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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 54 (1992), S. 307-333 
    ISSN: 1436-4646
    Keywords: Value convergence ; reachability ; solution set convergence ; tie-breaking ; stopping rule ; infinite horizon optimization ; production planning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We consider the problem of approximating an optimal solution to a separable, doubly infinite mathematical program (P) with lower staircase structure by solutions to the programs (P(N)) obtained by truncating after the firstN variables andN constraints of (P). Viewing the surplus vector variable associated with theNth constraint as a state, and assuming that all feasible states are eventually reachable from any feasible state, we show that the efficient set of all solutions optimal to all possible feasible surplus states for (P(N)) converges to the set of optimal solutions to (P). A tie-breaking algorithm which selects a nearest-point efficient solution for (P(N)) is shown (for convex programs) to converge to an optimal solution to (P). A stopping rule is provided for discovering a value ofN sufficiently large to guarantee any prespecified level of accuracy. The theory is illustrated by an application to production planning.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 53 (1992), S. 323-338 
    ISSN: 1436-4646
    Keywords: Random search ; Monte Carlo optimization ; global optimization ; complexity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract Pure adaptive seach iteratively constructs a sequence of interior points uniformly distributed within the corresponding sequence of nested improving regions of the feasible space. That is, at any iteration, the next point in the sequence is uniformly distributed over the region of feasible space containing all points that are strictly superior in value to the previous points in the sequence. The complexity of this algorithm is measured by the expected number of iterations required to achieve a given accuracy of solution. We show that for global mathematical programs satisfying the Lipschitz condition, its complexity increases at mostlinearly in the dimension of the problem.
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  • 3
    Electronic Resource
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    Springer
    Mathematical programming 59 (1993), S. 215-229 
    ISSN: 1436-4646
    Keywords: Dynamic programming ; deterministic and Markov ; infinite state: infinite stage problems ; programming ; infinite dimensional: infinite horizon optimization ; shortest paths ; infinite networks
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We present necessary and sufficient conditions for discrete infinite horizon optimization problems with unique solutions to be solvable. These problems can be equivalently viewed as the task of finding a shortest path in an infinite directed network. We provide general forward algorithms with stopping rules for their solution. The key condition required is that of weak reachability, which roughly requires that for any sequence of nodes or states, it must be possible from optimal states to reach states close in cost to states along this sequence. Moreover the costs to reach these states must converge to zero. Applications are considered in optimal search, undiscounted Markov decision processes, and deterministic infinite horizon optimization.
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  • 4
    ISSN: 1572-8889
    Keywords: Belostomatidae ; giant water bugs ; paternal care ; eggs ; reproduction ; behavior ; brooding ; evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Males of the giant water bug Lethocerus medius(Guerin) typify their monobasic subfamily, the Lethocerinae, in that they do not brood eggs attached to their backs as do males of all members of the subfamily Belostomatinae. Exclusive male parental investment as expressed in the Belostomatinae is extremely rare behavior among animals, and evolution of the trait is obscure. Lethocerus mediusmales apparently remain with their mates through oviposition and are consistently found in attendance of eggs after the female has departed. This behavior may enhance paternity assurance at no cost in opportunity for polygyny. Two double clutches of eggs were found, from which we infer the potential for polygynous matings and shared parental investment. Male L. mediusbrood attended egg clutches above the surface of the water, where they may moisten them, shade them, and defend them against predation. Egg attendance/brooding by L. mediusand other Lethocerusspecies may represent a plesiomorphic state from which paternal back- brooding evolved in the Belostomatinae.
