演化神经网络学习方法及其应用

A learning method for evolutionary neural networks and its application

在基于梯度下降原理的ＢＰ网络学习过程中，权值的获取方法是采用某个确定的权值变化规则，然后在训练中逐步调整，最终得到一个较好的权值分布。但它往往会因非线性多极值目标函数而陷于局部最优解。本文采用全局寻优的遗传算法（ＧＡ）和基于梯度下降的局部寻优反传算法（ＢＰ）相结合来训练网络，使网络的连接权在不断迭代过程中自适应演化。通过在ＮＨ地区利用井旁道地震特征参数外推重建井底以下声波曲线的实践，表明这种演化学习方法可以克服传统方法的不足，而且还能避免训练中的“伪学习”现象，提高网络的推广预测能力。

During the learning process of back-propagation (BP) networks based on gradient descent principle, a good weighting value distribution can be finally obtained from adopting certain definite rule of weights variation and then gradually adjusting it in training in ordinary method, but it usually falls into local optimal solution because of nonlinear multi-extreme object function. Training networks combining genetic algorithm (GA ) based on global optimization with backpropagation (BP) based on gradient descent in the paper make the linking weights of networks self-adaptive evolution in constantly iterative process. The practice reconstructing sonic logging under bottom hole in NH area by extrapolating seismic characteristic parameters of near-well bore traces shows that the evolutionary learning method can overcome shortcomings of traditional method, and avoid “pseudo-learning”phenomenon in the training and improve popularizing and predicting ability for networks.