Deep Neural Networks


Training Your First Neural Network
12m 40s
Improving Accuracy
8m 4s
Start course
1h 3m

Machine learning is a hot topic these days and Google has been one of the biggest newsmakers. Google’s machine learning is being used behind the scenes every day by millions of people. When you search for an image on the web or use Google Translate on foreign language text or use voice dictation on your Android phone, you’re using machine learning. Now Google has launched AI Platform to give its customers the power to train their own neural networks.

This is a hands-on course where you can follow along with the demos using your own Google Cloud account or a trial account.

Learning Objectives

  • Describe how an artificial neural network functions
  • Run a simple TensorFlow program
  • Train a model using a distributed cluster on AI Platform
  • Increase prediction accuracy using feature engineering and hyperparameter tuning
  • Deploy a trained model on AI Platform to make predictions with new data



  • December 20, 2020: Completely revamped the course due to Google AI Platform replacing Cloud ML Engine and the release of TensorFlow 2.
  • Nov. 16, 2018: Updated 90% of the lessons due to major changes in TensorFlow and Google Cloud ML Engine. All of the demos and code walkthroughs were completely redone.

In the last lesson, we created a deep neural network. So, what makes a deep neural network different from a regular one, and why would you need to use it? Although “deep learning” sounds like it must be a complex, almost mystical concept, really it just means that the neural network has more than three layers, like this.

The layers in between the outside ones are called hidden layers because their inputs and outputs are not visible. Hidden layers are useful because they allow the network to combine features to recognize higher-level patterns.

Returning to our home value estimator, suppose that in some neighborhoods, older homes are more highly valued than newer homes, but in other neighborhoods, newer homes are more highly valued than older homes. In a two-layer neural network, all of the features are independent from each other, so there’s no way to combine a home’s age and its neighborhood to determine how much the value should increase or decrease.

Well, actually there is a way, but it requires a lot of insight on the part of the person building the network. You could create new features that are combinations of the original features and include them at the input layer. We’ll go over this approach in another lesson.

The great thing about deep networks is that they can often discover these relationships for you. That’s because each node in a hidden layer combines the outputs from all of the nodes in the previous layer in different ways.

The result is that a node in a hidden layer can potentially become a “feature detector”. There’s a nice illustration in this research paper. This shows a neural network that’s trying to detect a face in an image. In the first layer, it detects edges. In the second layer, it combines these edges to detect simple shapes. In the third layer, it combines the simple shapes to detect facial shapes. If you had a network with no hidden layers, then it would have to try to detect a face based on only the individual pixels in the image, which would be much more difficult.

The beauty of this is that it discovers these features itself without any guidance from the person building the neural network. This is what can make deep learning seem almost magical.

Now, going back to the iris classifier, let’s have a look at its hidden layers. There are 10 nodes in each of the two layers.

So, how much of a difference do the hidden layers make? Well, the easiest way to find out is to remove the hidden layers and see how much lower the accuracy is. I’ll just comment the lines out. Now let’s run it again.

The accuracy is much lower. So it looks like the hidden layers did make a big difference.

Before we move on, you should undo the changes you made to the script and save it again.

And that’s it for this lesson.

About the Author
Learning Paths

Guy launched his first training website in 1995 and he's been helping people learn IT technologies ever since. He has been a sysadmin, instructor, sales engineer, IT manager, and entrepreneur. In his most recent venture, he founded and led a cloud-based training infrastructure company that provided virtual labs for some of the largest software vendors in the world. Guy’s passion is making complex technology easy to understand. His activities outside of work have included riding an elephant and skydiving (although not at the same time).