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  • 5
    Electronic Resource
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    Springer
    Mathematical programming 24 (1982), S. 39-54 
    ISSN: 1436-4646
    Keywords: Random Polytopes ; Linear Programming ; Problem Generation ; Aggregate Polytope Properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract The definition of random polytope adopted in this paper restricts consideration to those probability measures satisfying two properties. First, the measure must induce an absolutely continuous distribution over the positions of the bounding hyperplanes of the random polytope; and second, it must result in every point in the space being equally as likely as any other point of lying within the random polytope. An efficient Monte Carlo method for their computer generation is presented together with analytical formulas characterizing their aggregate properties. In particular, it is shown that the expected number of extreme points for such random polytopes increases monotonically in the number of constraints to the limiting case of a polytope topologically equivalent to a hypercube. The implied upper bound of 2 n wheren is the dimensionality of the space is significantly less than McMullen's attainable bound on the maximal number of vertices even for a moderate number of constraints.
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  • 6
    Electronic Resource
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    Springer
    Mathematical programming 35 (1986), S. 129-134 
    ISSN: 1436-4646
    Keywords: Random linear program ; random polytope ; extreme points
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract There has been increasing attention recently on average case algorithmic performance measures since worst case measures can be qualitatively quite different. An important characteristic of a linear program, relating to Simplex Method performance, is the number of vertices of the feasible region. We show 2 n to be an upper bound on the mean number of extreme points of a randomly generated feasible region with arbitrary probability distributions on the constraint matrix and right hand side vector. The only assumption made is that inequality directions are chosen independently in accordance with a series of independent fair coin tosses.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 43 (1989), S. 317-328 
    ISSN: 1436-4646
    Keywords: Random search ; Monte Carlo optimization ; convex programming
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract Pure adaptive search constructs a sequence of points uniformly distributed within a corresponding sequence of nested regions of the feasible space. At any stage, the next point in the sequence is chosen uniformly distributed over the region of feasible space containing all points that are equal or superior in value to the previous points in the sequence. We show that for convex programs the number of iterations required to achieve a given accuracy of solution increases at most linearly in the dimension of the problem. This compares to exponential growth in iterations required for pure random search.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 53 (1992), S. 79-97 
    ISSN: 1436-4646
    Keywords: Infinite dimensional linear program ; duality ; infinite horizon optimization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We consider the class of linear programs with infinitely many variables and constraints having the property that every constraint contains at most finitely many variables while every variable appears in at most finitely many constraints. Examples include production planning and equipment replacement over an infinite horizon. We form the natural dual linear programming problem and prove strong duality under a transversality condition that dual prices are asymptotically zero. That is, we show, under this transversality condition, that optimal solutions are attained in both primal and dual problems and their optimal values are equal. The transversality condition, and hence strong duality, is established for an infinite horizon production planning problem.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Boundary layer meteorology 3 (1973), S. 385-391 
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Harmonic analysis of longshore and onshore components of surface winds over an upwelling area off the coast of Peru shows regular, nearly sinusoidal, diurnal variations in both velocity components. Spectral analysis of wind speed also indicates strong diurnal variations in kinetic energy. The data are compatible with a recent model of coastal winds proposed by Lettau and Lettau.
