因子图是用于代表机器人技术各种问题的图形模型,例如运动(SFM),同时定位和映射(SLAM)和校准。通常,在他们的核心上,他们有一个优化问题,其术语仅取决于一小部分变量。因子图解决器利用问题的局部性,以大大减少迭代最小二乘(ILS)方法的计算时间。尽管非常强大,但他们的应用通常仅限于无约束的问题。在本文中,我们通过引入Lagrange乘数方法的因子图版本来对因子图内的变量进行建模。我们通过根据因子图提供完整的导航堆栈来显示我们方法的潜力。与标准导航堆栈不同,我们可以使用因子图对本地规划和本地化的最佳控制建模,并使用标准ILS方法来解决这两个问题。我们在现实世界自主导航方案中验证了我们的方法,并将其与ROS中实现的事实上的标准导航堆栈进行了比较。比较实验表明,对于手头的应用程序,我们的系统优于运行时的标准非线性编程求解器内部优化器(IPOPT),同时实现了类似的解决方案。
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姿势图优化是在机器人感知的许多领域遇到的非凸优化问题。它的收敛到准确的解决方案由两个因素来调节:使用成本函数的非线性和姿势变量的初始配置。在本文中,我们提出了Hipe,这是一种用于姿势图初始化的新型分层算法。我们的方法利用了一个粗粒图,该图编码了问题几何形状的抽象表示。我们通过结合来自输入本地区域的最大似然估计来构建此图。通过利用这种表示的稀疏性,我们可以以非线性方式初始化姿势图,而无需与现有方法相比,没有计算开销。最终的初始猜测可以有效地引导用于获得最终解决方案的细粒优化。此外,我们对不同成本函数对最终估计的影响进行了经验分析。我们的实验评估表明,HIPE的使用导致更有效,更健壮的优化过程,与最先进的方法相比。
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软件体系结构定义了大型计算系统的蓝图,因此是设计和开发工作的关键部分。在移动机器人的背景下,对此任务进行了广泛的探索,从而导致了大量参考设计和实现。由于软件体系结构定义了实现所有组件的框架,因此自然是移动机器人系统的一个非常重要的方面。在本章中,我们概述了特定问题域(移动机器人系统)对软件框架强加的要求。我们讨论了一些当前的设计解决方案,提供了有关共同框架的历史观点,并概述了未来发展的方向。
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传感器是将物理参数或环境特征(例如温度,距离,速度等)转换为可以通过数字测量和处理以执行特定任务的信号的设备。移动机器人需要传感器来测量其环境的属性,从而允许安全导航,复杂的感知和相应的动作以及与填充环境的其他代理的有效相互作用。移动机器人使用的传感器范围从简单的触觉传感器(例如保险杠)到复杂的基于视觉的传感器,例如结构化灯相机。所有这些都提供了可以由机器人计算机处理的数字输出(例如,字符串,一组值,矩阵等)。通常通过使用传感器中包含的数字转换器(ADC)的类似物来离散一个或多个模拟电信号来获得此类输出。在本章中,我们介绍了移动机器人技术中最常见的传感器,并提供了其分类法,基本特征和规格的介绍。对功能和应用程序类型的描述遵循一种自下而上的方法:在描述现实世界传感器之前,介绍了传感器所基于的基本原理和组件,这些传感器通常基于多种技术和基本设备。
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Accurate uncertainty quantification is necessary to enhance the reliability of deep learning models in real-world applications. In the case of regression tasks, prediction intervals (PIs) should be provided along with the deterministic predictions of deep learning models. Such PIs are useful or "high-quality'' as long as they are sufficiently narrow and capture most of the probability density. In this paper, we present a method to learn prediction intervals for regression-based neural networks automatically in addition to the conventional target predictions. In particular, we train two companion neural networks: one that uses one output, the target estimate, and another that uses two outputs, the upper and lower bounds of the corresponding PI. Our main contribution is the design of a loss function for the PI-generation network that takes into account the output of the target-estimation network and has two optimization objectives: minimizing the mean prediction interval width and ensuring the PI integrity using constraints that maximize the prediction interval probability coverage implicitly. Both objectives are balanced within the loss function using a self-adaptive coefficient. Furthermore, we apply a Monte Carlo-based approach that evaluates the model uncertainty in the learned PIs. Experiments using a synthetic dataset, six benchmark datasets, and a real-world crop yield prediction dataset showed that our method was able to maintain a nominal probability coverage and produce narrower PIs without detriment to its target estimation accuracy when compared to those PIs generated by three state-of-the-art neural-network-based methods.
