如何用Deeplearning4j实现GAN

一、Gan的思想

    Gan的核心所做的事情是在解决一个argminmax的问题，公式：

    1、求解一个Discriminator，可以最大尺度的丈量Generator 产生的数据和真实数据之间的分布距离

    2、求解一个Generator，可以最大程度减小产生数据和真实数据之间的距离

    gan的原始公式如下：

    实际上，我们不可能真求期望，只能sample出data来近似求解，于是，公式变成如下：

    于是，求解V的最大值，变成了一个二分类问题，变成了求交叉熵的最小值。

二、代码

public class Gan { static double lr = 0.01; public static void main(String[] args) throws Exception { final NeuralNetConfiguration.Builder builder = new NeuralNetConfiguration.Builder().updater(new Sgd(lr)) .weightInit(WeightInit.XAVIER); final GraphBuilder graphBuilder = builder.graphBuilder().backpropType(BackpropType.Standard) .addInputs("input1", "input2") .addLayer("g1", new DenseLayer.Builder().nIn(10).nOut(128).activation(Activation.RELU) .weightInit(WeightInit.XAVIER).build(), "input1") .addLayer("g2", new DenseLayer.Builder().nIn(128).nOut(512).activation(Activation.RELU) .weightInit(WeightInit.XAVIER).build(), "g1") .addLayer("g3", new DenseLayer.Builder().nIn(512).nOut(28 * 28).activation(Activation.RELU) .weightInit(WeightInit.XAVIER).build(), "g2") .addVertex("stack", new StackVertex(), "input2", "g3") .addLayer("d1", new DenseLayer.Builder().nIn(28 * 28).nOut(256).activation(Activation.RELU) .weightInit(WeightInit.XAVIER).build(), "stack") .addLayer("d2", new DenseLayer.Builder().nIn(256).nOut(128).activation(Activation.RELU) .weightInit(WeightInit.XAVIER).build(), "d1") .addLayer("d3", new DenseLayer.Builder().nIn(128).nOut(128).activation(Activation.RELU) .weightInit(WeightInit.XAVIER).build(), "d2") .addLayer("out", new OutputLayer.Builder(LossFunctions.LossFunction.XENT).nIn(128).nOut(1) .activation(Activation.SIGMOID).build(), "d3") .setOutputs("out"); ComputationGraph net = new ComputationGraph(graphBuilder.build()); net.init(); System.out.println(net.summary()); UIServer uiServer = UIServer.getInstance(); StatsStorage statsStorage = new InMemoryStatsStorage(); uiServer.attach(statsStorage); net.setListeners(new ScoreIterationListener(100)); net.getLayers(); DataSetIterator train = new MnistDataSetIterator(30, true, 12345); INDArray labelD = Nd4j.vstack(Nd4j.ones(30, 1), Nd4j.zeros(30, 1)); INDArray labelG = Nd4j.ones(60, 1); for (int i = 1; i <= 100000; i++) { if (!train.hasNext()) { train.reset(); } INDArray trueExp = train.next().getFeatures(); INDArray z = Nd4j.rand(new long[] { 30, 10 }, new NormalDistribution()); MultiDataSet dataSetD = new org.nd4j.linalg.dataset.MultiDataSet(new INDArray[] { z, trueExp }, new INDArray[] { labelD }); for(int m=0;m<10;m++){ trainD(net, dataSetD); } z = Nd4j.rand(new long[] { 30, 10 }, new NormalDistribution()); MultiDataSet dataSetG = new org.nd4j.linalg.dataset.MultiDataSet(new INDArray[] { z, trueExp }, new INDArray[] { labelG }); trainG(net, dataSetG); if (i % 10000 == 0) { net.save(new File("E:/gan.zip"), true); } } } public static void trainD(ComputationGraph net, MultiDataSet dataSet) { net.setLearningRate("g1", 0); net.setLearningRate("g2", 0); net.setLearningRate("g3", 0); net.setLearningRate("d1", lr); net.setLearningRate("d2", lr); net.setLearningRate("d3", lr); net.setLearningRate("out", lr); net.fit(dataSet); } public static void trainG(ComputationGraph net, MultiDataSet dataSet) { net.setLearningRate("g1", lr); net.setLearningRate("g2", lr); net.setLearningRate("g3", lr); net.setLearningRate("d1", 0); net.setLearningRate("d2", 0); net.setLearningRate("d3", 0); net.setLearningRate("out", 0); net.fit(dataSet); } }

    说明：

    1、dl4j并没有提供像keras那样冻结某些层参数的方法，这里采用设置learningrate为0的方法，来冻结某些层的参数

    2、这个的更新器，用的是sgd，不能用其他的（比方说Adam、Rmsprop），因为这些自适应更新器会考虑前面batch的梯度作为本次更新的梯度，达不到不更新参数的目的

    3、这里用了StackVertex，沿着第一维合并张量，也就是合并真实数据样本和Generator产生的数据样本，共同训练Discriminator

    4、训练过程中多次update   Discriminator的参数，以便量出最大距离，让后更新Generator一次

    5、进行10w次迭代

三、Generator生成手写数字

    加载训练好的模型，随机从NormalDistribution取出一些噪音数据，丢给模型，经过feedForward，取出最后一层Generator的激活值，便是我们想要的结果，代码如下：

public class LoadGan { public static void main(String[] args) throws Exception { ComputationGraph restored = ComputationGraph.load(new File("E:/gan.zip"), true); DataSetIterator train = new MnistDataSetIterator(30, true, 12345); INDArray trueExp = train.next().getFeatures(); Map<String, INDArray> map = restored.feedForward( new INDArray[] { Nd4j.rand(new long[] { 50, 10 }, new NormalDistribution()), trueExp }, false); INDArray indArray = map.get("g3");// .reshape(20,28,28); List<INDArray> list = new ArrayList<>(); for (int j = 0; j < indArray.size(0); j++) { list.add(indArray.getRow(j)); } MNISTVisualizer bestVisualizer = new MNISTVisualizer(1, list, "Gan"); bestVisualizer.visualize(); } public static class MNISTVisualizer { private double imageScale; private List<INDArray> digits; // Digits (as row vectors), one per // INDArray private String title; private int gridWidth; public MNISTVisualizer(double imageScale, List<INDArray> digits, String title) { this(imageScale, digits, title, 5); } public MNISTVisualizer(double imageScale, List<INDArray> digits, String title, int gridWidth) { this.imageScale = imageScale; this.digits = digits; this.title = title; this.gridWidth = gridWidth; } public void visualize() { JFrame frame = new JFrame(); frame.setTitle(title); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); JPanel panel = new JPanel(); panel.setLayout(new GridLayout(0, gridWidth)); List<JLabel> list = getComponents(); for (JLabel image : list) { panel.add(image); } frame.add(panel); frame.setVisible(true); frame.pack(); } public List<JLabel> getComponents() { List<JLabel> images = new ArrayList<>(); for (INDArray arr : digits) { BufferedImage bi = new BufferedImage(28, 28, BufferedImage.TYPE_BYTE_GRAY); for (int i = 0; i < 784; i++) { bi.getRaster().setSample(i % 28, i / 28, 0, (int) (255 * arr.getDouble(i))); } ImageIcon orig = new ImageIcon(bi); Image imageScaled = orig.getImage().getScaledInstance((int) (imageScale * 28), (int) (imageScale * 28), Image.SCALE_DEFAULT); ImageIcon scaled = new ImageIcon(imageScaled); images.add(new JLabel(scaled)); } return images; } } }

    实际效果，还算比较清晰

 

 

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