网上已经有很多人对这个练习有过实践和经验分享了，参考了一些别人的代码，都差不多，基本上也只能这样写了，只有pool时有点区别，不过感觉速度并不会差太多。
代码如下。
cnnConvolve.m
function convolvedFeatures = cnnConvolve(patchDim, numFeatures, images, W, b, ZCAWhite, meanPatch)
%cnnConvolve Returns the convolution of the features given by W and b with
%the given images
%
% Parameters:
% patchDim - patch (feature) dimension
% numFeatures - number of features
% images - large images to convolve with, matrix in the form
% images(r, c, channel, image number)
% W, b - W, b for features from the sparse autoencoder
% ZCAWhite, meanPatch - ZCAWhitening and meanPatch matrices used for
% preprocessing
%
% Returns:
% convolvedFeatures - matrix of convolved features in the form
% convolvedFeatures(featureNum, imageNum, imageRow, imageCol)numImages = size(images, 4);
imageDim = size(images, 1);
imageChannels = size(images, 3);convolvedFeatures = zeros(numFeatures, numImages, imageDim - patchDim + 1, imageDim - patchDim + 1);% Instructions:
% Convolve every feature with every large image here to produce the
% numFeatures x numImages x (imageDim - patchDim + 1) x (imageDim - patchDim + 1)
% matrix convolvedFeatures, such that
% convolvedFeatures(featureNum, imageNum, imageRow, imageCol) is the
% value of the convolved featureNum feature for the imageNum image over
% the region (imageRow, imageCol) to (imageRow + patchDim - 1, imageCol + patchDim - 1)
%
% Expected running times:
% Convolving with 100 images should take less than 3 minutes
% Convolving with 5000 images should take around an hour
% (So to save time when testing, you should convolve with less images, as
% described earlier)%% -------------------- YOUR CODE HERE --------------------
% Precompute the matrices that will be used during the convolution. Recall
% that you need to take into account the whitening and mean subtraction
% steps%先reshape为64*64*3行 imgNum列的输入图像矩阵
%images = reshape(images, imageDim * imageDim * imageChannels, numImages);WT = W * ZCAWhite; %400*192
b = b - WT * meanPatch; %400*1
patchSize = patchDim * patchDim; % --------------------------------------------------------convolvedFeatures = zeros(numFeatures, numImages, imageDim - patchDim + 1, imageDim - patchDim + 1);
for imageNum = 1:numImagesfor featureNum = 1:numFeatures% convolution of image with feature matrix for each channelconvolvedImage = zeros(imageDim - patchDim + 1, imageDim - patchDim + 1);for channel = 1:3% Obtain the feature (patchDim x patchDim) needed during the convolution% ---- YOUR CODE HERE ----feature = reshape(WT(featureNum,(channel-1)*patchSize+1:channel*patchSize), patchDim, patchDim); % ------------------------ % Flip the feature matrix because of the definition of convolution, as explained laterfeature = rot90(squeeze(feature),2);% Obtain the imageim = squeeze(images(:, :, channel, imageNum));% Convolve "feature" with "im", adding the result to convolvedImage% be sure to do a 'valid' convolution% ---- YOUR CODE HERE ----convolvedImage = convolvedImage + conv2(im, feature, 'valid'); % ------------------------end% Subtract the bias unit (correcting for the mean subtraction as well)% Then, apply the sigmoid function to get the hidden activation% ---- YOUR CODE HERE ----convolvedImage = sigmoid(convolvedImage + b(featureNum)); % ------------------------% The convolved feature is the sum of the convolved values for all channelsconvolvedFeatures(featureNum, imageNum, :, :) = convolvedImage;end
endendfunction sigm = sigmoid(x)sigm = 1 ./ (1 + exp(-x));
endcnnPool.m
function pooledFeatures = cnnPool(poolDim, convolvedFeatures)
%cnnPool Pools the given convolved features
%
% Parameters:
% poolDim - dimension of pooling region
% convolvedFeatures - convolved features to pool (as given by cnnConvolve)
% convolvedFeatures(featureNum, imageNum, imageRow, imageCol)
%
% Returns:
% pooledFeatures - matrix of pooled features in the form
% pooledFeatures(featureNum, imageNum, poolRow, poolCol)
% numImages = size(convolvedFeatures, 2);
numFeatures = size(convolvedFeatures, 1);
convolvedDim = size(convolvedFeatures, 3);pooledFeatures = zeros(numFeatures, numImages, floor(convolvedDim / poolDim), floor(convolvedDim / poolDim));% -------------------- YOUR CODE HERE --------------------
% Instructions:
% Now pool the convolved features in regions of poolDim x poolDim,
% to obtain the
% numFeatures x numImages x (convolvedDim/poolDim) x (convolvedDim/poolDim)
% matrix pooledFeatures, such that
% pooledFeatures(featureNum, imageNum, poolRow, poolCol) is the
% value of the featureNum feature for the imageNum image pooled over the
% corresponding (poolRow, poolCol) pooling region
% (see http://ufldl/wiki/index.php/Pooling )
%
% Use mean pooling here.
