian corrections, and to reach the accuracy level required for the successful detection of gravitational radiation.
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an effective field theory for gravitating spinning objects in the post newtonian scheme
arXiv: General Relativity and Quantum Cosmology, 2015Co-Authors: Michele Levi, Jan SteinhoffAbstract:An effective field theory for gravitating spinning objects in the post-Newtonian approximation is formulated in the context of the binary inspiral problem. We aim at an effective action, where all field modes below the orbital scale are integrated out. We spell out the relevant degrees of freedom, in particular the rotational ones, and the associated symmetries. Building on these symmetries, we introduce the minimal coupling part of the point particle action in terms of gauge rotational variables. We then proceed to construct the spin-induced nonminimal couplings, where we obtain the leading order couplings to all orders in spin for the first time. We specify to a gauge for the rotational variables, where the unphysical degrees of freedom are eliminated already from the Feynman rules, and all the orbital field modes are conveniently integrated out. The equations of motion of spin are then directly obtained via a proper variation of the action, and they take on a simple form. We implement this effective field theory for spin to derive all spin dependent potentials up to next-to-leading order to quadratic level in spin, namely up to the third post-Newtonian order for rapidly rotating compact objects. For the implementations we use the nonrelativistic gravitational field decomposition, which is found here to eliminate higher-loop Feynman diagrams also in spin dependent sectors, and facilitates derivations. Finally, the corresponding Hamiltonians are also straightforwardly obtained from the potentials derived via this formulation. Thus, the formulation is ideal for the treatment of further higher order spin dependent sectors.
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spinning gravitating objects in the effective field theory in the post newtonian scheme
arXiv: General Relativity and Quantum Cosmology, 2015Co-Authors: Michele Levi, Jan SteinhoffAbstract:We introduce a formulation for spinning gravitating objects in the effective field theory in the post-Newtonian scheme in the context of the binary inspiral problem. We aim at an effective action, where all field modes below the orbital scale are integrated out. We spell out the relevant degrees of freedom, in particular the rotational ones, and the associated symmetries. Building on these symmetries, we introduce the minimal coupling part of the point particle action in terms of gauge rotational variables, and construct the spin-induced nonminimal couplings, where we obtain the leading order couplings to all orders in spin. We specify the gauge for the rotational variables, where the unphysical degrees of freedom are eliminated already from the Feynman rules, and all the orbital field modes are integrated out. The equations of motion of the spin can be directly obtained via a proper variation of the action, and Hamiltonians may be straightforwardly derived. We implement this effective field theory for spin to derive all spin dependent potentials up to next-to-leading order to quadratic level in spin, namely up to the third post-Newtonian order for rapidly rotating compact objects. In particular, the proper next-to-leading order spin-squared potential and Hamiltonian for generic compact objects are also derived. For the implementations we use the nonrelativistic gravitational field decomposition, which is found here to eliminate higher-loop Feynman diagrams also in spin dependent sectors, and facilitates derivations. This formulation for spin is thus ideal for treatment of higher order spin dependent sectors.
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next to next to leading order post newtonian spin 1 spin 2 hamiltonian for self gravitating binaries
Annalen der Physik, 2011Co-Authors: Johannes Hartung, Jan SteinhoffAbstract:We present the next-to-next-to-leading order post-Newtonian (PN) spin-orbit Hamiltonian for two self-gravitating spinning compact objects. If at least one of the objects is rapidly rotating, then the corresponding interaction is comparable in strength to a 3.5PN effect. The result in the present paper in fact completes the knowledge of the post-Newtonian Hamiltonian for binary spinning black holes up to and including 3.5PN. The Hamiltonian is checked via known results for the test-spin case and via the global Poincare algebra with the center-of-mass vector uniquely determined by an ansatz.
Michele Levi - One of the best experts on this subject based on the ideXlab platform.
