Learning Mazes with Aliasing States: An LCS Algorithm with Associative Perception

Learning classifier systems (LCSs) belong to a class of algorithms based on the principle of self-organization and have frequently been applied to the task of solving mazes, an important type of reinforcement learning (RL) problem. Maze problems represent a simplified virtual model of real environments that can be used for developing core algorithms of many real-world applications related to the problem of navigation. However, the best achievements of LCSs in maze problems are still mostly bounded to non-aliasing environments, while LCS complexity seems to obstruct a proper analysis of the reasons of failure. We construct a new LCS agent that has a simpler and more transparent performance mechanism, but that can still solve mazes better than existing algorithms. We use the structure of a predictive LCS model, strip out the evolutionary mechanism, simplify the reinforcement learning procedure and equip the agent with the ability of associative perception, adopted from psychology. To improve our understanding of the nature and structure of maze environments, we analyze mazes used in research for the last two decades, introduce a set of maze complexity characteristics, and develop a set of new maze environments. We then run our new LCS with associative perception through the old and new aliasing mazes, which represent partially observable Markov decision problems (POMDP) and demonstrate that it performs at least as well as, and in some cases better than, other published systems

Encyclopedia of Drug Policy

Spanning two volumes of approximately 450 entries in an A-to-Z format, this encyclopedia explores the controversial drug war through the lens of varied disciplines. A full spectrum of articles explains topics from Colombian cartels and Mexican kingpins to television reportage; from just say no advertising to heroin production; and from narco-terrorism to more than $500 billion in U.S. government expenditures.https://digitalcommons.unomaha.edu/criminaljusticefacbooks/1013/thumbnail.jp

Pediatric firearm injury related emergency department visits and hospitalizations: a population-based study in the United StatesResearch in context

Summary: Background: Firearm injury (FI) is the leading cause of death in children and adolescents in the United States (US). We describe the epidemiology of pediatric FI-associated emergency department (ED) visits and hospitalizations in the US stratified by race and ethnicity. Methods: Data on pediatric (0–17-year-olds) FI were analyzed using the 2019 Nationwide Emergency Department Sample (NEDS) and Kids’ Inpatient Database (KID), the largest all-payer databases in the US for ED visits and pediatric hospitalizations, respectively. FI encounters were stratified by race and ethnicity. Poisson regression was used to identify factors associated with in-hospital mortality. Sampling weights were applied to generate nationally representative estimates. Findings: There were 7017 pediatric ED visits with FI (NEDS); 85.0% (5961/7017) were male and 73.0% (5125/7017) were adolescents (15–17 years). Overall, 5.5% (384/7017) died in the ED; 53.1% (3727/7017) of ED encounters did not result in hospitalization. There were 2817 pediatric FI hospitalizations (KID); 84.1% (2369/2817) were male and 71.6% (2018/2817) were adolescents; 51.4% (1447/2817) of FI were unintentional, 42.8% (1207/2817) were assault-related, and 5.8% (163/2817) were self-inflicted. Black children had the highest proportion (52.6%; 1481/2817) of hospitalizations among all race and ethnicities (p < 0.0001 vs. White). White children had the highest proportion of hospitalizations for self-inflicted injuries (16.6% [91/551] vs. 4.9% [25/504; p < 0.0001] in Hispanics and 1.7% [24/1481] in Blacks; p < 0.0001). The majority (56.5%; 1591/2817) of hospitalizations were patients from low-income zip codes (median annual-household-income <$44,000); 70% (1971/2817) had Medicaid as the primary insurance payer. Overall, 8.0% (225/2817) died during FI-associated hospitalizations. Self-inflicted injuries had the highest in-hospital mortality (prevalence ratio = 8.20, 95% CI = 6.06–11.10 vs. unintentional). Interpretation: Black children and children with lower household incomes were disproportionately impacted by FI resulting from assaults and accidents, while White children had the highest proportion of self-inflicted FI injuries. Public health and legal policy interventions are needed to prevent pediatric FI. Funding: US National Institutes of Health