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A quantitative assessment of the global importance of an agent in a team is as valuable as gold for strategists, decision-makers, and sports coaches. Yet, retrieving this information is not trivial since in a cooperative task it is hard to isolate the performance of an individual from the one of the whole team. Moreover, it is not always clear the relationship between the role of an agent and his personal attributes. In this work we conceive an application of the Shapley analysis for studying the contribution of both agent policies and attributes, putting them on equal footing. Since the computational complexity is NP-hard and scales exponentially with the number of participants in a transferable utility coalitional game, we resort to exploiting a-priori knowledge about the rules of the game to constrain the relations between the participants over a graph. We hence propose a method to determine a Hierarchical Knowledge Graph of agents' policies and features in a Multi-Agent System. Assuming a simulator of the system is available, the graph structure allows to exploit dynamic programming to assess the importances in a much faster way. We test the proposed approach in a proof-of-case environment deploying both hardcoded policies and policies obtained via Deep Reinforcement Learning. The proposed paradigm is less computationally demanding than trivially computing the Shapley values and provides great insight not only into the importance of an agent in a team but also into the attributes needed to deploy the policy at its best.
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In recent years there has been growing attention to interpretable machine learning models which can give explanatory insights on their behavior. Thanks to their interpretability, decision trees have been intensively studied for classification tasks, and due to the remarkable advances in mixed-integer programming (MIP), various approaches have been proposed to formulate the problem of training an Optimal Classification Tree (OCT) as a MIP model. We present a novel mixed-integer quadratic formulation for the OCT problem, which exploits the generalization capabilities of Support Vector Machines for binary classification. Our model, denoted as Margin Optimal Classification Tree (MARGOT), encompasses the use of maximum margin multivariate hyperplanes nested in a binary tree structure. To enhance the interpretability of our approach, we analyse two alternative versions of MARGOT, which include feature selection constraints inducing local sparsity of the hyperplanes. First, MARGOT has been tested on non-linearly separable synthetic datasets in 2-dimensional feature space to provide a graphical representation of the maximum margin approach. Finally, the proposed models have been tested on benchmark datasets from the UCI repository. The MARGOT formulation turns out to be easier to solve than other OCT approaches, and the generated tree better generalizes on new observations. The two interpretable versions are effective in selecting the most relevant features and maintaining good prediction quality.
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Hierarchical time series are common in several applied fields. Forecasts are required to be coherent, that is, to satisfy the constraints given by the hierarchy. The most popular technique to enforce coherence is called reconciliation, which adjusts the base forecasts computed for each time series. However, recent works on probabilistic reconciliation present several limitations. In this paper, we propose a new approach based on conditioning to reconcile any type of forecast distribution. We then introduce a new algorithm, called Bottom-Up Importance Sampling, to efficiently sample from the reconciled distribution. It can be used for any base forecast distribution: discrete, continuous, or in the form of samples, providing a major speedup compared to the current methods. Experiments on several temporal hierarchies show a significant improvement over base probabilistic forecasts.
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由于存在对抗性攻击,因此在安全至关重要系统中使用神经网络需要安全,可靠的模型。了解任何输入X的最小对抗扰动,或等效地知道X与分类边界的距离,可以评估分类鲁棒性,从而提供可认证的预测。不幸的是,计算此类距离的最新技术在计算上很昂贵,因此不适合在线应用程序。这项工作提出了一个新型的分类器家族,即签名的距离分类器(SDC),从理论的角度来看,它直接输出X与分类边界的确切距离,而不是概率分数(例如SoftMax)。 SDC代表一个强大的设计分类器家庭。为了实际解决SDC的理论要求,提出了一种名为Unitary级别神经网络的新型网络体系结构。实验结果表明,所提出的体系结构近似于签名的距离分类器,因此允许以单个推断为代价对X进行在线认证分类。
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联合学习是用于培训分布式,敏感数据的培训模型的流行策略,同时保留了数据隐私。先前的工作确定了毒害数据或模型的联合学习方案的一系列安全威胁。但是,联合学习是一个网络系统,客户与服务器之间的通信对于学习任务绩效起着至关重要的作用。我们强调了沟通如何在联邦学习中引入另一个漏洞表面,并研究网络级对手对训练联合学习模型的影响。我们表明,从精心选择的客户中删除网络流量的攻击者可以大大降低目标人群的模型准确性。此外,我们表明,来自少数客户的协调中毒运动可以扩大降低攻击。最后,我们开发了服务器端防御,通过识别和上采样的客户可能对目标准确性做出积极贡献,从而减轻了攻击的影响。我们在三个数据集上全面评估了我们的攻击和防御,假设具有网络部分可见性的加密通信渠道和攻击者。
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