DataPredict

Using Neural Networks, Part 1

Neural networks are classification and regression model where it can predict a number of classes (classification) or range of values (regression).

Neural networks typically contains a number of layers. Inside each of those layers, they contain a number of neurons that determines the output of the model.

Getting Started

Before we start building layers for our neural network, we first need to define a number of stuff in our neural network code.

local NeuralNetworkModel = DataPredict.Models.NeuralNetwork.new() -- Creating a new model object.

NeuralNetworkModel:setClassesList({0, 1}) -- Setting exising classes, but these can be automatically set by our model if the model uses batch gradient descent.

And under here, we have our data. Notice that all of our first column of the feature matrix contain values of 1. Those are bias values.

local featureMatrix = {

	{1, 0,  0},
	{1, 10, 2},
	{1, -3, -2},
	{1, -12, -22},
	{1,  2,  2},
	{1, 1,  1},
	{1, -11, -12},
	{1,  3,  3},
	{1, -2, -2},

}

local labelVector = {

	{1},
	{1},
	{0},
	{0},
	{1},
	{1},
	{0},
	{1},
	{0}

}

As you can see the feature matrix contains 3 columns, which means that we need 3 input neurons. It also contains the bias values, so one of the three input neurons must be a bias neuron.

Creating Layers

We have two ways of creating our neural network layers:

  1. Create all layers in one go.

  2. Create each layer with their own individual settings.

Below, I will show the codes that demonstrates these two options.

Creating All Layers

We will use createLayers() function to create the layers. The first parameters takes in a table of integers, where the index determines the position and the values determines the number of neurons.

local numberOfNeuronsWithoutBiasArray = {2, 3, 2}

NeuralNetworkModel:createLayers(numberOfNeuronsArray)

Using this function, we have set 2 neurons at first layer, 3 neurons at second layer and 2 neurons at final layer.

Do make note that the bias neurons are not added yet to each of the layer (except the final layer) and will be added automatically once this function is called.

In other words, after running the function, the model will have 3 neurons at first layer, 4 neurons at second layer and 2 neurons at final layer.

Creating Individual Layers

If you wish to have more control over each layer, then we can use addLayer() function. Below, we will show on how to create a single layer.

NeuralNetworkModel:addLayer(2, true, "Tanh", 0.001)

The first parameter determines the number of neurons on that layer, the second parameter is to set whether or not to add a bias neuron. The third parameter is to set the activation function for that layer. The fourth parameter determines the learning rate for that layer.

Do make note that if you add a bias neuron, it will not be included in the first parameter. (e.g. Before adding a bias neuron, it is 2 neuron, but after adding a bias neuron, it becomes three.)

Once that is covered, we will now show you on how to add multiple layers using the same function.


local learningRate1 = 0.0001

local learningRate2 = 0.01

NeuralNetworkModel:addLayer(2, true)

NeuralNetworkModel:addLayer(3, true, "Tanh", learningRate1)

NeuralNetworkModel:addLayer(2, false, "StableSoftmax", learningRate2)

In this code, we have set 3 neurons (including the bias neuron) at first layer, 4 neurons (including the bias neuron) at second layer and 2 neurons (without the bias neuron) at final layer.

Optimizers

If you wish to use optimizers on multiple layers, then you need one optimizer for each layer. The example is shown below.


local AdaptiveGradientOptimizer = DataPredict.Optimizers.AdaptiveGradient

local Adagrad1 = AdaptiveGradientOptimizer.new()

local Adagrad2 = AdaptiveGradientOptimizer.new()

NeuralNetworkModel:addLayer(2, true) -- For the first layer, we can only choose number of neurons and set whether or not it has bias.

NeuralNetworkModel:addLayer(3, true, "Tanh", nil, Adagrad1)

NeuralNetworkModel:addLayer(2, false, "StableSoftmax", nil, Adagrad2)

Regularization

For regularization, you can use one regularization object for each layer. You can also use one regularization object for all layers. The examples are shown below.


local Regularization = DataPredict.Others.Regularization

local Reg1 = Regularization.new()

local Reg2 = Regularization.new()

-- Different regularization objects for each layers.

NeuralNetworkModel:addLayer(2, true)

NeuralNetworkModel:addLayer(3, true, "Tanh", nil, nil, Reg1)

NeuralNetworkModel:addLayer(2, false, "StableSoftmax", Reg2)

-- Same regularization object for each layers.

NeuralNetworkModel:addLayer(2, true, "Tanh", nil, nil, Reg1)

NeuralNetworkModel:addLayer(3, true, "Tanh", nil, nil, Reg1)

NeuralNetworkModel:addLayer(2, false, "StableSoftmax")

Wrapping it all up

The tutorial covers the basics on how to create your own neural networks.

Further information relating to neural networks can be found in the API reference here.

That’s all for today!