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<a class="navbar-brand" href="NeuralNet-bs.html">Data Analysis and Machine Learning: Neural networks, from the simple perceptron to deep learning and convolutional networks</a>
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<!-- navigation toc: --> <li><a href="._NeuralNet-bs001.html#___sec0" style="font-size: 80%;"><b>Neural networks</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs002.html#___sec1" style="font-size: 80%;"><b>Artificial neurons</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs003.html#___sec2" style="font-size: 80%;"><b>Neural network types</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs004.html#___sec3" style="font-size: 80%;"><b>Feed-forward neural networks</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs005.html#___sec4" style="font-size: 80%;"><b>Convolutional Neural Network</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs006.html#___sec5" style="font-size: 80%;"><b>Recurrent neural networks</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs007.html#___sec6" style="font-size: 80%;"><b>Other types of networks</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs008.html#___sec7" style="font-size: 80%;"><b>Multilayer perceptrons</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs009.html#___sec8" style="font-size: 80%;"><b>Why multilayer perceptrons?</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs010.html#___sec9" style="font-size: 80%;"><b>Mathematical model</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs011.html#___sec10" style="font-size: 80%;"><b>Mathematical model</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs012.html#___sec11" style="font-size: 80%;"><b>Mathematical model</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs013.html#___sec12" style="font-size: 80%;"><b>Mathematical model</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs014.html#___sec13" style="font-size: 80%;"><b>Mathematical model</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs015.html#___sec14" style="font-size: 80%;">&nbsp;&nbsp;&nbsp;Matrix-vector notation</a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs016.html#___sec15" style="font-size: 80%;">&nbsp;&nbsp;&nbsp;Matrix-vector notation and activation</a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs017.html#___sec16" style="font-size: 80%;">&nbsp;&nbsp;&nbsp;Activation functions</a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs018.html#___sec17" style="font-size: 80%;">&nbsp;&nbsp;&nbsp;Activation functions, Logistic and Hyperbolic ones</a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs019.html#___sec18" style="font-size: 80%;">&nbsp;&nbsp;&nbsp;Relevance</a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs020.html#___sec19" style="font-size: 80%;"><b>The multilayer perceptron (MLP)</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs021.html#___sec20" style="font-size: 80%;"><b>From one to many layers, the universal approximation theorem</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs022.html#___sec21" style="font-size: 80%;"><b>Deriving the back propagation code for a multilayer perceptron model</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs023.html#___sec22" style="font-size: 80%;"><b>Definitions</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs024.html#___sec23" style="font-size: 80%;"><b>Derivatives and the chain rule</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs025.html#___sec24" style="font-size: 80%;"><b>Derivative of the cost function</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs026.html#___sec25" style="font-size: 80%;"><b>Bringing it together, first back propagation equation</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs027.html#___sec26" style="font-size: 80%;"><b>Derivatives in terms of \( z_j^L \)</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs028.html#___sec27" style="font-size: 80%;"><b>Bringing it together</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs029.html#___sec28" style="font-size: 80%;"><b>Final back propagating equation</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs030.html#___sec29" style="font-size: 80%;"><b>Setting up the Back propagation algorithm</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs031.html#___sec30" style="font-size: 80%;"><b>Setting up a Multi-layer perceptron model for classification</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs032.html#___sec31" style="font-size: 80%;"><b>Defining the cost function</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs033.html#___sec32" style="font-size: 80%;"><b>Example: binary classification problem</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs034.html#___sec33" style="font-size: 80%;"><b>The Softmax function</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs035.html#___sec34" style="font-size: 80%;"><b>Developing a code for doing neural networks with back propagation</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs036.html#___sec35" style="font-size: 80%;"><b>Collect and pre-process data</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs037.html#___sec36" style="font-size: 80%;"><b>Train and test datasets</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs038.html#___sec37" style="font-size: 80%;"><b>Define model and architecture</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs039.html#___sec38" style="font-size: 80%;"><b>Layers</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs040.html#___sec39" style="font-size: 80%;"><b>Weights and biases</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs041.html#___sec40" style="font-size: 80%;"><b>Feed-forward pass</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs042.html#___sec41" style="font-size: 80%;"><b>Matrix multiplications</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs043.html#___sec42" style="font-size: 80%;"><b>Choose cost function and optimizer</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs044.html#___sec43" style="font-size: 80%;"><b>Optimizing the cost function</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs045.html#___sec44" style="font-size: 80%;"><b>Regularization</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs046.html#___sec45" style="font-size: 80%;"><b>Matrix multiplication</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs047.html#___sec46" style="font-size: 80%;"><b>Improving performance</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs048.html#___sec47" style="font-size: 80%;"><b>Full object-oriented implementation</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs049.html#___sec48" style="font-size: 80%;"><b>Evaluate model performance on test data</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs050.html#___sec49" style="font-size: 80%;"><b>Adjust hyperparameters</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs051.html#___sec50" style="font-size: 80%;"><b>Visualization</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs052.html#___sec51" style="font-size: 80%;"><b>scikit-learn implementation</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs053.html#___sec52" style="font-size: 80%;"><b>Visualization</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs054.html#___sec53" style="font-size: 80%;"><b>Building neural networks in Tensorflow and Keras</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs055.html#___sec54" style="font-size: 80%;"><b>Tensorflow</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs056.html#___sec55" style="font-size: 80%;"><b>Collect and pre-process data</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs057.html#___sec56" style="font-size: 80%;"><b>Using TensorFlow backend</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs058.html#___sec57" style="font-size: 80%;"><b>Optimizing and using gradient descent</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs059.html#___sec58" style="font-size: 80%;"><b>Using Keras</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs060.html#___sec59" style="font-size: 80%;"><b>Which activation function should I use?