构建BP神经网络，源码。BP网络能学习和存贮大量的输入-输出模式映射关系，而无需事前揭示描述这种映射关系的数学方程。它的学习规则是使用最速下降法，通过反向传播来不断调整网络的权值和阈值，使网络的误差平方和最小。BP神经网络模型拓扑结构包括输入层（input）、隐层(hide layer)和输出层(output layer)。-BP neural network to build, source. BP network can learn and store a lot of input- output model mapping, without having to reveal in advance the mathematical descr iption of the mapping equation. Its learning rule is to use the steepest descent method, by back-propagation network to continuously adjust the weights and threshold, the network and the minimum square error. BP neural network model topology including input layer (input), hidden (hide layer) and output layer (output layer).