On the cost–effectiveness of PRAMs

We introduce a formalism which allows to treat computer architecture as a formal optimization problem. We apply this to the design of shared memory parallel machines. While present parallel computers of this type only support the programming model of a shared memory but often process simultaneous access by several processors to the shared memory sequentially, theoretical computer science offers solutions for this problem that are provably fast and asymptotically optimal. But the constants in these constructions seemed to be too large to let them be competitive. We modify these constructions under engineering aspects and improve the price/performance ratio by roughly a factor of 6. The resulting machine has surprisingly good price/performance ratio even if compared with distributed memory machines. For almost all access patterns of all processors into the shared memory, access is as fast as the access of only a single processor. Received: 29 June 1993 / 22 June 1999     

On the computation of Bernstein–Sato ideals

In this paper we compare the approach of Briançon and Maisonobe for computing Bernstein–Sato ideals—based on computations in a Poincaré–Birkhoff–Witt algebra—with the readily available method of Oaku and Takayama. We show that it can deal with interesting examples that have proved intractable so far.     

On the size of Boyer–Moore automata

In this work we study the size of Boyer–Moore automata introduced in Knuth, Morris & Pratt’s famous paper on pattern matching. We experimentally show that a finite class of binary patterns produce very large Boyer–Moore automata, and find one particular case which we conjecture, generates automata of size Ω(m⁶)$\Omega \left(m^6\right)$. Further experimental results suggest that the maximal size could be a polynomial of O(m⁷)$O\left(m^7\right)$, or even an exponential O(2^0.4m)$O\left(2^{0.4m}\right)$, where m$m$ is the length of the pattern.     

On Total Unimodularity of Edge–Edge Adjacency Matrices

We consider total unimodularity for edge–edge adjacency matrices that represent adjacency relations between pairs of edges in a graph. These matrices appear in integer programming formulations of the minimum maximal matching problem, the edge dominating set problem, and so on. We investigate the problem of characterizing graphs that have totally unimodular edge–edge adjacency matrices, and give a necessary and sufficient condition for characterization. This condition is the first characterization for total unimodularity of edge–edge adjacency matrices.     

On some generalizations of the Thue–Morse morphism

In 1912, the Norwegian mathematician Axel Thue was the first to describe an overlap-free binary infinite word. This word was generated by a morphism which is called, since the works of Morse, the Thue–Morse morphism. Here, we present two generalizations of the Thue–Morse morphism in the case of alphabets with more than two letters. The extension of the characteristic properties of the word of Thue to the words generated by these morphisms is considered. One of these generalizations corresponds to the construction of Prouhet and a link with the Arshon words is given. In particular, we prove that if n is an even number then the n-letter Arshon word is generated by morphism.     

On the LAI of mixed soils–forests regions

In homogeneous forest textures, it has been recently confirmed experimentally that, for sufficiently large ground surfaces, the Leaf Area Index (LAI) has weak variations with respect to ground surface variations. This allows computing the LAI of mixed pixels on regions composed of forests and soils, with the use of the Perpendicular Vegetation Index (PVI). In the present paper, we study the accuracy of the method with experimental data.     

On the numerical solution of differential equations of Lane–Emden type

In this paper, a numerical method which produces an approximate polynomial solution is presented for solving Lane–Emden equations as singular initial value problems. Firstly, we use an integral operator (Yousefi (2006) [4]) and convert Lane–Emden equations into integral equations. Then, we convert the acquired integral equation into a power series. Finally, transforming the power series into Padé series form, we obtain an approximate polynomial of arbitrary order for solving Lane–Emden equations. The advantages of using the proposed method are presented. Then, an efficient error estimation for the proposed method is also introduced and finally some experiments and their numerical solutions are given; and comparing between the numerical results obtained from the other methods, we show the high accuracy and efficiency of the proposed method.     

On the stability of the secular evolution of the planar Sun–Jupiter–Saturn–Uranus system

We investigate the long time stability of the Sun–Jupiter–Saturn–Uranus system by considering the planar, secular model. Our method may be considered as an extension of Lagrange’s theory for the secular motions. Indeed, concerning the planetary orbital revolutions, we improve the classical circular approximation by replacing it with a torus which is invariant up to order two in the masses; therefore, we investigate the stability of the elliptic equilibrium point of the secular system for small values of the eccentricities. For the initial data corresponding to a real set of astronomical observations, we find an estimated stability time of 10⁷ years, which is not extremely smaller than the lifetime of the Solar System (∼5 Gyr).     

