Efficient Meta Neural Heuristic for Multi-Objective Combinatorial Optimization

Recently, neural heuristics based on deep reinforcement learning have exhibited promise in solving multi-objective combinatorial optimization problems (MOCOPs). However, they are still struggling to achieve high learning efficiency and solution quality. To tackle this issue, we propose an efficient meta neural heuristic (EMNH), in which a meta-model is first trained and then fine-tuned with a few steps to solve corresponding single-objective subproblems. Specifically, for the training process, a (partial) architecture-shared multi-task model is leveraged to achieve parallel learning for the meta-model, so as to speed up the training; meanwhile, a scaled symmetric sampling method with respect to the weight vectors is designed to stabilize the training. For the fine-tuning process, an efficient hierarchical method is proposed to systematically tackle all the subproblems. Experimental results on the multi-objective traveling salesman problem (MOTSP), multi-objective capacitated vehicle routing problem (MOCVRP), and multi-objective knapsack problem (MOKP) show that, EMNH is able to outperform the state-of-the-art neural heuristics in terms of solution quality and learning efficiency, and yield competitive solutions to the strong traditional heuristics while consuming much shorter time.Comment: Accepted at NeurIPS 202

Neural Multi-Objective Combinatorial Optimization with Diversity Enhancement

Most of existing neural methods for multi-objective combinatorial optimization (MOCO) problems solely rely on decomposition, which often leads to repetitive solutions for the respective subproblems, thus a limited Pareto set. Beyond decomposition, we propose a novel neural heuristic with diversity enhancement (NHDE) to produce more Pareto solutions from two perspectives. On the one hand, to hinder duplicated solutions for different subproblems, we propose an indicator-enhanced deep reinforcement learning method to guide the model, and design a heterogeneous graph attention mechanism to capture the relations between the instance graph and the Pareto front graph. On the other hand, to excavate more solutions in the neighborhood of each subproblem, we present a multiple Pareto optima strategy to sample and preserve desirable solutions. Experimental results on classic MOCO problems show that our NHDE is able to generate a Pareto front with higher diversity, thereby achieving superior overall performance. Moreover, our NHDE is generic and can be applied to different neural methods for MOCO.Comment: Accepted at NeurIPS 202

Effects of Resistant Starch Infusion, Solely and Mixed with Xylan or Cellulose, on Gut Microbiota Composition in Ileum-Cannulated Pigs

Fermentation of dietary fiber (DF) is beneficial for gut health, but its prebiotic effects are often impeded in the distal large intestine because of the fast degradation of fermentable substrates. One way to enhance the prebiotic effect of DF is to deliver fibers to the lower parts of the gut, which can be achieved by mixing different kinds of fiber. Therefore, in the present study, an ileum-cannulated pig model was employed to investigate the fermentation influence in the large intestine by infusing resistant starch solely (RS, fast fermentable fiber) and mixing with other fibers (xylan or cellulose). Twenty-four ileum-cannulated growing pigs were divided into four groups: one control group receiving saline ileal infusions and three experimental groups infused with RS, RS with xylan, or RS with cellulose. Fecal and plasma samples were analyzed for gut microbiota composition, short-chain fatty acids (SCFAs), and blood biochemistry. Results indicated no significant differences between the RS and control group for the microbiome and SCFA concentration (p > 0.05). However, RS combined with fibers, particularly xylan, resulted in enhanced and prolonged fermentation, marked by an increase in Blautia and higher lactate and acetate production (p p p > 0.05), though a trend of increased glucose levels was noted in the treatment groups (p < 0.1). Overall, RS alone had a limited impact on the distal hindgut microbiota due to rapid fermentation in the proximal gut, whereas combining RS with other fibers notably improved gut microecology by extending the fermentation process

Effect of no eyeglasses sales on the quality of eye care: an experimental evidence from China

Abstract Background Eye examinations and eyeglasses acquisition are typically integrated into a cohesive procedure in China. We conducted a randomized controlled trial using incognito standardized patient (SP) approach to evaluate the impact of separating eyeglasses sales on the accuracy of final prescription. Methods 52 SPs were trained to provide standardized responses during eye examinations, and undergoing refraction by a senior ophthalmologist at a national-level clinical center. SPs subsequently received eye examinations at 226 private optical shops and public hospitals in Shaanxi, northwestern China. The visits were randomly assigned to either control group, where SPs would typically purchase eyeglasses after refraction, or treatment group, where SPs made an advance declaration not to purchase eyeglasses prior to refraction. The dioptric difference between the final prescriptions provided by local refractionists and expert in the better-seeing eye was determined using the Vector Diopteric Distance method, and the completeness of exams was assessed against national standards. Multiple regressions were conducted to estimate the impact of no eyeglasses sales on the accuracy of the final prescription of local refractionists, as well as the completeness of examinations. Results Among 226 eye exams (73 in public hospitals, 153 in private optical shops), 133 (58.8%) were randomized to control group and 93 (41.2%) to no eyeglasses sales group. The inaccuracy rate of final prescriptions provided by local refractionists (≥ 1.0 D, experts’ final prescription as the reference) was 25.6% in control group, while 36.6% in no-sale group (P = 0.077). The likelihood of providing inaccurate final prescriptions was significantly higher in no-sale group compared to control group (OR = 1.607; 95% CI: 1.030 to 2.508; P = 0.037). This was particularly evident in private optical shops (OR = 2.433; 95% CI: 1.386 to 4.309; P = 0.002). In terms of process quality, the no-sale group performed significantly less subjective refraction (OR = 0.488; 95% CI: 0.253 to 0.940; P = 0.032) and less testing SP’s own eyeglasses (OR = 0.424; 95% CI: 0.201 to 0.897; P = 0.025). The duration of eye exams was 3.917 min shorter (95% CI: -6.798 to -1.036; P = 0.008) in no-sale group. Conclusions Separating eyeglasses sales from optical care could lead to worse quality of eye care. Policy makers should carefully consider the role of economic incentives in healthcare reform