% -------------------- YOUR CODE HERE --------------------
poolRow = floor(convolvedDim / poolDim);
for featureNum = 1:numFeaturesfor imgNum = 1:numImagesfor row = 1:poolRowfor col = 1:poolRowpooledFeatures(featureNum, imgNum, row, col) = mean(mean(convolvedFeatures(featureNum, imgNum, (row-1)*poolDim + 1:row*poolDim, (col-1)*poolDim + 1:col*poolDim)));endendend
endcnnExercise.m
%% CS294A/CS294W Convolutional Neural Networks Exercise% Instructions
% ------------
%
% This file contains code that helps you get started on the
% convolutional neural networks exercise. In this exercise, you will only
% need to modify cnnConvolve.m and cnnPool.m. You will not need to modify
% this file.%%======================================================================
%% STEP 0: Initialization
% Here we initialize some parameters used for the exercise.imageDim = 64; % image dimension
imageChannels = 3; % number of channels (rgb, so 3)patchDim = 8; % patch dimension
numPatches = 50000; % number of patchesvisibleSize = patchDim * patchDim * imageChannels; % number of input units
outputSize = visibleSize; % number of output units
hiddenSize = 400; % number of hidden units epsilon = 0.1; % epsilon for ZCA whiteningpoolDim = 19; % dimension of pooling region%%======================================================================
%% STEP 1: Train a sparse autoencoder (with a linear decoder) to learn
% features from color patches. If you have completed the linear decoder
% execise, use the features that you have obtained from that exercise,
% loading them into optTheta. Recall that we have to keep around the
% parameters used in whitening (i.e., the ZCA whitening matrix and the
% meanPatch)% --------------------------- YOUR CODE HERE --------------------------
% Train the sparse autoencoder and fill the following variables with
% the optimal parameters:
STL10Features = load('STL10Features.mat');optTheta = STL10Features.optTheta ;
ZCAWhite = STL10Features.ZCAWhite;
meanPatch = STL10Features.meanPatch;
% --------------------------------------------------------------------% Display and check to see that the features look good
W = reshape(optTheta(1:visibleSize * hiddenSize), hiddenSize, visibleSize);
b = optTheta(2*hiddenSize*visibleSize+1:2*hiddenSize*visibleSize+hiddenSize);displayColorNetwork( (W*ZCAWhite)');%%====================================================================== %% STEP 2: Implement and test convolution and pooling % In this step, you will implement convolution and pooling, and test them % on a small part of the data set to ensure that you have implemented % these two functions correctly. In the next step, you will actually % convolve and pool the features with the STL10 images.%% STEP 2a: Implement convolution % Implement convolution in the function cnnConvolve in cnnConvolve.m% Note that we have to preprocess the images in the exact same way % we preprocessed the patches before we can obtain the feature activations.load stlTrainSubset.mat % loads numTrainImages, trainImages, trainLabels%% Use only the first 8 images for testing convImages = trainImages(:, :, :, 1:8); % NOTE: Implement cnnConvolve in cnnConvolve.m first! convolvedFeatures = cnnConvolve(patchDim, hiddenSize, convImages, W, b, ZCAWhite, meanPatch);%% STEP 2b: Checking your convolution % To ensure that you have convolved the features correctly, we have % provided some code to compare the results of your convolution with % activations from the sparse autoencoder% For 1000 random points for i = 1:1000 featureNum = randi([1, hiddenSize]);imageNum = randi([1, 8]);imageRow = randi([1, imageDim - patchDim + 1]);imageCol = randi([1, imageDim - patchDim + 1]); patch = convImages(imageRow:imageRow + patchDim - 1, imageCol:imageCol + patchDim - 1, :, imageNum);patch = patch(:); patch = patch - meanPatch;patch = ZCAWhite * patch;features = feedForwardAutoencoder(optTheta, hiddenSize, visibleSize, patch); if abs(features(featureNum, 1) - convolvedFeatures(featureNum, imageNum, imageRow, imageCol)) > 1e-9fprintf('Convolved feature does not match activation from autoencoder\n');fprintf('Feature Number : %d\n', featureNum);fprintf('Image Number : %d\n', imageNum);fprintf('Image Row : %d\n', imageRow);fprintf('Image Column : %d\n', imageCol);fprintf('Convolved feature : %0.5f\n', convolvedFeatures(featureNum, imageNum, imageRow, imageCol));fprintf('Sparse AE feature : %0.5f\n', features(featureNum, 1)); error('Convolved feature does not match activation from autoencoder');end
enddisp('Congratulations! Your convolution code passed the test.');%% STEP 2c: Implement pooling
% Implement pooling in the function cnnPool in cnnPool.m% NOTE: Implement cnnPool in cnnPool.m first!