Choosing starting values for certain Newton–Raphson iterations

We aim at finding the best possible seed values when computing a^1/p$a^{1/p}$ using the Newton–Raphson iteration in a given interval. A natural choice of the seed value would be the one that best approximates the expected result. It turns out that in most cases, the best seed value can be quite far from this natural choice. When we evaluate a monotone function f(a)$f(a)$ in the interval [_amin,_amax]$[a_{\min },a_{\max }]$, by building the sequence _xn$x_n$ defined by the Newton–Raphson iteration, the natural choice consists in choosing _x0$x_0$ equal to the arithmetic mean of the endpoint values. This minimizes the maximum possible distance between _x0$x_0$ and f(a)$f(a)$. And yet, if we perform n$n$ iterations, what matters is to minimize the maximum possible distance between _xn$x_n$ and f(a)$f(a)$. In several examples, the value of the best starting point varies rather significantly with the number of iterations.     

On the Stability of Continuous–Discontinuous Galerkin Methods for Advection–Diffusion–Reaction Problems

We consider a finite element method which couples the continuous Galerkin method away from internal and boundary layers with a discontinuous Galerkin method in the vicinity of layers. We prove that this consistent method is stable in the streamline diffusion norm if the convection field flows non-characteristically from the region of the continuous Galerkin to the region of the discontinuous Galerkin method. The stability properties of the coupled method are illustrated with a numerical experiment.     

On human–machine relations

Cognition, Technology & Work - This paper presents an approach to human–machine interactions based on the concept of teamwork and the psychological theory of object relations. We envision...     

On the first-order estimation of multipliers from Kuhn–Tucker systems

The minimization of a nonlinear function with linear and nonlinear constraints and simple bounds can be performed by minimizing an augmented Lagrangian function that includes only the nonlinear constraints subject to the linear constraints and simple bounds. It is then necessary to estimate the multipliers of the nonlinear constraints and variable reduction techniques can be used to carry out the successive minimizations. The viability of estimating the multipliers of the nonlinear constraints from the Kuhn–Tucker system is analyzed and an acceptability test on the residual of the estimation is put forward. The computational performance of the procedure is compared with that of the inexpensive Hestenes–Powell multiplier update.Scope and purposeIt is possible to minimize a nonlinear function with linear and nonlinear constraints and simple bounds through the successive minimization of an augmented Lagrangian function including only the nonlinear constraints subject to the linear constraints and simple bounds. This method is particularly interesting when the linear constraints are flow conservation equations, as there are efficient techniques for solving nonlinear network problems. Regarding the successive estimation of the multipliers of the nonlinear constraints there is some doubt as to whether using the Kuhn–Tucker system could improve upon the inexpensive Hestenes–Powell update, especially considering that the Kuhn–Tucker system with partial augmented Lagrangians may not always lead to an acceptable multiplier estimation. Clarifying the computational efficiency of the multiplier update when there are linear or nonlinear side constraints is also a necessary previous step regarding the comparison between partial augmented Lagrangian techniques and either primal partitioning techniques for linear side constraints or projected Lagrangian methods in the case of nonlinear side constraints.     

On linear stability of predictor–corrector algorithms for fractional differential equations

This paper deals with the numerical approximation of differential equations of fractional order by means of predictor–corrector algorithms. A linear stability analysis is performed and the stability regions of different methods are compared. Furthermore the effects on stability of multiple corrector iterations are verified.     

On the well-posedness of a spectral fractional forward–backward pseudo-parabolic equation

We prove existence, uniqueness and stability of solution of a forward–backward pseudo-parabolic equation with spectral fractional Laplacian. Then we define and prove existence of Young measure valued solution for fractional forward–backward problem by the vanishing viscosity method.     

On Convergence of the Arrow–Hurwicz Method for Saddle Point Problems

Journal of Mathematical Imaging and Vision - The Arrow–Hurwicz method is an inexact version of the Uzawa method; it has been widely applied to solve various saddle point problems in different...     

On two versions of the Loomis–Sikorski Theorem for algebraic structures

We present two versions of the Loomis–Sikorski Theorem, one for monotone σ-complete generalized pseudo effect algebras with strong unit satisfying a kind of the Riesz decomposition property. The second one is for Dedekind σ-complete positive pseudo Vitali spaces with strong unit. For any case we can find an appropriate system of nonnegative bounded functions forming an algebra of the given type with the operations defined by points that maps epimorphically onto the algebra. The paper has been supported by the Center of Excellence SAS—Physics of Information—I/2/2005, the grant VEGA No. 2/6088/26 SAV, the Slovak Research and Development Agency under the contract No. APVV-0071-06, Slovak-Italian Project No. 15:“Algebraic and logical systems of soft computing”, and MURST, project “Analisi Reale”.