Injecting External Solutions Into CMA-ES

This report considers how to inject external candidate solutions into the CMA-ES algorithm. The injected solutions might stem from a gradient or a Newton step, a surrogate model optimizer or any other oracle or search mechanism. They can also be the result of a repair mechanism, for example to render infeasible solutions feasible. Only small modifications to the CMA-ES are necessary to turn injection into a reliable and effective method: too long steps need to be tightly renormalized. The main objective of this report is to reveal this simple mechanism. Depending on the source of the injected solutions, interesting variants of CMA-ES arise. When the best-ever solution is always (re-)injected, an elitist variant of CMA-ES with weighted multi-recombination arises. When \emph{all} solutions are injected from an \emph{external} source, the resulting algorithm might be viewed as \emph{adaptive encoding} with step-size control. In first experiments, injected solutions of very good quality lead to a convergence speed twice as fast as on the (simple) sphere function without injection. This means that we observe an impressive speed-up on otherwise difficult to solve functions. Single bad injected solutions on the other hand do no significant harm.Comment: No. RR-7748 (2011

The CMA Evolution Strategy: A Tutorial

This tutorial introduces the CMA Evolution Strategy (ES), where CMA stands for Covariance Matrix Adaptation. The CMA-ES is a stochastic, or randomized, method for real-parameter (continuous domain) optimization of non-linear, non-convex functions. We try to motivate and derive the algorithm from intuitive concepts and from requirements of non-linear, non-convex search in continuous domain.Comment: ArXiv e-prints, arXiv:1604.xxxx

Biased Multiobjective Optimization and Decomposition Algorithm

The bias feature is a major factor that makes a multiobjective optimization problem (MOP) difficult for multiobjective evolutionary algorithms (MOEAs). To deal with this problem feature, an algorithm should carefully balance between exploration and exploitation. The decomposition-based MOEA decomposes an MOP into a number of single objective subproblems and solves them in a collaborative manner. Single objective optimizers can be easily used in this algorithm framework. Covariance matrix adaptation evolution strategy (CMA-ES) has proven to be able to strike good balance between the exploration and the exploitation of search space. This paper proposes a scheme to use both differential evolution (DE) and covariance matrix adaptation in the MOEA based on decomposition. In this scheme, single objective optimization problems are clustered into several groups. To reduce the computational overhead, only one subproblem from each group is selected to optimize by CMA-ES while other subproblems are optimized by DE. When an evolution strategy procedure meets some stopping criteria, it will be reinitialized and used for solving another subproblem in the same group. A set of new multiobjective test problems with bias features are constructed in this paper. Extensive experimental studies show that our proposed algorithm is suitable for dealing with problems with biases

Populations of spiking neurons for reservoir computing : closed loop control of a compliant quadruped

Compliant robots can be more versatile than traditional robots, but their control is more complex. The dynamics of compliant bodies can however be turned into an advantage using the physical reservoir computing frame- work. By feeding sensor signals to the reservoir and extracting motor signals from the reservoir, closed loop robot control is possible. Here, we present a novel framework for implementing central pattern generators with spik- ing neural networks to obtain closed loop robot control. Using the FORCE learning paradigm, we train a reservoir of spiking neuron populations to act as a central pattern generator. We demonstrate the learning of predefined gait patterns, speed control and gait transition on a simulated model of a compliant quadrupedal robot

In vivo monitoring of human intestinal ischaemia: An on-line rapid sampling microdialysis biosensor system

The primary aim of this thesis was to monitor in vivo intestinal ischemia using rapid sampling on-line microdialysis. A new variant of a clinical assay system was developed for use in gastrointestinal surgery. The assay could process on-line microdialysis samples for glucose and lactate concentrations at 30 seconds intervals in the concentration range of 25 μM to 30 mM. Intramural human bowel ischaemia was monitored intra-operatively in a clinical collaboration with Prof. Darzi and Prof. Hanna in St. Maryʼs Hospital, London using a microdialysis probe implantation technique devised by Mr. Samer Deeba. Dialysate levels stabilised within 10-15 minutes following implantation of the CMA 62 microdialysis probe. Clipping of arteries feeding the gastrointestinal tissue to be resected, did not lead to an immediate change in dialysate levels, but a fall in glucose and rise in lactate delayed by 17 ± 2 minutes, n=9. This suggests an additional pool of glucose availability in the bowel, and indicates a possible therapeutic window during bowel surgery. Parallel experimental work was carried out in swine model in the surgical labs of the healthcare company Tyco (Covidien) in Paris. Rapid sampling microdialysis was used to examine the effect of total ischaemia on an anastomosis site. The anastomotic site was devascularised by clamping the mesentery of both sides. Here the tissue reacted to ischaemia immediately, 5 minutes following clamping of feeding artery, compared with a healthy human bowel, suggesting that the additional glucose pool was unavailable in this situation. Physiological variable effects were studied to investigate further any difference with respect to the human in pig bowel physiology, which were not found. The no-net-flux method of in vivo recovery was used to determine the extracellular levels of glucose (0.47 ± 0.05 mM) in the intramural pig bowel. These were substantially lower than blood glucose values, representing a 10% of plasma levels and suggest a difference with human bowel. Finally, 7 patients were monitored after abdominal aortic aneurism repair surgery, for up to 2 days in the intensive care unit, to detect the possible on-set of ischaemia as a complication of inferior mesenteric artery occlusion. Basal microdialysis levels at 3.98 ± 0.75 mM for glucose and 1.38 ± 0.20 mM for lactate agreed well with those measured acutely during surgery, and were not sensitive to changes in plasma values. The lactate/glucose ratio between 1-2 days post-implantation was typically between 0.5-1.0 again similar to the ratio found intra-operatively. This validates the use of microdialysis intra-operatively and confirms the importance of this ratio. An in vivo calibration was performed in one patient with the variable flow rate method providing extracellular levels for glucose (5.8 ± 0.4 mM) and lactate (3.3 ± 0.2 mM) in intramural human bowel. These agree well with measured blood glucose values. Although major ischaemic failure was not seen in these patients, transient ischaemic events lasting 40 minutes and characterised by a lactate/glucose ratio increase to 2 were noticed. Finally, a quasi-periodic oscillatory pattern with inverse changes in glucose and lactate was observed during these patientsʼ monitoring. This was ascribed to gut peristalsis