Constructive cooperative coevolution for large-scale global optimisation

This paper presents the Constructive Cooperative Coevolutionary (\(\mathrm {C}^3\)) algorithm, applied to continuous large-scale global optimisation problems. The novelty of \(\mathrm {C}^3\) is that it utilises a multi-start architecture and incorporates the Cooperative Coevolutionary algorithm. The considered optimisation problem is decomposed into subproblems. An embedded optimisation algorithm optimises the subproblems separately while exchanging information to co-adapt the solutions for the subproblems. Further, \(\mathrm {C}^3\) includes a novel constructive heuristic that generates different feasible solutions for the entire problem and thereby expedites the search. In this work, two different versions of \(\mathrm {C}^3\) are evaluated on high-dimensional benchmark problems, including the CEC’2013 test suite for large-scale global optimisation. \(\mathrm {C}^3\) is compared with several state-of-the-art algorithms, which shows that \(\mathrm {C}^3\) is among the most competitive algorithms. \(\mathrm {C}^3\) outperforms the other algorithms for most partially separable functions and overlapping functions. This shows that \(\mathrm {C}^3\) is an effective algorithm for large-scale global optimisation. This paper demonstrates the enhanced performance by using constructive heuristics for generating initial feasible solutions for Cooperative Coevolutionary algorithms in a multi-start framework.     

Reduced Functions, Gradients and Hessians from Fixed-Point Iterations for State Equations

In design optimization and parameter identification, the objective, or response function(s) are typically linked to the actually independent variables through equality constraints, which we will refer to as state equations. Our key assumption is that it is impossible to form and factor the corresponding constraint Jacobian, but one has instead some fixed-point algorithm for computing a feasible state, given any reasonable value of the independent variables. Assuming that this iteration is eventually contractive, we will show how reduced gradients (Jacobians) and Hessians (in other words, the total derivatives) of the response(s) with respect to the independent variables can be obtained via algorithmic, or automatic, differentiation (AD). In our approach the actual application of the so-called reverse, or adjoint differentiation mode is kept local to each iteration step. Consequently, the memory requirement is typically not unduly enlarged. The resulting approximating Lagrange multipliers are used to compute estimates of the reduced function values that can be shown to converge twice as fast as the underlying state space iteration. By a combination with the forward mode of AD, one can also obtain extra-accurate directional derivatives of the reduced functions as well as feasible state space directions and the corresponding reduced or projected Hessians of the Lagrangian. Our approach is verified by test calculations on an aircraft wing with two responses, namely, the lift and drag coefficient, and two variables, namely, the angle of attack and the Mach number. The state is a 2-dimensional flow field defined as solution of the discretized Euler equation under transonic conditions.     

Transient nutation and molecular echoes in microwave double resonance experiments

Transient phenomena occurring in time resolved microwave-microwave double resonance experiments when the pump power is switched on and off have been investigated both theoretically and experimentally. Special attention has been paid to the case when both fields are saturating and exactly resonant. A calculation using the evolution operator formalism has been carried out to explain the experimental results. Transient nutations similar to those observed by the Stark modulation method have been observed and theoretically explained. A new phenomenon, the driven induction decay, has also been observed when the pump power is switched on. Moreover, double resonance photon echoes have also been exhibited. The application of these methods to relaxation studies is discussed.     

Optoacoustic investigation of the mechanisms in the infrared optogalvanic effect

Simultaneous observations of the optogalvanic and optoacoustic effects were performed in CO₂, NH₃ and SF₆ discharges under irradiation by resonant infrared 10 μm laser radiation. The dependence of the galvanic and acoustic signals on the discharge current, and their time evolution following a switch of the laser radiation were investigated. The observations proved that the infrared optogalvanic effect occurs through two different mechanisms, a gas kinetic temperature dependence of the discharge parameters and a modification of the pion production through the vibrational molecular excitation.