bp神经网络鸢尾花java

好的，以下是使用Java实现BP神经网络进行鸢尾花分类的示例代码：

首先，我们需要定义一个BP神经网络类，包含输入层、隐藏层和输出层，并实现前向传播和反向传播算法。

public class BPNeuralNetwork {
    private double[][] inputLayer;
    private double[][] hiddenLayer;
    private double[][] outputLayer;

    private double[][] inputWeights;
    private double[][] hiddenWeights;

    private double[] inputBias;
    private double[] hiddenBias;

    private double learningRate;
    private double momentum;

    public BPNeuralNetwork(int inputNodes, int hiddenNodes, int outputNodes, double learningRate, double momentum) {
        this.inputLayer = new double[1][inputNodes];
        this.hiddenLayer = new double[1][hiddenNodes];
        this.outputLayer = new double[1][outputNodes];

        this.inputWeights = new double[inputNodes][hiddenNodes];
        this.hiddenWeights = new double[hiddenNodes][outputNodes];

        this.inputBias = new double[hiddenNodes];
        this.hiddenBias = new double[outputNodes];

        this.learningRate = learningRate;
        this.momentum = momentum;

        Random rand = new Random();

        for (int i = 0; i < inputNodes; i++) {
            for (int j = 0; j < hiddenNodes; j++) {
                inputWeights[i][j] = rand.nextDouble() - 0.5;
            }
        }

        for (int i = 0; i < hiddenNodes; i++) {
            for (int j = 0; j < outputNodes; j++) {
                hiddenWeights[i][j] = rand.nextDouble() - 0.5;
            }
        }

        for (int i = 0; i < hiddenNodes; i++) {
            inputBias[i] = rand.nextDouble() - 0.5;
        }

        for (int i = 0; i < outputNodes; i++) {
            hiddenBias[i] = rand.nextDouble() - 0.5;
        }
    }

    public double sigmoid(double x) {
        return 1 / (1 + Math.exp(-x));
    }

    public double sigmoidDerivative(double x) {
        return x * (1 - x);
    }

    public double[][] forwardPropagation(double[][] inputs) {
        inputLayer = inputs;

        for (int i = 0; i < hiddenLayer[0].length; i++) {
            double sum = 0;
            for (int j = 0; j < inputLayer[0].length; j++) {
                sum += inputLayer[0][j] * inputWeights[j][i];
            }
            hiddenLayer[0][i] = sigmoid(sum + inputBias[i]);
        }

        for (int i = 0; i < outputLayer[0].length; i++) {
            double sum = 0;
            for (int j = 0; j < hiddenLayer[0].length; j++) {
                sum += hiddenLayer[0][j] * hiddenWeights[j][i];
            }
            outputLayer[0][i] = sigmoid(sum + hiddenBias[i]);
        }

        return outputLayer;
    }

    public void backPropagation(double[][] inputs, double[][] targets) {
        double[][] outputErrors = new double[1][outputLayer[0].length];
        double[][] hiddenErrors = new double[1][hiddenLayer[0].length];

        for (int i = 0; i < outputLayer[0].length; i++) {
            outputErrors[0][i] = (targets[0][i] - outputLayer[0][i]) * sigmoidDerivative(outputLayer[0][i]);
        }

        for (int i = 0; i < hiddenLayer[0].length; i++) {
            double sum = 0;
            for (int j = 0; j < outputLayer[0].length; j++) {
                sum += outputErrors[0][j] * hiddenWeights[i][j];
            }
            hiddenErrors[0][i] = sum * sigmoidDerivative(hiddenLayer[0][i]);
        }

        for (int i = 0; i < inputLayer[0].length; i++) {
            for (int j = 0; j < hiddenLayer[0].length; j++) {
                double weightDelta = learningRate * hiddenErrors[0][j] * inputLayer[0][i] + momentum * inputWeights[i][j];
                inputWeights[i][j] += weightDelta;
            }
        }

        for (int i = 0; i < hiddenLayer[0].length; i++) {
            for (int j = 0; j < outputLayer[0].length; j++) {
                double weightDelta = learningRate * outputErrors[0][j] * hiddenLayer[0][i] + momentum * hiddenWeights[i][j];
                hiddenWeights[i][j] += weightDelta;
            }
        }

        for (int i = 0; i < hiddenLayer[0].length; i++) {
            double biasDelta = learningRate * hiddenErrors[0][i];
            inputBias[i] += biasDelta;
        }

        for (int i = 0; i < outputLayer[0].length; i++) {
            double biasDelta = learningRate * outputErrors[0][i];
            hiddenBias[i] += biasDelta;
        }
    }
}

然后，我们需要读取鸢尾花数据集并进行预处理。

public class IrisData {
    private double[][] inputs;
    private double[][] targets;

    public double[][] getInputs() {
        return inputs;
    }

    public double[][] getTargets() {
        return targets;
    }

    public IrisData(String filename) {
        ArrayList<double[]> inputsList = new ArrayList<>();
        ArrayList<double[]> targetsList = new ArrayList<>();

        try {
            BufferedReader reader = new BufferedReader(new FileReader(filename));
            String line;

            while ((line = reader.readLine()) != null) {
                String[] values = line.split(",");

                double[] input = new double[4];
                input[0] = Double.parseDouble(values[0]);
                input[1] = Double.parseDouble(values[1]);
                input[2] = Double.parseDouble(values[2]);
                input[3] = Double.parseDouble(values[3]);
                inputsList.add(input);

                double[] target = new double[3];
                if (values[4].equals("Iris-setosa")) {
                    target[0] = 1;
                } else if (values[4].equals("Iris-versicolor")) {
                    target[1] = 1;
                } else if (values[4].equals("Iris-virginica")) {
                    target[2] = 1;
                }
                targetsList.add(target);
            }
            reader.close();
        } catch (Exception e) {
            e.printStackTrace();
        }

        inputs = new double[inputsList.size()][4];
        targets = new double[targetsList.size()][3];

        for (int i = 0; i < inputsList.size(); i++) {
            inputs[i] = inputsList.get(i);
            targets[i] = targetsList.get(i);
        }
    }
}

最后，我们可以使用BP神经网络进行训练和预测。

public class IrisClassifier {
    public static void main(String[] args) {
        IrisData data = new IrisData("iris.csv");
        BPNeuralNetwork network = new BPNeuralNetwork(4, 5, 3, 0.1, 0.9);

        for (int i = 0; i < 1000; i++) {
            for (int j = 0; j < data.getInputs().length; j++) {
                double[][] inputs = new double[1][4];
                inputs[0] = data.getInputs()[j];

                double[][] targets = new double[1][3];
                targets[0] = data.getTargets()[j];

                network.forwardPropagation(inputs);
                network.backPropagation(inputs, targets);
            }
        }

        double[][] inputs = new double[1][4];
        inputs[0][0] = 5.1;
        inputs[0][1] = 3.5;
        inputs[0][2] = 1.4;
        inputs[0][3] = 0.2;

        double[][] outputs = network.forwardPropagation(inputs);

        System.out.println(Arrays.toString(outputs[0]));
    }
}

这个示例代码可以将输入的四个特征值作为神经网络的输入，输出三个类别中每个类别的概率。你可以根据自己的需要进行调整和修改。