pooledFeatures = cnnPool(poolDim, convolvedFeatures);%% STEP 2d: Checking your pooling
% To ensure that you have implemented pooling, we will use your pooling
% function to pool over a test matrix and check the results.testMatrix = reshape(1:64, 8, 8);
expectedMatrix = [mean(mean(testMatrix(1:4, 1:4))) mean(mean(testMatrix(1:4, 5:8))); ...mean(mean(testMatrix(5:8, 1:4))) mean(mean(testMatrix(5:8, 5:8))); ];testMatrix = reshape(testMatrix, 1, 1, 8, 8);pooledFeatures = squeeze(cnnPool(4, testMatrix));if ~isequal(pooledFeatures, expectedMatrix)disp('Pooling incorrect');disp('Expected');disp(expectedMatrix);disp('Got');disp(pooledFeatures);
elsedisp('Congratulations! Your pooling code passed the test.');
end%%======================================================================
%% STEP 3: Convolve and pool with the dataset
% In this step, you will convolve each of the features you learned with
% the full large images to obtain the convolved features. You will then
% pool the convolved features to obtain the pooled features for
% classification.
%
% Because the convolved features matrix is very large, we will do the
% convolution and pooling 50 features at a time to avoid running out of
% memory. Reduce this number if necessarystepSize = 50;
assert(mod(hiddenSize, stepSize) == 0, 'stepSize should divide hiddenSize');load stlTrainSubset.mat % loads numTrainImages, trainImages, trainLabels
load stlTestSubset.mat % loads numTestImages, testImages, testLabelspooledFeaturesTrain = zeros(hiddenSize, numTrainImages, ...floor((imageDim - patchDim + 1) / poolDim), ...floor((imageDim - patchDim + 1) / poolDim) );
pooledFeaturesTest = zeros(hiddenSize, numTestImages, ...floor((imageDim - patchDim + 1) / poolDim), ...floor((imageDim - patchDim + 1) / poolDim) );tic();for convPart = 1:(hiddenSize / stepSize)featureStart = (convPart - 1) * stepSize + 1;%1/51/101/151...featureEnd = convPart * stepSize; %50/100/150/200...fprintf('Step %d: features %d to %d\n', convPart, featureStart, featureEnd); Wt = W(featureStart:featureEnd, :); %1:50 * 192bt = b(featureStart:featureEnd); % 1;50 * 1fprintf('Convolving and pooling train images\n');convolvedFeaturesThis = cnnConvolve(patchDim, stepSize, ...trainImages, Wt, bt, ZCAWhite, meanPatch);pooledFeaturesThis = cnnPool(poolDim, convolvedFeaturesThis);pooledFeaturesTrain(featureStart:featureEnd, :, :, :) = pooledFeaturesThis; toc();clear convolvedFeaturesThis pooledFeaturesThis;fprintf('Convolving and pooling test images\n');convolvedFeaturesThis = cnnConvolve(patchDim, stepSize, ...testImages, Wt, bt, ZCAWhite, meanPatch);pooledFeaturesThis = cnnPool(poolDim, convolvedFeaturesThis);pooledFeaturesTest(featureStart:featureEnd, :, :, :) = pooledFeaturesThis; toc();clear convolvedFeaturesThis pooledFeaturesThis;end% You might want to save the pooled features since convolution and pooling takes a long time
save('cnnPooledFeatures.mat', 'pooledFeaturesTrain', 'pooledFeaturesTest');
toc();%%======================================================================
%% STEP 4: Use pooled features for classification
% Now, you will use your pooled features to train a softmax classifier,
% using softmaxTrain from the softmax exercise.
