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我已经建立了一个常规的ANN-BP设置，其中一个单元在输入和输出层以及4个隐藏的sigmoid节点。给它一个简单的任务来近似线性f(n) = n与范围0-100中的n。ANN回归，线性函数近似
问题：无论层，单元在隐藏层的数目的或是否我在节点使用偏置值都会了解来近似F（N）=平均（数据集），如下所示：
代码是用JavaScript编写的概念证明。我定义了三个类：Net，Layer和Connection，其中Layer是一个输入数组，偏移量和输出值，Connection是一个二维权重和三角权重数组。下面是层的代码，所有重要的计算发生：
Ann.Layer = function(nId, oNet, oConfig, bUseBias, aInitBiases) {
var _oThis = this;
var _initialize = function() {
_oThis.id = nId;
_oThis.length = oConfig.nodes;
_oThis.outputs = new Array(oConfig.nodes);
_oThis.inputs = new Array(oConfig.nodes);
_oThis.gradients = new Array(oConfig.nodes);
_oThis.biases = new Array(oConfig.nodes);
_oThis.outputs.fill(0);
_oThis.inputs.fill(0);
_oThis.biases.fill(0);
if (bUseBias) {
for (var n=0; n<oConfig.nodes; n++) {
_oThis.biases[n] = Ann.random(aInitBiases[0], aInitBiases[1]);
}
}
};
/****************** PUBLIC ******************/
this.id;
this.length;
this.inputs;
this.outputs;
this.gradients;
this.biases;
this.next;
this.previous;
this.inConnection;
this.outConnection;
this.isInput = function() { return !this.previous; }
this.isOutput = function() { return !this.next; }
this.calculateGradients = function(aTarget) {
var n, n1, nOutputError,
fDerivative = Ann.Activation.Derivative[oConfig.activation];
if (this.isOutput()) {
for (n=0; n<oConfig.nodes; n++) {
nOutputError = this.outputs[n] - aTarget[n];
this.gradients[n] = nOutputError * fDerivative(this.outputs[n]);
}
} else {
for (n=0; n<oConfig.nodes; n++) {
nOutputError = 0.0;
for (n1=0; n1<this.outConnection.weights[n].length; n1++) {
nOutputError += this.outConnection.weights[n][n1] * this.next.gradients[n1];
}
// console.log(this.id, nOutputError, this.outputs[n], fDerivative(this.outputs[n]));
this.gradients[n] = nOutputError * fDerivative(this.outputs[n]);
}
}
}
this.updateInputWeights = function() {
if (!this.isInput()) {
var nY,
nX,
nOldDeltaWeight,
nNewDeltaWeight;
for (nX=0; nX<this.previous.length; nX++) {
for (nY=0; nY<this.length; nY++) {
nOldDeltaWeight = this.inConnection.deltaWeights[nX][nY];
nNewDeltaWeight =
- oNet.learningRate
* this.previous.outputs[nX]
* this.gradients[nY]
// Add momentum, a fraction of old delta weight
+ oNet.learningMomentum
* nOldDeltaWeight;
if (nNewDeltaWeight == 0 && nOldDeltaWeight != 0) {
console.log('Double overflow');
}
this.inConnection.deltaWeights[nX][nY] = nNewDeltaWeight;
this.inConnection.weights[nX][nY] += nNewDeltaWeight;
}
}
}
}
this.updateInputBiases = function() {
if (bUseBias && !this.isInput()) {
var n,
nNewDeltaBias;
for (n=0; n<this.length; n++) {
nNewDeltaBias =
- oNet.learningRate
* this.gradients[n];
this.biases[n] += nNewDeltaBias;
}
}
}
this.feedForward = function(a) {
var fActivation = Ann.Activation[oConfig.activation];
this.inputs = a;
if (this.isInput()) {
