论文标题
使用随机旋转设备的贝叶斯网络构建块的硬件实现
Hardware implementation of Bayesian network building blocks with stochastic spintronic devices
论文作者
论文摘要
贝叶斯网络是理解现实世界中概率问题(例如诊断,预测,计算机视觉等)中因果关系的强大统计模型。对于涉及许多变量中复杂因果关系的系统,相关贝叶斯网络的复杂性在计算上变得可分解。结果,这些网络的直接硬件实现是减少功耗和执行时间的一种有前途的方法。但是,文献中介绍的贝叶斯网络的少数硬件实现取决于确定性的CMOS设备,这些设备在表示贝叶斯网络中固有的随机变量方面效率不高。这项工作为贝叶斯网络构建块提供了一个实验证明,该贝叶斯网络构建块由自然随机的自旋设备实现。这些设备基于具有垂直磁各向异性的纳米磁铁,通过使用巨大的自旋霍尔效应的重金属下层旋转轨道扭矩初始化为硬轴,从而实现了随机行为。我们构建了两个随机设备的电气互连网络,并通过改变连接权重和偏见来操纵其状态之间的相关性。通过将给定的条件概率表映射到电路硬件,我们证明了我们的随机网络可以实现任何两个节点贝叶斯网络。然后,我们使用我们建议的设备介绍了四个节点贝叶斯网络的示例案例的随机模拟,并从实验中获取参数。我们将这项工作视为迈向贝叶斯网络大规模硬件实现的第一步。
Bayesian networks are powerful statistical models to understand causal relationships in real-world probabilistic problems such as diagnosis, forecasting, computer vision, etc. For systems that involve complex causal dependencies among many variables, the complexity of the associated Bayesian networks become computationally intractable. As a result, direct hardware implementation of these networks is one promising approach to reducing power consumption and execution time. However, the few hardware implementations of Bayesian networks presented in literature rely on deterministic CMOS devices that are not efficient in representing the inherently stochastic variables in a Bayesian network. This work presents an experimental demonstration of a Bayesian network building block implemented with naturally stochastic spintronic devices. These devices are based on nanomagnets with perpendicular magnetic anisotropy, initialized to their hard axes by the spin orbit torque from a heavy metal under-layer utilizing the giant spin Hall effect, enabling stochastic behavior. We construct an electrically interconnected network of two stochastic devices and manipulate the correlations between their states by changing connection weights and biases. By mapping given conditional probability tables to the circuit hardware, we demonstrate that any two node Bayesian networks can be implemented by our stochastic network. We then present the stochastic simulation of an example case of a four node Bayesian network using our proposed device, with parameters taken from the experiment. We view this work as a first step towards the large scale hardware implementation of Bayesian networks.