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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-bs008.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>
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<!-- navigation toc: --> <li><a href="._week41-bs042.html#the-derivative-of-the-logistic-funtion" style="font-size: 80%;">The derivative of the Logistic funtion</a></li>
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<!-- navigation toc: --> <li><a href="._week41-bs049.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-bs050.html#a-top-down-perspective-on-neural-networks" style="font-size: 80%;">A top-down perspective on Neural networks</a></li>
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<!-- navigation toc: --> <li><a href="._week41-bs056.html#3d-volumes-of-neurons" style="font-size: 80%;">3D volumes of neurons</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>
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>
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), as
discussed below. The figure here shows a typical situation of the
reduction of information in an image and is typical of what CNNs
actually end up doing.
<p>
<p>
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