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<a class="navbar-brand" href="week41-bs.html">Week 41 Constructing a Neural Network code, Tensor flow and start Convolutional Neural Networks</a>
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<!-- navigation toc: --> <li><a href="._week41-bs001.html#plan-for-week-41" style="font-size: 80%;">Plan for week 41</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs002.html#videos-on-neural-networks" style="font-size: 80%;">Videos on Neural Networks</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs003.html#review-of-the-back-propagation-algorithm" style="font-size: 80%;">Review of the back propagation algorithm</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs004.html#setting-up-the-back-propagation-algorithm" style="font-size: 80%;">Setting up the Back propagation algorithm</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs005.html#setting-up-a-multi-layer-perceptron-model-for-classification" style="font-size: 80%;">Setting up a Multi-layer perceptron model for classification</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs006.html#defining-the-cost-function" style="font-size: 80%;">Defining the cost function</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs007.html#example-binary-classification-problem" style="font-size: 80%;">Example: binary classification problem</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs008.html#the-softmax-function" style="font-size: 80%;">The Softmax function</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs009.html#developing-a-code-for-doing-neural-networks-with-back-propagation" style="font-size: 80%;">Developing a code for doing neural networks with back propagation</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs036.html#collect-and-pre-process-data" style="font-size: 80%;">Collect and pre-process data</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs011.html#train-and-test-datasets" style="font-size: 80%;">Train and test datasets</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs012.html#define-model-and-architecture" style="font-size: 80%;">Define model and architecture</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs013.html#layers" style="font-size: 80%;">Layers</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs014.html#weights-and-biases" style="font-size: 80%;">Weights and biases</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs015.html#feed-forward-pass" style="font-size: 80%;">Feed-forward pass</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs016.html#matrix-multiplications" style="font-size: 80%;">Matrix multiplications</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs017.html#choose-cost-function-and-optimizer" style="font-size: 80%;">Choose cost function and optimizer</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs018.html#optimizing-the-cost-function" style="font-size: 80%;">Optimizing the cost function</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs019.html#regularization" style="font-size: 80%;">Regularization</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs020.html#matrix-multiplication" style="font-size: 80%;">Matrix multiplication</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs021.html#improving-performance" style="font-size: 80%;">Improving performance</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs022.html#full-object-oriented-implementation" style="font-size: 80%;">Full object-oriented implementation</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs023.html#evaluate-model-performance-on-test-data" style="font-size: 80%;">Evaluate model performance on test data</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs024.html#adjust-hyperparameters" style="font-size: 80%;">Adjust hyperparameters</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs027.html#visualization" style="font-size: 80%;">Visualization</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs026.html#scikit-learn-implementation" style="font-size: 80%;">scikit-learn implementation</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs027.html#visualization" style="font-size: 80%;">Visualization</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs028.html#testing-our-code-for-the-xor-or-and-and-gates" style="font-size: 80%;">Testing our code for the XOR, OR and AND gates</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs029.html#the-and-and-xor-gates" style="font-size: 80%;">The AND and XOR Gates</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs030.html#representing-the-data-sets" style="font-size: 80%;">Representing the Data Sets</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs031.html#setting-up-the-neural-network" style="font-size: 80%;">Setting up the Neural Network</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs032.html#the-code-using-scikit-learn" style="font-size: 80%;">The Code using Scikit-Learn</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs033.html#building-neural-networks-in-tensorflow-and-keras" style="font-size: 80%;">Building neural networks in Tensorflow and Keras</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs034.html#tensorflow" style="font-size: 80%;">Tensorflow</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs035.html#using-keras" style="font-size: 80%;">Using Keras</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs036.html#collect-and-pre-process-data" style="font-size: 80%;">Collect and pre-process data</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs037.html#the-breast-cancer-data-now-with-keras" style="font-size: 80%;">The Breast Cancer Data, now with Keras</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs038.html#the-mathematics-of-neural-networks" style="font-size: 80%;">The Mathematics of Neural Networks</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs039.html#fine-tuning-neural-network-hyperparameters" style="font-size: 80%;">Fine-tuning neural network hyperparameters</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs040.html#hidden-layers" style="font-size: 80%;">Hidden layers</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs041.html#which-activation-function-should-i-use" style="font-size: 80%;">Which activation function should I use?</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs042.html#is-the-logistic-activation-function-sigmoid-our-choice" style="font-size: 80%;">Is the Logistic activation function (Sigmoid) our choice?</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs043.html#the-derivative-of-the-logistic-funtion" style="font-size: 80%;">The derivative of the Logistic funtion</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs044.html#the-relu-function-family" style="font-size: 80%;">The RELU function family</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs045.html#which-activation-function-should-we-use" style="font-size: 80%;">Which activation function should we use?</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs046.html#more-on-activation-functions-output-layers" style="font-size: 80%;">More on activation functions, output layers</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs047.html#batch-normalization" style="font-size: 80%;">Batch Normalization</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs048.html#dropout" style="font-size: 80%;">Dropout</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs049.html#gradient-clipping" style="font-size: 80%;">Gradient Clipping</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs050.html#a-very-nice-website-on-neural-networks" style="font-size: 80%;">A very nice website on Neural Networks</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs051.html#a-top-down-perspective-on-neural-networks" style="font-size: 80%;">A top-down perspective on Neural networks</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs052.html#limitations-of-supervised-learning-with-deep-networks" style="font-size: 80%;">Limitations of supervised learning with deep networks</a></li>