% Training the softmax classifer for 1000 iterations should take less than
% 10 minutes.% Add the path to your softmax solution, if necessary
% addpath /path/to/solution/% Setup parameters for softmax
softmaxLambda = 1e-4;
numClasses = 4;
% Reshape the pooledFeatures to form an input vector for softmax
softmaxX = permute(pooledFeaturesTrain, [1 3 4 2]);
softmaxX = reshape(softmaxX, numel(pooledFeaturesTrain) / numTrainImages,...numTrainImages);
softmaxY = trainLabels;options = struct;
options.maxIter = 200;
softmaxModel = softmaxTrain(numel(pooledFeaturesTrain) / numTrainImages,...numClasses, softmaxLambda, softmaxX, softmaxY, options);%%======================================================================
%% STEP 5: Test classifer
% Now you will test your trained classifer against the test imagessoftmaxX = permute(pooledFeaturesTest, [1 3 4 2]);
softmaxX = reshape(softmaxX, numel(pooledFeaturesTest) / numTestImages, numTestImages);
softmaxY = testLabels;[pred] = softmaxPredict(softmaxModel, softmaxX);
acc = (pred(:) == softmaxY(:));
acc = sum(acc) / size(acc, 1);
fprintf('Accuracy: %2.3f%%\n', acc * 100);% You should expect to get an accuracy of around 80% on the test images.运行结果：
cnnExercise
Congratulations! Your convolution code passed the test.
Congratulations! Your pooling code passed the test.
Step 1: features 1 to 50
Convolving and pooling train images
时间已过 43.559439 秒。
Convolving and pooling test images
时间已过 113.963827 秒。
Step 2: features 51 to 100
Convolving and pooling train images
时间已过 159.439742 秒。
Convolving and pooling test images
时间已过 233.019103 秒。
Step 3: features 101 to 150
Convolving and pooling train images
时间已过 277.864539 秒。
Convolving and pooling test images
时间已过 346.115529 秒。
Step 4: features 151 to 200
Convolving and pooling train images
时间已过 389.081485 秒。
Convolving and pooling test images
时间已过 456.220277 秒。
Step 5: features 201 to 250
Convolving and pooling train images
时间已过 497.692379 秒。
Convolving and pooling test images
时间已过 565.704817 秒。
Step 6: features 251 to 300
Convolving and pooling train images
时间已过 607.816857 秒。
Convolving and pooling test images
时间已过 675.201399 秒。
Step 7: features 301 to 350
Convolving and pooling train images
时间已过 716.899438 秒。
Convolving and pooling test images
时间已过 784.383367 秒。
Step 8: features 351 to 400
Convolving and pooling train images
时间已过 826.690455 秒。
Convolving and pooling test images
时间已过 897.530101 秒。
时间已过 905.283274 秒。
Iteration FunEvals Step Length Function Val Opt Cond
1 4 7.24380e+00 1.27112e+00 3.62697e+01
2 5 1.00000e+00 1.09817e+00 2.96941e+01
3 6 1.00000e+00 9.93335e-01 3.33820e+01
4 7 1.00000e+00 8.66513e-01 1.97885e+01
5 8 1.00000e+00 8.34927e-01 1.37416e+01
6 9 1.00000e+00 8.21185e-01 3.91644e+00
7 10 1.00000e+00 8.15098e-01 4.33652e+00
8 11 1.00000e+00 8.05982e-01 5.64183e+00
9 12 1.00000e+00 7.79885e-01 4.87652e+00
10 13 1.00000e+00 6.73033e-01 2.92103e+00
11 14 1.00000e+00 6.18085e-01 1.56961e+01
…
…
…
93 96 1.00000e+00 4.69884e-01 2.57284e-04
94 97 1.00000e+00 4.69884e-01 5.01674e-04
95 98 1.00000e+00 4.69884e-01 3.96913e-04
Function Value changing by less than TolX
Accuracy: 80.531%
前面稀疏自编码器直接用之前训练好的参数，然后卷积和池化花的时间比较久，不过对池化以后的特征进行softmax回归训练的速度相当快，10秒钟就训练完并收敛达到目标loss，最后准确率80%，也和标准答案一模一样~