</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs061.html#___sec60" style="font-size: 80%;"><b>Is the Logistic activation function (Sigmoid) our choice?</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs062.html#___sec61" style="font-size: 80%;"><b>The derivative of the Logistic funtion</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs063.html#___sec62" style="font-size: 80%;"><b>The RELU function family</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs064.html#___sec63" style="font-size: 80%;"><b>Which activation function should we use?</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs065.html#___sec64" style="font-size: 80%;"><b>A top-down perspective on Neural networks</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs066.html#___sec65" style="font-size: 80%;"><b>Limitations of supervised learning with deep networks</b></a></li>
<!-- navigation toc: --> <li><a href="#___sec66" style="font-size: 80%;"><b>Convolutional Neural Networks (recognizing images)</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs068.html#___sec67" style="font-size: 80%;"><b>Regular NNs dont scale well to full images</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs069.html#___sec68" style="font-size: 80%;"><b>3D volumes of neurons</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs070.html#___sec69" style="font-size: 80%;"><b>Layers used to build CNNs</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs071.html#___sec70" style="font-size: 80%;"><b>Transforming images</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs072.html#___sec71" style="font-size: 80%;"><b>CNNs in brief</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs073.html#___sec72" style="font-size: 80%;"><b>CNNs in more detail, building convolutional neural networks in Tensorflow and Keras</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs074.html#___sec73" style="font-size: 80%;"><b>Setting it up</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs075.html#___sec74" style="font-size: 80%;"><b>The MNIST dataset again</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs076.html#___sec75" style="font-size: 80%;"><b>Strong correlations</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs077.html#___sec76" style="font-size: 80%;"><b>Layers of a CNN</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs078.html#___sec77" style="font-size: 80%;"><b>Systematic reduction</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs079.html#___sec78" style="font-size: 80%;"><b>Prerequisites: Collect and pre-process data</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs080.html#___sec79" style="font-size: 80%;"><b>Importing Keras and Tensorflow</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs081.html#___sec80" style="font-size: 80%;"><b>Using TensorFlow backend</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs082.html#___sec81" style="font-size: 80%;"><b>Train the model</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs083.html#___sec82" style="font-size: 80%;"><b>Visualizing the results</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs084.html#___sec83" style="font-size: 80%;"><b>Running with Keras</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs085.html#___sec84" style="font-size: 80%;"><b>Final part</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs086.html#___sec85" style="font-size: 80%;"><b>Final visualization</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs087.html#___sec86" style="font-size: 80%;"><b>Fun links</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs088.html#___sec87" style="font-size: 80%;"><b>Applications: solving ordinary differential equations with Neural Networks</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs089.html#___sec88" style="font-size: 80%;"><b>Trial solution</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs090.html#___sec89" style="font-size: 80%;"><b>More details</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs091.html#___sec90" style="font-size: 80%;"><b>Reformulating the problem</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs092.html#___sec91" style="font-size: 80%;"><b>Estimating errors</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs093.html#___sec92" style="font-size: 80%;"><b>Creating a simple Deep Neural Net</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs094.html#___sec93" style="font-size: 80%;"><b>Setting up the code, feed forward part</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs095.html#___sec94" style="font-size: 80%;"><b>Backpropagation</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs096.html#___sec95" style="font-size: 80%;"><b>Gradient Descent</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs097.html#___sec96" style="font-size: 80%;"><b>More on GD and cost function</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs098.html#___sec97" style="font-size: 80%;"><b>An implementation of a Deep Neural Network</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs099.html#___sec98" style="font-size: 80%;"><b>The final parts of the code</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs100.html#___sec99" style="font-size: 80%;"><b>And adding Back propagation</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs101.html#___sec100" style="font-size: 80%;"><b>Solving the ODE</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs102.html#___sec101" style="font-size: 80%;"><b>Using neural network</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs103.html#___sec102" style="font-size: 80%;"><b>Using a deep neural network</b></a></li>
<!-- navigation toc: --> <li><a href="._NeuralNet-bs104.html#___sec103" style="font-size: 80%;"><b>Wrapping it up</b></a></li>
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<h2 id="___sec66" class="anchor">Convolutional Neural Networks (recognizing images) </h2>
<p>
Convolutional Neural Networks (CNN) are very similar to ordinary Neural Networks.
<p>
They are made up of neurons that have learnable weights and
biases. Each neuron receives some inputs, performs a dot product and
optionally follows it with a non-linearity. The whole network still
expresses a single differentiable score function: from the raw image
pixels on one end to class scores at the other. And they still have a
loss function (for example Softmax) on the last (fully-connected) layer
and all the tips/tricks we developed for learning regular Neural
Networks still apply (back propagation, gradient descent etc etc).
<p>
What is the difference? <b>CNN architectures make the explicit assumption that
the inputs are images, which allows us to encode certain properties
into the architecture. These then make the forward function more
efficient to implement and vastly reduce the amount of parameters in
the network.</b>
<p>
Here we provide only a superficial overview, for the more interested, we recommend highly the course
<a href="https://www.uio.no/studier/emner/matnat/ifi/IN5400/index-eng.html" target="_self">IN5400 &#8211; Machine Learning for Image Analysis</a>
and the slides of <a href="http://cs231n.github.io/convolutional-networks/" target="_self">CS231</a>.
<p>
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