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next to next to leading order gravitational spin orbit coupling via the effective field theory for spinning objects in the post newtonian scheme
Journal of Cosmology and Astroparticle Physics, 2016Co-Authors: Michele Levi, Jan SteinhoffAbstract:We implement the effective field theory for gravitating spinning objects in the post-Newtonian scheme at the next-to-next-to-leading order level to derive the gravitational spin-orbit interaction potential at the third and a half post-Newtonian order for rapidly rotating compact objects. From the next-to-next-to-leading order interaction potential, which we obtain here in a Lagrangian form for the first time, we derive straightforwardly the corresponding Hamiltonian. The spin-orbit sector constitutes the most elaborate spin dependent sector at each order, and accordingly we encounter a proliferation of the relevant Feynman diagrams, and a significant increase of the computational complexity. We present in detail the evaluation of the interaction potential, going over all contributing Feynman diagrams. The computation is carried out in terms of the ``nonrelativistic gravitational'' fields, which are advantageous also in spin dependent sectors, together with the various gauge choices included in the effective field theory for gravitating spinning objects, which also optimize the calculation. In addition, we automatize the effective field theory computations, and carry out the automated computations in parallel. Such automated effective field theory computations would be most useful to obtain higher order post-Newtonian corrections. We compare our Hamiltonian to the ADM Hamiltonian, and arrive at a complete agreement between the ADM and effective field theory results. Finally, we provide Hamiltonians in the center of mass frame, and complete gauge invariant relations among the binding energy, angular momentum, and orbital frequency of an inspiralling binary with generic compact spinning components to third and a half post-Newtonian order. The derivation presented here is essential to obtain further higher order post-Newtonian corrections, and to reach the accuracy level required for the successful detection of gravitational radiation.
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next to next to leading order gravitational spin orbit coupling via the effective field theory for spinning objects in the post newtonian scheme
arXiv: General Relativity and Quantum Cosmology, 2015Co-Authors: Michele Levi, Jan SteinhoffAbstract:We implement the effective field theory for gravitating spinning objects in the post-Newtonian scheme at the next-to-next-to-leading order level to derive the gravitational spin-orbit interaction potential at the third and a half post-Newtonian order for rapidly rotating compact objects. From the next-to-next-to-leading order interaction potential, which we obtain here in a Lagrangian form for the first time, we derive straightforwardly the corresponding Hamiltonian. The spin-orbit sector constitutes the most elaborate spin dependent sector at each order, and accordingly we encounter a proliferation of the relevant Feynman diagrams, and a significant increase of the computational complexity. We present the evaluation of the interaction potential, going over contributing Feynman diagrams. The computation is carried out in terms of the nonrelativistic gravitational fields, together with the various gauge choices included in the effective field theory for gravitating spinning objects, which optimize the calculation. In addition, we automatize the effective field theory computations, and carry out the automated computations in parallel. Such automated effective field theory computations would be most useful to obtain higher order post-Newtonian corrections. We compare our Hamiltonian to the ADM Hamiltonian, and arrive at a complete agreement between the ADM and effective field theory results. We provide complete gauge invariant relations among the binding energy, angular momentum, and orbital frequency of an inspiralling binary with generic compact spinning components to third and a half post-Newtonian order. The derivation presented here is essential to obtain further higher order post-Newtonian corrections, and to reach the accuracy level required for the successful detection of gravitational radiation.
