33 research outputs found
Landscape-Aware Fixed-Budget Performance Regression and Algorithm Selection for Modular CMA-ES Variants
Automated algorithm selection promises to support the user in the decisive
task of selecting a most suitable algorithm for a given problem. A common
component of these machine-trained techniques are regression models which
predict the performance of a given algorithm on a previously unseen problem
instance. In the context of numerical black-box optimization, such regression
models typically build on exploratory landscape analysis (ELA), which
quantifies several characteristics of the problem. These measures can be used
to train a supervised performance regression model.
First steps towards ELA-based performance regression have been made in the
context of a fixed-target setting. In many applications, however, the user
needs to select an algorithm that performs best within a given budget of
function evaluations. Adopting this fixed-budget setting, we demonstrate that
it is possible to achieve high-quality performance predictions with
off-the-shelf supervised learning approaches, by suitably combining two
differently trained regression models. We test this approach on a very
challenging problem: algorithm selection on a portfolio of very similar
algorithms, which we choose from the family of modular CMA-ES algorithms.Comment: To appear in Proc. of Genetic and Evolutionary Computation Conference
(GECCO'20
Per-run Algorithm Selection with Warm-starting using Trajectory-based Features
Per-instance algorithm selection seeks to recommend, for a given problem
instance and a given performance criterion, one or several suitable algorithms
that are expected to perform well for the particular setting. The selection is
classically done offline, using openly available information about the problem
instance or features that are extracted from the instance during a dedicated
feature extraction step. This ignores valuable information that the algorithms
accumulate during the optimization process.
In this work, we propose an alternative, online algorithm selection scheme
which we coin per-run algorithm selection. In our approach, we start the
optimization with a default algorithm, and, after a certain number of
iterations, extract instance features from the observed trajectory of this
initial optimizer to determine whether to switch to another optimizer. We test
this approach using the CMA-ES as the default solver, and a portfolio of six
different optimizers as potential algorithms to switch to. In contrast to other
recent work on online per-run algorithm selection, we warm-start the second
optimizer using information accumulated during the first optimization phase. We
show that our approach outperforms static per-instance algorithm selection. We
also compare two different feature extraction principles, based on exploratory
landscape analysis and time series analysis of the internal state variables of
the CMA-ES, respectively. We show that a combination of both feature sets
provides the most accurate recommendations for our test cases, taken from the
BBOB function suite from the COCO platform and the YABBOB suite from the
Nevergrad platform
PI is back! Switching Acquisition Functions in Bayesian Optimization
Bayesian Optimization (BO) is a powerful, sample-efficient technique to
optimize expensive-to-evaluate functions. Each of the BO components, such as
the surrogate model, the acquisition function (AF), or the initial design, is
subject to a wide range of design choices. Selecting the right components for a
given optimization task is a challenging task, which can have significant
impact on the quality of the obtained results. In this work, we initiate the
analysis of which AF to favor for which optimization scenarios. To this end, we
benchmark SMAC3 using Expected Improvement (EI) and Probability of Improvement
(PI) as acquisition functions on the 24 BBOB functions of the COCO environment.
We compare their results with those of schedules switching between AFs. One
schedule aims to use EI's explorative behavior in the early optimization steps,
and then switches to PI for a better exploitation in the final steps. We also
compare this to a random schedule and round-robin selection of EI and PI. We
observe that dynamic schedules oftentimes outperform any single static one. Our
results suggest that a schedule that allocates the first 25 % of the
optimization budget to EI and the last 75 % to PI is a reliable default.
