Branch predictor

In computer architecture, a branch predictor is a digital circuit that tries to guess which way a branch (e.g., an if–then–else structure) will go before this is known definitively. The purpose of the branch predictor is to improve the flow in the instruction pipeline. Branch predictors play a critical role in achieving high performance in many modern pipelined microprocessor architectures. Two-way branching is usually implemented with a conditional jump instruction. A conditional jump can either be "taken" and jump to a different place in program memory, or it can be "not taken" and continue execution immediately after the conditional jump. It is not known for certain whether a conditional jump will be taken or not taken until the condition has been calculated and the conditional jump has passed the execution stage in the instruction pipeline (see fig. 1). Without branch prediction, the processor would have to wait until the conditional jump instruction has passed the execute st

Théorie de bifurcation et de stabilité pour une équation de Schrödinger avec une non-linéarité compacte

François Samer Genoud

The nonlinear Schrödinger equation i∂tw + Δw +V(x)|w|p-1w = 0 w = w(t,x) : Ι × RN → C, N ≥ 2, (1) is studied, with p > 1, V : RN \ {0} → R and Ι ⊂ R an interval. The coefficient V is subject to various hypotheses. In particular, it is always assumed that V (x) → 0 as |x| → ∞. Situations where V is unbounded at the origin are considered. A special attention is paid to the radial case. Seeking solutions of (1) as standing waves w(t,x) = eiλtu(x) leads naturally to the semilinear elliptic equation Δu - λu + V(x)|u|p-1u = 0 u : RN → R, N ≥ 2. (2) The main goals of the thesis are to establish existence and bifurcation results for (2), to discuss the orbital stability of the standing waves of (1) corresponding to the solutions found in (A). First, in Chapter 1, in the case where V is radial, a variational approach shows the existence of ground states for (2). A non-degeneracy property of these solutions is proved, which plays a crucial role in the continuation arguments of Chapter 2. The first part of Chapter 2 establishes local existence and bifurcation results for (2), without any symmetry assumption on V . Under certain hypotheses on the power p and the coefficient V , two branches of solutions are obtained, in a neighborhood of λ = 0 and in a neighborhood of λ = +∞. The branches are of class Cr if V ∈ Cr(RN \ {0},R), for r = 0, 1. These independent results are proved by requiring respectively that lim|x|→∞ V (x)|x|b = B > 0 with b ∈ (0, 2) and that limx→0 V (x)|x|a = A > 0 with a ∈ (0, 2). The asymptotic behaviour along the branches is discussed in detail and depends on the value of p. The second part of Chapter 2 proves the existence of a global branch of solutions of (2), in the case where V is radial. Under appropriate hypotheses, in particular if a ∈ (0, b], the global branch "sticks together" the two local branches obtained in the first part. Chapter 3 is concerned with the orbital stability of the standing waves of (1) corresponding to the solutions of (2) found in the first part of Chapter 2. It is explained in detail how to apply the general theory of orbital stability to (1). Local stability/instability results are proved, in a neighborhood of λ = 0 and in a neighborhood of λ = +∞.

EPFL2008

Existence And Stability Of High Frequency Standing Waves For A Nonlinear Schrodinger Equation

François Samer Genoud

This article is concerned with the existence and orbital stability of standing waves for a nonlinear Schrodinger equation (NLS) with a nonautonomous nonlinearity. It continues and concludes the series of papers [6, 7, 8]. In [6], the authors make use of a continuation argument to establish the existence in R x H-1(R-N) of a smooth local branch of solutions to the stationary elliptic problem associated with (NLS) and hence the existence of standing wave solutions of (NLS) with small frequencies. Complementary conditions on the nonlinearity are found, under which either stability of the standing waves and bifurcation of the branch of solutions from the point (0, 0) is an element of R x H-1 (R-N) occur, or instability and asymptotic bifurcation occur. The main hypotheses in [6] concern the behaviour of the nonlinearity with respect to the space variable at infinity. The paper [7] extends the results of [6] to (NLS) with more general nonlinearities. In [8], the global continuation of the local branch obtained in [6] is proved under additional hypotheses on the nonlinearity. In particular, spherical symmetry with respect to the space variable is assumed. The aim of the present work is to prove the existence and discuss the orbital stability of standing waves with high frequencies, independently of the results obtained in [6] and [8]. The main hypotheses now concern the behaviour of the nonlinearity with respect to the space variable around the origin. The methods are the same in spirit as that of [6] and permit to discuss the asymptotic behaviour of the global branch of solutions obtained in [8].

2009

Théorie de bifurcation et de stabilité pour une équation de Schrödinger avec une non-linéarité compacte

François Samer Genoud

EPFL2008

Prediction based on pairwise likelihood

Théorie de bifurcation et de stabilité pour une équation de Schrödinger avec une non-linéarité compacte

Existence And Stability Of High Frequency Standing Waves For A Nonlinear Schrodinger Equation

Théorie de bifurcation et de stabilité pour une équation de Schrödinger avec une non-linéarité compacte

Prediction based on pairwise likelihood

Existence And Stability Of High Frequency Standing Waves For A Nonlinear Schrodinger Equation