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an effective field theory for gravitating spinning objects in the post newtonian scheme
arXiv: General Relativity and Quantum Cosmology, 2015Co-Authors: Michele Levi, Jan SteinhoffAbstract:An effective field theory for gravitating spinning objects in the post-Newtonian approximation is formulated in the context of the binary inspiral problem. We aim at an effective action, where all field modes below the orbital scale are integrated out. We spell out the relevant degrees of freedom, in particular the rotational ones, and the associated symmetries. Building on these symmetries, we introduce the minimal coupling part of the point particle action in terms of gauge rotational variables. We then proceed to construct the spin-induced nonminimal couplings, where we obtain the leading order couplings to all orders in spin for the first time. We specify to a gauge for the rotational variables, where the unphysical degrees of freedom are eliminated already from the Feynman rules, and all the orbital field modes are conveniently integrated out. The equations of motion of spin are then directly obtained via a proper variation of the action, and they take on a simple form. We implement this effective field theory for spin to derive all spin dependent potentials up to next-to-leading order to quadratic level in spin, namely up to the third post-Newtonian order for rapidly rotating compact objects. For the implementations we use the nonrelativistic gravitational field decomposition, which is found here to eliminate higher-loop Feynman diagrams also in spin dependent sectors, and facilitates derivations. Finally, the corresponding Hamiltonians are also straightforwardly obtained from the potentials derived via this formulation. Thus, the formulation is ideal for the treatment of further higher order spin dependent sectors.
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spinning gravitating objects in the effective field theory in the post newtonian scheme
arXiv: General Relativity and Quantum Cosmology, 2015Co-Authors: Michele Levi, Jan SteinhoffAbstract:We introduce a formulation for spinning gravitating objects in the effective field theory in the post-Newtonian scheme in the context of the binary inspiral problem. We aim at an effective action, where all field modes below the orbital scale are integrated out. We spell out the relevant degrees of freedom, in particular the rotational ones, and the associated symmetries. Building on these symmetries, we introduce the minimal coupling part of the point particle action in terms of gauge rotational variables, and construct the spin-induced nonminimal couplings, where we obtain the leading order couplings to all orders in spin. We specify the gauge for the rotational variables, where the unphysical degrees of freedom are eliminated already from the Feynman rules, and all the orbital field modes are integrated out. The equations of motion of the spin can be directly obtained via a proper variation of the action, and Hamiltonians may be straightforwardly derived. We implement this effective field theory for spin to derive all spin dependent potentials up to next-to-leading order to quadratic level in spin, namely up to the third post-Newtonian order for rapidly rotating compact objects. In particular, the proper next-to-leading order spin-squared potential and Hamiltonian for generic compact objects are also derived. For the implementations we use the nonrelativistic gravitational field decomposition, which is found here to eliminate higher-loop Feynman diagrams also in spin dependent sectors, and facilitates derivations. This formulation for spin is thus ideal for treatment of higher order spin dependent sectors.
R Ravi - One of the best experts on this subject based on the ideXlab platform.
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primal dual meets local search approximating mst s with nonuniform degree bounds
Symposium on the Theory of Computing, 2003Co-Authors: Jochen Könemann, R RaviAbstract:We present a new bicriteria approximation algorithm for the degree-bounded minimum-cost spanning tree problem: Given an undirected graph with nonnegative edge weights and degree bounds B v > 1 for all vertices v, find a spanning tree T of minimum total edge-cost such that the maximum degree of each node v in T is at most B v . Our algorithm finds a tree in which the degree of each node v is O(B v + log n) and the total edge-cost is at most a constant times the cost of any tree that obeys all degree constraints.Our previous algorithm[9] with similar guarantees worked only in the case of uniform degree bounds (i.e. B v =B for all vertices v). While the new algorithm is based on ideas from Lagrangean relaxation as is our previous work, it does not rely on computing a solution to a linear program. Instead it uses a repeated application of Kruskal's MST algorithm interleaved with a combinatorial update of approximate Lagrangean node-multipliers maintained by the algorithm. These updates cause subsequent repetitions of the spanning tree algorithm to run for longer and longer times, leading to overall progress and a proof of the performance guarantee.
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a matter of degree improved approximation algorithms for degree bounded minimum spanning trees
SIAM Journal on Computing, 2002Co-Authors: Jochen Könemann, R RaviAbstract:In this paper, we present a new bicriteria approximation algorithm for the degree-bounded minimum spanning tree problem. In this problem, we are given an undirected graph, a nonnegative cost function on the edges, and a positive integer B*, and the goal is to find a minimum-cost spanning tree T with maximum degree at most B*. In an n-node graph, our algorithm finds a spanning tree with maximum degree O(B*+logn) and cost O(optB*), where optB* is the minimum cost of any spanning tree whose maximum degree is at most B*. Our algorithm uses ideas from Lagrangean duality. We show how a set of optimum Lagrangean multipliers yields bounds on both the degree and the cost of the computed solution.