However, we also observe considerable performance differences for the 24
functions, suggesting that a per-instance allocation, possibly learned on the
fly, could offer significant improvement over the state-of-the-art BO designs.Comment: 2022 NeurIPS Workshop on Gaussian Processes, Spatiotemporal Modeling,
and Decision-making System
CCR6 is expressed on an IL-10–producing, autoreactive memory T cell population with context-dependent regulatory function
Interleukin (IL)-10 produced by regulatory T cell subsets is important for the prevention of autoimmunity and immunopathology, but little is known about the phenotype and function of IL-10–producing memory T cells. Human CD4+CCR6+ memory T cells contained comparable numbers of IL-17– and IL-10–producing cells, and CCR6 was induced under both Th17-promoting conditions and upon tolerogenic T cell priming with transforming growth factor (TGF)–β. In normal human spleens, the majority of CCR6+ memory T cells were in the close vicinity of CCR6+ myeloid dendritic cells (mDCs), and strikingly, some of them were secreting IL-10 in situ. Furthermore, CCR6+ memory T cells produced suppressive IL-10 but not IL-2 upon stimulation with autologous immature mDCs ex vivo, and secreted IL-10 efficiently in response to suboptimal T cell receptor (TCR) stimulation with anti-CD3 antibodies. However, optimal TCR stimulation of CCR6+ T cells induced expression of IL-2, interferon-γ, CCL20, and CD40L, and autoreactive CCR6+ T cell lines responded to various recall antigens. Notably, we isolated autoreactive CCR6+ T cell clones with context-dependent behavior that produced IL-10 with autologous mDCs alone, but that secreted IL-2 and proliferated upon stimulation with tetanus toxoid. We propose the novel concept that a population of memory T cells, which is fully equipped to participate in secondary immune responses upon recognition of a relevant recall antigen, contributes to the maintenance of tolerance under steady-state conditions
Intestinal, extra-intestinal and systemic sequelae of Toxoplasma gondii induced acute ileitis in mice harboring a human gut microbiota
Background Within seven days following peroral high dose infection with
Toxoplasma gondii susceptible conventionally colonized mice develop acute
ileitis due to an underlying T helper cell (Th) -1 type immunopathology. We
here addressed whether mice harboring a human intestinal microbiota developed
intestinal, extra-intestinal and systemic sequelae upon ileitis induction.
Methodology/Principal findings Secondary abiotic mice were generated by broad-
spectrum antibiotic treatment and associated with a complex human intestinal
microbiota following peroral fecal microbiota transplantation. Within three
weeks the human microbiota had stably established in the murine intestinal
tract as assessed by quantitative cultural and culture-independent (i.e.
molecular 16S rRNA based) methods. At day 7 post infection (p.i.) with 50
cysts of T. gondii strain ME49 by gavage human microbiota associated (hma)
mice displayed severe clinical, macroscopic and microscopic sequelae
indicating acute ileitis. In diseased hma mice increased numbers of innate and
adaptive immune cells within the ileal mucosa and lamina propria and elevated
intestinal secretion of pro-inflammatory mediators including IFN-γ, IL-12 and
nitric oxide could be observed at day 7 p.i. Ileitis development was
accompanied by substantial shifts in intestinal microbiota composition of hma
mice characterized by elevated total bacterial loads and increased numbers of
intestinal Gram-negative commensals such as enterobacteria and Bacteroides /
Prevotella species overgrowing the small and large intestinal lumen.
Furthermore, viable bacteria translocated from the inflamed ileum to extra-
intestinal including systemic compartments. Notably, pro-inflammatory immune
responses were not restricted to the intestinal tract as indicated by
increased pro-inflammatory cytokine secretion in extra-intestinal (i.e. liver
and kidney) and systemic compartments including spleen and serum.
Conclusion/Significance With respect to the intestinal microbiota composition
“humanized” mice display acute ileitis following peroral high dose T. gondii
infection. Thus, hma mice constitute a suitable model to further dissect the
interactions between pathogens, human microbiota and vertebrate host immunity
during acute intestinal inflammation
Nucleotide-Oligomerization-Domain-2 Affects Commensal Gut Microbiota Composition and Intracerebral Immunopathology in Acute Toxoplasma gondii Induced Murine Ileitis
Background Within one week following peroral high dose infection with
Toxoplasma (T.) gondii, susceptible mice develop non-selflimiting acute
ileitis due to an underlying Th1-type immunopathology. The role of the innate
immune receptor nucleotide-oligomerization-domain-2 (NOD2) in mediating
potential extra-intestinal inflammatory sequelae including the brain, however,
has not been investigated so far. Methodology/Principal Findings Following
peroral infection with 100 cysts of T. gondii strain ME49, NOD2-/- mice
displayed more severe ileitis and higher small intestinal parasitic loads as
compared to wildtype (WT) mice. However, systemic (i.e. splenic) levels of
pro-inflammatory cytokines such as TNF-α and IFN-γ were lower in NOD2-/- mice
versus WT controls at day 7 p.i. Given that the immunopathological outcome
might be influenced by the intestinal microbiota composition, which is shaped
by NOD2, we performed a quantitative survey of main intestinal bacterial
groups by 16S rRNA analysis. Interestingly, Bifidobacteria were virtually
absent in NOD2-/- but not WT mice, whereas differences in remaining bacterial
species were rather subtle. Interestingly, more distinct intestinal
inflammation was accompanied by higher bacterial translocation rates to extra-
intestinal tissue sites such as liver, spleen, and kidneys in T. gondii
infected NOD2-/- mice. Strikingly, intracerebral inflammatory foci could be
observed as early as seven days following T. gondii infection irrespective of
the genotype of animals, whereas NOD2-/- mice exhibited higher intracerebral
parasitic loads, higher F4/80 positive macrophage and microglia numbers as
well as higher IFN-γ mRNA expression levels as compared to WT control animals.