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  • 10
    Electronic Resource
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    Springer
    Ocean dynamics 33 (1980), S. 223-235 
    ISSN: 1616-7228
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Description / Table of Contents: Zusammenfassung Es werden einige Aspekte der halbtägigen Gezeitenströme auf dem Schelf und am Kontinentalabhang vor Mauretanien beschrieben. Die Grundlage hierzu bilden Strömungsmeßergebnisse des küstennahen Auftriebsexperiments JOINT-I (Februar bis April 1974). Die halbtägigen Gezeiten sind die auffälligsten kurzperiodischen Schwankungen auf dem mauretanischen Schelf. Die Geschwindigkeiten der halbtägigen Gezeitenströme schwanken zwischen 1 cm s−1 und 10 cm s−1. Ihre mittlere Geschwindigkeit von 5 cm s−1 entspricht 15% bis 25% der lokalen Reststromgeschwindigkeit (nach Eliminierung der Gezeitenströme). Der größte Beitrag zu den halbtägigen Gezeitenströmen stammt von der M2-Tide. Die mittlere Strömungsamplitude mit genau 12stündiger Periode (S2) ist etwa halb so groß wie die M2-Amplitude. Das Signal der 12stündigen Gezeitenströme wird durch den nicht zu trennenden Einfluß schwacher Strömungen infolge halbtägiger Windschwankungen verfälscht. Im täglichen Frequenzband überlagern sich aufgrund der ausgeprägten Land-See-Brise ebenfalls periodische Strömungen den ganztägigen Gezeitenströmen. Im Mittel sind die halbtägigen Gezeiten über dem Schelf barotrop. Über dem Kontinentalabhang tragen dagegen interne Gezeiten erheblich zur Verstärkung der Gezeitenenergie bei. Die quer zum Kontinentalabhang beobachteten markanten Phasendifferenzen der halbtägigen Gezeitenströme sind zum großen Teil auf die Wechselwirkung der barotropen und baroklinen Gezeiten zurückzuführen. Während die halbtägigen Gezeitenströme auf dem Schelf gegen den Uhrzeigersinn drehen, rotieren sie 50 km seewärts vom Schelfrand im Uhrzeigersinn.
    Abstract: Résumé Les mesures de courant obtenues lors de l'étude expérimentale JOINT-I (Février–Avril 1974) de l'upwelling côtier sont utilisées pour décrire certains aspects des courants de marée semi-diurnes sur le plateau et en travers du talus continental au large de la Mauritanie. Sur le plateau, les marées semi-diurnes représentent les fluctuations dominantes de période courte. Les vitesses de courant semi-diurnes vont de 1 à 10 cm s−1. Leur vitesses moyennes d'environ 5 cm s−1 atteignent 15% à 25% des vitesses du courant résiduel. L'onde de marée M2 apporte la contribution principale dans les courants semidiurnes. L'amplitude moyenne des courants à la période de marée S2 est à peu près la moitié de celle de M2. L'indication des courants de marée de période de 12.00 heures (S2) est probablement faussée par de faibles variations semi-diurnes du vent. Dans la bande des fréquences diurnes les variations quotidiennes de la brise terre-mer interfèrent avec les courants de marée. En moyenne, les marées semi-diurnes côtières apparaissent barotropiques. Audessus du talus continental, les marées barocliniques apportent une contribution significative aux courants de marée et renforcent l'énergie de marée. Les interactions des marées barotropiques et barocliniques contribuent aussi aux différences de phase marquées des courants semi-diurnes observables en travers du talus continental. Alors que les courants semi-diurnes tournent en sens contraire des aiguilles d'une montre sur le plateau, ils tournent dans le sens des aiguilles à 50 km au large du rebord du plateau.
    Notes: Summary Current meter measurements obtained during the coastal upwelling experiment JOINT-I (Feb. to April 1974) are used to describe some aspects of the semi-diurnal tidal currents on the shelf and across the continental slope off Mauritania. On the shelf the semi-diurnal tides represent the dominant short-period fluctuations. Semi-diurnal current speeds range between 1 and 10 cm s−1. The mean speeds of about 5 cm s−1 are 15% to 25% of the residual current speeds. The main contribution to the semi-diurnal currents comes from the M2 tide. The mean amplitude of the currents at the period of the S2 tide is about half as large as the amplitude due to the M2. The signal of tidal currents at the period of 12.00 hours (S2) is probably biased by the influence of weak semi-diurnal wind variations. At the diurnal frequency band the daily wind fluctuations of the land-sea-breeze interferes with the tidal currents. When averaged over time, the semi-diurnal tides inshore appear barotropic. Over the continental slope baroclinic tides contribute significantly to the tidal currents and enhance the tidal energy there. The interactions of barotropic and baroclinic tides also contribute to the observed marked phase differences of the semi-diurnal currents across the continental slope. Whereas the semi-diurnal currents rotate counter-clockwise on the shelf they rotate clockwise 50 km offshore the shelf break.
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