DBN模型matlab代码

DBN（Deep Belief Network）是一种深度学习模型，它由多个受限玻尔兹曼机（Restricted Boltzmann Machine，RBM）组成。DBN模型在机器学习中被广泛应用于特征学习和生成模型等任务。

以下是一个使用Matlab实现DBN模型的简单示例代码：

% 导入数据
data = load('data.mat');
trainData = data.trainData;
testData = data.testData;

% 设置DBN模型参数
numLayers = 3; % DBN的层数
hiddenSizes = [100, 200, 300]; % 每一层的隐藏单元数量

% 训练每一层的RBM
rbmLayers = cell(1, numLayers);
for i = 1:numLayers
    if i == 1
        inputSize = size(trainData, 2);
        rbmLayers{i} = trainRBM(trainData, hiddenSizes(i));
    else
        inputSize = hiddenSizes(i-1);
        rbmLayers{i} = trainRBM(hiddenActivations, hiddenSizes(i));
    end
    
    hiddenActivations = sigmoid(bsxfun(@plus, trainData * rbmLayers{i}.Weights, rbmLayers{i}.HiddenBiases));
    trainData = hiddenActivations;
end

% Fine-tuning：使用反向传播算法微调DBN模型
dbn = fineTuneDBN(rbmLayers, trainData, labels);

% 在测试集上进行预测
predictedLabels = predict(dbn, testData);

% 计算准确率
accuracy = sum(predictedLabels == trueLabels) / numel(trueLabels);

% 辅助函数：训练RBM
function rbm = trainRBM(data, hiddenSize)
    numEpochs = 100; % 训练轮数
    learningRate = 0.1; % 学习率
    
    numVisibleUnits = size(data, 2);
    rbm = struct();
    rbm.Weights = randn(numVisibleUnits, hiddenSize);
    rbm.VisibleBiases = zeros(1, numVisibleUnits);
    rbm.HiddenBiases = zeros(1, hiddenSize);
    
    for epoch = 1:numEpochs
        % 正向传播
        hiddenActivations = sigmoid(bsxfun(@plus, data * rbm.Weights, rbm.HiddenBiases));
        hiddenStates = hiddenActivations > rand(size(hiddenActivations));
        
        % 反向传播
        visibleActivations = sigmoid(bsxfun(@plus, hiddenStates * rbm.Weights', rbm.VisibleBiases));
        visibleStates = visibleActivations > rand(size(visibleActivations));
        
        % 更新权重和偏置
        deltaWeights = learningRate * (data' * hiddenActivations - visibleStates' * hiddenStates) / size(data, 1);
        deltaVisibleBiases = learningRate * sum(data - visibleStates) / size(data, 1);
        deltaHiddenBiases = learningRate * sum(hiddenActivations - hiddenStates) / size(data, 1);
        
        rbm.Weights = rbm.Weights + deltaWeights;
        rbm.VisibleBiases = rbm.VisibleBiases + deltaVisibleBiases;
        rbm.HiddenBiases = rbm.HiddenBiases + deltaHiddenBiases;
    end
end

% 辅助函数：使用反向传播算法微调DBN模型
function dbn = fineTuneDBN(rbmLayers, trainData, labels)
    numClasses = numel(unique(labels));
    dbn = struct();
    dbn.rbmLayers = rbmLayers;
    dbn.Weights = cell(1, numel(rbmLayers));
    dbn.Biases = cell(1, numel(rbmLayers));
    
    % 初始化权重和偏置
    for i = 1:numel(rbmLayers)
        if i == 1
            inputSize = size(trainData, 2);
        else
            inputSize = rbmLayers{i-1}.hiddenSize;
        end
        
        dbn.Weights{i} = randn(inputSize, rbmLayers{i}.hiddenSize);
        dbn.Biases{i} = zeros(1, rbmLayers{i}.hiddenSize);
    end
    
    % Fine-tuning
    options = optimset('MaxIter', 100);
    dbn = fminunc(@(params) crossEntropyCost(params, trainData, labels, numClasses, dbn), [dbn.Weights(:); dbn.Biases(:)], options);
    
    % 辅助函数：计算交叉熵损失函数
    function cost = crossEntropyCost(params, data, labels, numClasses, dbn)
        numLayers = numel(dbn.rbmLayers);
        dbn.Weights = reshape(params(1:numel(dbn.Weights)), size(dbn.Weights));
        dbn.Biases = reshape(params(numel(dbn.Weights)+1:end), size(dbn.Biases));
        
        % 正向传播
        activations = cell(1, numLayers+1);
        activations{1} = data;
        for i = 1:numLayers
            activations{i+1} = sigmoid(bsxfun(@plus, activations{i} * dbn.Weights{i}, dbn.Biases{i}));
        end
        
        % 计算交叉熵损失
        output = softmax(bsxfun(@plus, activations{end} * dbn.Weights{end}, dbn.Biases{end}));
        cost = -sum(sum(labels .* log(output))) / size(data, 1);
    end
end

% 辅助函数：sigmoid函数
function output = sigmoid(x)
    output = 1 ./ (1 + exp(-x));
end

% 辅助函数：softmax函数
function output = softmax(x)
    output = exp(x) ./ sum(exp(x), 2);
end

请注意，这只是一个简单的示例代码，实际应用中可能需要根据具体问题进行适当的修改和调整。另外，为了运行该代码，你需要提供训练数据和测试数据，并将其保存为`data.mat`文件。