<!-- navigation toc: --> <li><a href="#overarching-views-a-personal-note" style="font-size: 80%;">Overarching Views, a personal note</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs054.html#using-automatic-differentiation" style="font-size: 80%;">Using Automatic differentiation</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs055.html#solving-odes-with-deep-learning" style="font-size: 80%;">Solving ODEs with Deep Learning</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs056.html#ordinary-differential-equations" style="font-size: 80%;">Ordinary Differential Equations</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs099.html#the-trial-solution" style="font-size: 80%;">The trial solution</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs058.html#minimization-process" style="font-size: 80%;">Minimization process</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs059.html#minimizing-the-cost-function-using-gradient-descent-and-automatic-differentiation" style="font-size: 80%;">Minimizing the cost function using gradient descent and automatic differentiation</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs060.html#example-exponential-decay" style="font-size: 80%;">Example: Exponential decay</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs061.html#the-function-to-solve-for" style="font-size: 80%;">The function to solve for</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs099.html#the-trial-solution" style="font-size: 80%;">The trial solution</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs063.html#setup-of-network" style="font-size: 80%;">Setup of Network</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs064.html#reformulating-the-problem" style="font-size: 80%;">Reformulating the problem</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs065.html#more-technicalities" style="font-size: 80%;">More technicalities</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs090.html#more-details" style="font-size: 80%;">More details</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs067.html#a-possible-implementation-of-a-neural-network" style="font-size: 80%;">A possible implementation of a neural network</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs068.html#technicalities" style="font-size: 80%;">Technicalities</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs069.html#final-technicalities-i" style="font-size: 80%;">Final technicalities I</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs070.html#final-technicalities-ii" style="font-size: 80%;">Final technicalities II</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs071.html#final-technicalities-iii" style="font-size: 80%;">Final technicalities III</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs072.html#final-technicalities-iv" style="font-size: 80%;">Final technicalities IV</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs073.html#back-propagation" style="font-size: 80%;">Back propagation</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs074.html#gradient-descent" style="font-size: 80%;">Gradient descent</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs075.html#the-code-for-solving-the-ode" style="font-size: 80%;">The code for solving the ODE</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs076.html#the-network-with-one-input-layer-specified-number-of-hidden-layers-and-one-output-layer" style="font-size: 80%;">The network with one input layer, specified number of hidden layers, and one output layer</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs077.html#example-population-growth" style="font-size: 80%;">Example: Population growth</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs078.html#setting-up-the-problem" style="font-size: 80%;">Setting up the problem</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs099.html#the-trial-solution" style="font-size: 80%;">The trial solution</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs080.html#the-program-using-autograd" style="font-size: 80%;">The program using Autograd</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs081.html#using-forward-euler-to-solve-the-ode" style="font-size: 80%;">Using forward Euler to solve the ODE</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs082.html#example-solving-the-one-dimensional-poisson-equation" style="font-size: 80%;">Example: Solving the one dimensional Poisson equation</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs083.html#the-specific-equation-to-solve-for" style="font-size: 80%;">The specific equation to solve for</a></li>
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<!-- navigation toc: --> <li><a href="._week41-bs090.html#more-details" style="font-size: 80%;">More details</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs091.html#example-the-diffusion-equation" style="font-size: 80%;">Example: The diffusion equation</a></li>
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<!-- navigation toc: --> <li><a href="._week41-bs093.html#setting-up-the-network-using-autograd" style="font-size: 80%;">Setting up the network using Autograd</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs094.html#setting-up-the-network-using-autograd-the-trial-solution" style="font-size: 80%;">Setting up the network using Autograd; The trial solution</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs095.html#why-the-jacobian" style="font-size: 80%;">Why the jacobian?</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs096.html#setting-up-the-network-using-autograd-the-full-program" style="font-size: 80%;">Setting up the network using Autograd; The full program</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs097.html#example-solving-the-wave-equation-with-neural-networks" style="font-size: 80%;">Example: Solving the wave equation with Neural Networks</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs098.html#the-problem-to-solve-for" style="font-size: 80%;">The problem to solve for</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs099.html#the-trial-solution" style="font-size: 80%;">The trial solution</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs100.html#the-analytical-solution" style="font-size: 80%;">The analytical solution</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs101.html#solving-the-wave-equation-the-full-program-using-autograd" style="font-size: 80%;">Solving the wave equation - the full program using Autograd</a></li>
<!-- navigation toc: --> <li><a href="._week41-bs102.html#resources-on-differential-equations-and-deep-learning" style="font-size: 80%;">Resources on differential equations and deep learning</a></li>
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<h2 id="overarching-views-a-personal-note" class="anchor">Overarching Views, a personal note </h2>
<p>The author of these lecture notes has an overarching take on many of
the machine learning algorithms we discuss here.
</p>
<p>If we wish to understand complex systems, we need to find some
effective degrees of freedom or features that we find essential,
simply in order to reduce the complexity of the systems we are
studying. This leads, in one way or the other to dimensionality
reductions. Most of the Machine Learning methods we encounter deal
with this, whether we opt for a principal component analysis, or
clustering, or convolutional neural networks, or Ridge or Lasso
regression or random forest, yes, perhaps most machine learning
methods at large.
</p>
<p>For neural networks and our previous discussion, we have seen that we
in essence end up with matrix-matrix and matrix-vector
multiplications. In all cases, our matrices are dense ones, and the
more data we deal with the larger the dimensionalities of the matrices
and vectors. How can we reduce such dimensionalities? One possible
answer is offered by <b>convolutional neural networks</b> (CNN), to be discussed next week.
</p>
<p>
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