this.outputs = this.inputs;
} else {
for (var n=0; n<a.length; n++) {
this.outputs[n] = fActivation(a[n] + this.biases[n]);
}
}
if (!this.isOutput()) {
this.outConnection.feedForward(this.outputs);
}
}
_initialize();
}
主要前馈和backProp函数定义，像这样：
this.feedForward = function(a) {
this.layers[0].feedForward(a);
this.netError = 0;
}
this.backPropagate = function(aExample, aTarget) {
this.target = aTarget;
if (aExample.length != this.getInputCount()) { throw "Wrong input count in training data"; }
if (aTarget.length != this.getOutputCount()) { throw "Wrong output count in training data"; }
this.feedForward(aExample);
_calculateNetError(aTarget);
var oLayer = null,
nLast = this.layers.length-1,
n;
for (n=nLast; n>0; n--) {
if (n === nLast) {
this.layers[n].calculateGradients(aTarget);
} else {
this.layers[n].calculateGradients();
}
}
for (n=nLast; n>0; n--) {
this.layers[n].updateInputWeights();
this.layers[n].updateInputBiases();
}
}
连接代码相当简单：
Ann.Connection = function(oNet, oConfig, aInitWeights) {
var _oThis = this;
var _initialize = function() {
var nX, nY, nIn, nOut;
_oThis.from = oNet.layers[oConfig.from];
_oThis.to = oNet.layers[oConfig.to];
nIn = _oThis.from.length;
nOut = _oThis.to.length;
_oThis.weights = new Array(nIn);
_oThis.deltaWeights = new Array(nIn);
for (nX=0; nX<nIn; nX++) {
_oThis.weights[nX] = new Array(nOut);
_oThis.deltaWeights[nX] = new Array(nOut);
_oThis.deltaWeights[nX].fill(0);
for (nY=0; nY<nOut; nY++) {
_oThis.weights[nX][nY] = Ann.random(aInitWeights[0], aInitWeights[1]);
}
}
};
/****************** PUBLIC ******************/
this.weights;
this.deltaWeights;
this.from;
this.to;
this.feedForward = function(a) {
var n, nX, nY, aOut = new Array(this.to.length);
for (nY=0; nY<this.to.length; nY++) {
n = 0;
for (nX=0; nX<this.from.length; nX++) {
n += a[nX] * this.weights[nX][nY];
}
aOut[nY] = n;
}
this.to.feedForward(aOut);
}
_initialize();
}
而且我的激活函数和派生类定义如下：
Ann.Activation = {
linear : function(n) { return n; },
sigma : function(n) { return 1.0/(1.0 + Math.exp(-n)); },
tanh : function(n) { return Math.tanh(n); }
}
Ann.Activation.Derivative = {
linear : function(n) { return 1.0; },
sigma : function(n) { return n * (1.0 - n); },
tanh : function(n) { return 1.0 - n * n; }
}
而且配置JSON如下：
var Config = {
id : "Config1",
learning_rate : 0.01,
learning_momentum : 0,
init_weight : [-1, 1],
init_bias : [-1, 1],
use_bias : false,
layers: [
{nodes : 1},
{nodes : 4, activation : "sigma"},
{nodes : 1, activation : "linear"}
],
connections: [
{from : 0, to : 1},
{from : 1, to : 2}
]
}
也许，你的经验眼可以用我的计算发现这个问题？
感谢您的关注，但我不明白：1）为什么我们在积累delta_weights？ 2）为什么我们需要4个隐藏层进行简单近似？ –
我错了积累，谢谢指出。至于深度，在其他轻微代码更改之后，它的效果更好。我减少了1,2,2,1 ...学习率0.06和动量0.04。总的来说，代码似乎比它更好。如果你不同意，那很好。我只是在学习时帮助。 –
谢谢。我刚刚注意到的另一件事，你已经删除了错误的平方，这允许一个错误标志潜入计算。这意味着负面的错误会消除循环中的正面错误，否则负面的错误可能会积累并阻止我们测量何时停止训练。 –