Conclusion/Significance NOD2 signaling is involved in protection of mice from
T. gondii induced acute ileitis. The parasite-induced Th1-type immunopathology
at intestinal as well as extra-intestinal sites including the brain is
modulated in a NOD2-dependent manner
Prevalence, associated factors and outcomes of pressure injuries in adult intensive care unit patients: the DecubICUs study
Funder: European Society of Intensive Care Medicine; doi: http://dx.doi.org/10.13039/501100013347Funder: Flemish Society for Critical Care NursesAbstract: Purpose: Intensive care unit (ICU) patients are particularly susceptible to developing pressure injuries. Epidemiologic data is however unavailable. We aimed to provide an international picture of the extent of pressure injuries and factors associated with ICU-acquired pressure injuries in adult ICU patients. Methods: International 1-day point-prevalence study; follow-up for outcome assessment until hospital discharge (maximum 12 weeks). Factors associated with ICU-acquired pressure injury and hospital mortality were assessed by generalised linear mixed-effects regression analysis. Results: Data from 13,254 patients in 1117 ICUs (90 countries) revealed 6747 pressure injuries; 3997 (59.2%) were ICU-acquired. Overall prevalence was 26.6% (95% confidence interval [CI] 25.9–27.3). ICU-acquired prevalence was 16.2% (95% CI 15.6–16.8). Sacrum (37%) and heels (19.5%) were most affected. Factors independently associated with ICU-acquired pressure injuries were older age, male sex, being underweight, emergency surgery, higher Simplified Acute Physiology Score II, Braden score 3 days, comorbidities (chronic obstructive pulmonary disease, immunodeficiency), organ support (renal replacement, mechanical ventilation on ICU admission), and being in a low or lower-middle income-economy. Gradually increasing associations with mortality were identified for increasing severity of pressure injury: stage I (odds ratio [OR] 1.5; 95% CI 1.2–1.8), stage II (OR 1.6; 95% CI 1.4–1.9), and stage III or worse (OR 2.8; 95% CI 2.3–3.3). Conclusion: Pressure injuries are common in adult ICU patients. ICU-acquired pressure injuries are associated with mainly intrinsic factors and mortality. Optimal care standards, increased awareness, appropriate resource allocation, and further research into optimal prevention are pivotal to tackle this important patient safety threat
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Prevalence, associated factors and outcomes of pressure injuries in adult intensive care unit patients: the DecubICUs study
Funder: European Society of Intensive Care Medicine; doi: http://dx.doi.org/10.13039/501100013347Funder: Flemish Society for Critical Care NursesAbstract: Purpose: Intensive care unit (ICU) patients are particularly susceptible to developing pressure injuries. Epidemiologic data is however unavailable. We aimed to provide an international picture of the extent of pressure injuries and factors associated with ICU-acquired pressure injuries in adult ICU patients. Methods: International 1-day point-prevalence study; follow-up for outcome assessment until hospital discharge (maximum 12 weeks). Factors associated with ICU-acquired pressure injury and hospital mortality were assessed by generalised linear mixed-effects regression analysis. Results: Data from 13,254 patients in 1117 ICUs (90 countries) revealed 6747 pressure injuries; 3997 (59.2%) were ICU-acquired. Overall prevalence was 26.6% (95% confidence interval [CI] 25.9–27.3). ICU-acquired prevalence was 16.2% (95% CI 15.6–16.8). Sacrum (37%) and heels (19.5%) were most affected. Factors independently associated with ICU-acquired pressure injuries were older age, male sex, being underweight, emergency surgery, higher Simplified Acute Physiology Score II, Braden score 3 days, comorbidities (chronic obstructive pulmonary disease, immunodeficiency), organ support (renal replacement, mechanical ventilation on ICU admission), and being in a low or lower-middle income-economy. Gradually increasing associations with mortality were identified for increasing severity of pressure injury: stage I (odds ratio [OR] 1.5; 95% CI 1.2–1.8), stage II (OR 1.6; 95% CI 1.4–1.9), and stage III or worse (OR 2.8; 95% CI 2.3–3.3). Conclusion: Pressure injuries are common in adult ICU patients. ICU-acquired pressure injuries are associated with mainly intrinsic factors and mortality. Optimal care standards, increased awareness, appropriate resource allocation, and further research into optimal prevention are pivotal to tackle this important patient safety threat