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a polynomial time approximation scheme for minimum routing cost spanning trees
SIAM Journal on Computing, 1999Co-Authors: Giuseppe Lancia, R Ravi, Vineet Bafna, Kunmao Chao, Chuan Yi TangAbstract:Given an undirected graph with nonnegative costs on the edges, the routing cost of any of its spanning trees is the sum over all pairs of vertices of the cost of the path between the pair in the tree. Finding a spanning tree of minimum routing cost is NP-hard, even when the costs obey the triangle inequality. We show that the general case is in fact reducible to the metric case and present a polynomial-time approximation scheme valid for both versions of the problem. In particular, we show how to build a spanning tree of an n-vertex weighted graph with routing cost at most $(1+\epsilon)$ of the minimum in time $O(n^{O({\frac{1}{\epsilon}}% )})$. Besides the obvious connection to network design, trees with small routing cost also find application in the construction of good multiple sequence alignments in computational biology. The communication cost spanning tree problem is a generalization of the minimum routing cost tree problem where the routing costs of different pairs are weighted by different requirement amounts. We observe that a randomized O(log n log log n)-approximation for this problem follows directly from a recent result of Bartal, where n is the number of nodes in a metric graph. This also yields the same approximation for the generalized sum-of-pairs alignment problem in computational biology.
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a polynomial time approximation scheme for minimum routing cost spanning trees
Symposium on Discrete Algorithms, 1998Co-Authors: Giuseppe Lancia, R Ravi, Vineet Bafna, Kunmao Chao, Chuan Yi TangAbstract:Given an undirected graph with nonnegative costs on the edges, the routing cost of any of its spanning trees is the sum over all pairs of vertices of the cost of the path between the pair in the tree. Finding a spanning tree of minimum routing cost is NP-hard, even when the costs obey the triangle inequality. We show that the general case is in fact reducible to the metric case and present a polynomial-time approximation scheme valid for both versions of the problem. In particular, we show how to build a spanning tree of an n-vertex weighted graph with routing cost at most (1 +) of the minimum in time O(n O( 1 ) ). Besides the obvious connection to network design, trees with small routing cost also nd application in the construction of good multiple sequence alignments in computational biology. The communication cost spanning tree problem is a generalization of the minimum routing cost tree problem where the routing costs of dierent pairs are weighted by dierent requirement amounts. We observe that a randomized O(logn log logn)-approximation for this problem follows directly from a recent result of Bartal, where n is the number of nodes in a metric graph. This also yields the same approximation for the generalized sum-of-pairs alignment problem in computational biology.
Serge Mora - One of the best experts on this subject based on the ideXlab platform.
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Buckling of a spinning elastic cylinder: linear, weakly nonlinear and post-buckling analyses
Proceedings of the Royal Society A: Mathematical Physical and Engineering Sciences, 2018Co-Authors: Franck Richard, Aditi Chakrabarti, Basile Audoly, Yves Pomeau, Serge MoraAbstract:An elastic cylinder spinning about a rigid axis buckles beyond a critical angular velocity, by an instability driven by the centrifugal force. This instability and the competition between the different buckling modes are investigated using analytical calculations in the linear and weakly nonlinear regimes, complemented by numerical simulations in the fully post-buckled regime. The weakly nonlinear analysis is carried out for a generic incompressible hyperelastic material. The key role played by the quadratic term in the expansion of the strain energy density is pointed out: this term has a strong effect on both the nature of the bifurcation, which can switch from supercritical to subcritical, and on the buckling amplitude. Given an arbitrary hyperelastic material, an equivalent shear modulus is proposed, allowing the main features of the instability to be captured by an equivalent neo-Hookean model.