Two-Class Neural Network component

This article describes a component in Azure Machine Learning designer.

Use this component to create a neural network model that can be used to predict a target that has only two values.

Classification using neural networks is a supervised learning method, and therefore requires a tagged dataset, which includes a label column. For example, you could use this neural network model to predict binary outcomes such as whether or not a patient has a certain disease, or whether a machine is likely to fail within a specified window of time.

After you define the model, train it by providing a tagged dataset and the model as an input to Train Model. The trained model can then be used to predict values for new inputs.

More about neural networks

A neural network is a set of interconnected layers. The inputs are the first layer, and are connected to an output layer by an acyclic graph comprised of weighted edges and nodes.

Between the input and output layers you can insert multiple hidden layers. Most predictive tasks can be accomplished easily with only one or a few hidden layers. However, recent research has shown that deep neural networks (DNN) with many layers can be effective in complex tasks such as image or speech recognition. The successive layers are used to model increasing levels of semantic depth.

The relationship between inputs and outputs is learned from training the neural network on the input data. The direction of the graph proceeds from the inputs through the hidden layer and to the output layer. All nodes in a layer are connected by the weighted edges to nodes in the next layer.

To compute the output of the network for a particular input, a value is calculated at each node in the hidden layers and in the output layer. The value is set by calculating the weighted sum of the values of the nodes from the previous layer. An activation function is then applied to that weighted sum.

How to configure

1. Add the Two-Class Neural Network component to your pipeline. You can find this component under Machine Learning, Initialize, in the Classification category.

2. Specify how you want the model to be trained, by setting the Create trainer mode option.

   • Single Parameter: Choose this option if you already know how you want to configure the model.

   • Parameter Range: If you are not sure of the best parameters, you can find the optimal parameters by using the Tune Model Hyperparameters component. You provide some range of values, and the trainer iterates over multiple combinations of the settings to determine the combination of values that produces the best result.

3. For Hidden layer specification, select the type of network architecture to create.

   • Fully connected case: Uses the default neural network architecture, defined for two-class neural networks as follows:

     • Has one hidden layer.

     • The output layer is fully connected to the hidden layer, and the hidden layer is fully connected to the input layer.

     • The number of nodes in the input layer equals the number of features in the training data.

     • The number of nodes in the hidden layer is set by the user. The default value is 100.

     • The number of nodes equals the number of classes. For a two-class neural network, this means that all inputs must map to one of two nodes in the output layer.

4. For Learning rate, define the size of the step taken at each iteration, before correction. A larger value for learning rate can cause the model to converge faster, but it can overshoot local minima.

5. For Number of learning iterations, specify the maximum number of times the algorithm should process the training cases.

6. For The initial learning weights diameter, specify the node weights at the start of the learning process.

7. For The momentum, specify a weight to apply during learning to nodes from previous iterations

8. Select the Shuffle examples option to shuffle cases between iterations. If you deselect this option, cases are processed in exactly the same order each time you run the pipeline.

9. For Random number seed, type a value to use as the seed.

   Specifying a seed value is useful when you want to ensure repeatability across runs of the same pipeline. Otherwise, a system clock value is used as the seed, which can cause slightly different results each time you run the pipeline.

10. Add a labeled dataset to the pipeline, and train the model:

    • If you set Create trainer mode to Single Parameter, connect a tagged dataset and the Train Model component.

    • If you set Create trainer mode to Parameter Range, connect a tagged dataset and train the model by using Tune Model Hyperparameters.

    Note

    If you pass a parameter range to Train Model, it uses only the default value in the single parameter list.

    If you pass a single set of parameter values to the Tune Model Hyperparameters component, when it expects a range of settings for each parameter, it ignores the values, and uses the default values for the learner.

    If you select the Parameter Range option and enter a single value for any parameter, that single value you specified is used throughout the sweep, even if other parameters change across a range of values.

11. Submit the pipeline.

Results

After training is complete:

• To save a snapshot of the trained model, select the Outputs tab in the right panel of the Train model component. Select the Register dataset icon to save the model as a reusable component.

• To use the model for scoring, add the Score Model component to a pipeline.

Next steps

See the set of components available to Azure Machine Learning.