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Correction to: Prevalence, associated factors and outcomes of pressure injuries in adult intensive care unit patients: the DecubICUs study
The original version of this article unfortunately contained a mistake
Vers une sélection en ligne d'algorithmes tenant compte du paysage dans l'optimisation numérique de boîte noire
Black-box optimization algorithms (BBOAs) are conceived for settings in which exact problem formulations are non-existent, inaccessible, or too complex for an analytical solution. BBOAs are essentially the only means of finding a good solution to such problems. Due to their general applicability, BBOAs can exhibit different behaviors when optimizing different types of problems. This yields a meta-optimization problem of choosing the best suited algorithm for a particular problem, called the algorithm selection (AS) problem. By reason of inherent human bias and limited expert knowledge, the vision of automating the selection process has quickly gained traction in the community. One prominent way of doing so is via so-called landscape-aware AS, where the choice of the algorithm is based on predicting its performance by means of numerical problem instance representations called features. A key challenge that landscape-aware AS faces is the computational overhead of extracting the features, a step typically designed to precede the actual optimization. In this thesis, we propose a novel trajectory-based landscape-aware AS approach which incorporates the feature extraction step within the optimization process. We show that the features computed using the search trajectory samples lead to robust and reliable predictions of algorithm performance, and to powerful algorithm selection models built atop. We also present several preparatory analyses, including a novel perspective of combining two complementary regression strategies that outperforms any of the classical, single regression models, to amplify the quality of the final selector.Les algorithmes d'optimisation de boîte noire (BBOA) sont conçus pour des scénarios où les formulations exactes de problèmes sont inexistantes, inaccessibles, ou trop complexes pour la résolution analytique. Les BBOA sont le seul moyen de trouver une bonne solution à un tel problème. En raison de leur applicabilité générale, les BBOA présentent des comportements différents lors de l'optimisation de différents types de problèmes. Cela donne un problème de méta-optimisation consistant à choisir l'algorithme le mieux adapté à un problème particulier, appelé problème de sélection d'algorithmes (AS). La vision d'automatiser cette sélection a vite gagné du terrain dans la communauté. Un moyen important de le faire est l'AS tenant compte du paysage, où le choix de l'algorithme est basé sur la prédiction de ses performances via des représentations numériques d'instances de problèmes appelées caractéristiques. Un défi clé auquel l'AS tenant compte du paysage est confrontée est le coût de calcul de l'extraction des caractéristiques, une étape qui précède l'optimisation. Dans cette thèse, nous proposons une approche d'AS tenant compte du paysage basée sur la trajectoire de recherche qui intègre cette étape d'extraction dans celle d'optimisation. Nous montrons que les caractéristiques calculées à l'aide de la trajectoire conduisent à des prédictions robustes et fiables des performances des algorithmes, et à de puissants modèles d'AS construits dessus. Nous présentons aussi plusieurs analyses préparatoires, y compris une perspective de combinaison de 2 stratégies de régression complémentaires qui surpasse des modèles classiques de régression simple et amplifie la qualité du sélecteur