How to Initialize Weights in Neural Networks?

Machine learning and deep learning are the most popular terms in the world right now. You can notice how the two technologies have revolutionized the conventional approaches to solve complex problems alongside addressing data-driven decisions. The core element underlying the working mechanisms of machine learning and deep learning are neural networks. Neural networks have been designed along the lines of the architecture of the human brain. 

It is important to understand the significance of biases and weights in neural networks to optimize them for specific uses. Weights are important parameters in machine learning and deep learning models as they help machines in processing information and adapting to different inputs for making predictions. Let us find out more information about the most common methods used for weight initialization in neural networks.

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Importance of Weights in Neural Networks

Neural networks are similar to the human brain in terms of design as they include a complex network of interconnected nodes. The nodes in the network represent neurons in the human brain that work in unison to process information and generate output. Before finding out the best practices to initialize weights in neural network, it is important to learn that connections between all the neurons are not equal. 

Weights help in defining the differences in the connections between different neurons in neural networks. In simple words, weights help in determining the strength of connection between neurons. Weights also determine the effect of output from one neuron on the input for another neuron. Therefore, weights can influence the significance of specific information in the working mechanism of neural networks.

Developers adjust the weights in neural networks iteratively for minimizing the discrepancies between predictions of the networks and actual outputs. You must learn about neural network weight initialization because weights define the capability of neural networks to learn from data. Neural network weights help in capturing the association between input features and desired output. As a result, weights play a major role in helping neural networks with generalization of new data to derive predictions.

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What are the Most Popular Techniques for Initializing Weights in Neural Networks?

You can develop better neural networks for machine learning and deep learning models with ideal weight initialization methods that enable faster training. The best practices to initialize neural network suggest that neural networks would learn different weights in the course of the training process. Interestingly, the initial weights allotted to the network have a major influence on the optimization process. 

Initial weights in neural networks determine the speed and accuracy of convergence of weights. Initial weights are likely to have such a dominant impact due to the complex and high-dimensional loss surface of deep neural networks. Better initialization of weights for neural networks translates into effectiveness of the resultant model. Here are some of the most popular techniques for weight initialization in neural networks.

• Greedy Layer-wise Unsupervised Pre-training

Deep learning researchers had to ponder over queries like ‘how to assign weights in neural network’ for training deep neural networks. One of the earliest solutions to this problem emerged in 2006 with the Greedy Layer-wise Unsupervised Pre-training weight initialization strategy. Let us assume the example of an unsupervised learning model like an autoencoder. 

The autoencoder helps in learning weights between input and the first hidden layer in a neural network. The weights are frozen and serve as essential inputs for learning weights flowing to the next hidden layer. Iterative repetition of the process continues to ensure coverage of all layers in the neural network. The weights that the neural network learns through this approach are subject to fine-tuning for coming up with initial weights.

The effectiveness of this method to initialize weights in neural network depends on its greedy nature. You can notice that the approach does not encourage optimization of initial weights throughout all network layers and focus only on the current layer. 

Subsequently, the neural network learns weights in different layers through an unsupervised approach. The ‘pre-training’ in the algorithm suggests that the initialization process happens before the actual training process. Therefore, new weight initialization techniques emerged over the course of time that did not need any type of pre-training process.

• Zero Initialization Technique

The zero initialization technique emerged as a promising solution for the complexities of early approaches that required pre-training. The name gives out the meaning of zero initialization technique in a subtle way. It involves assigning zero to all weights in neural network and has been considered ineffective for various reasons. 

The most common reason that proves ineffectiveness of zero initialization is its working mechanism in which every neuron would learn the same features in each iteration. You must also remember that the same issue happens for any type of constant initialization. You can use any other constant instead of zero as the initial weights and still end up with the same problem. Here is an example of implementing zero initialization through Keras layers in Python.

# Zero Initialization

from tensorflow.keras import layers

from tensorflow.keras import initializers 

initializer = tf.keras.initializers.Zeros()

layer = tf.keras.layers.Dense(

  3, kernel_initializer=initializer)

• Random Initialization 

The next popular method for weight initialization in neural networks emerged as the answer to setbacks of zero initialization technique. Random initialization helps in overcoming the problems of zero or constant initialization by assigning random values to weights of neuron paths. 

The random technique for neural network weight initialization might seem effective as it does not use zero or a constant value as weights. On the contrary, it can be susceptible to vulnerabilities such as exploding gradient problem, vanishing gradient problem, and overfitting. You can come across two distinct types of random initialization techniques, such as random normal and random uniform techniques.

Random Normal 

Random normal initialization involves initializing weights with values visible in normal distribution. You can implement random normal initialization in Keras layers in Python with the following code.

# Random Normal Distribution

from tensorflow.keras import layers

from tensorflow.keras import initializers

initializer = tf.keras.initializers.RandomNormal(

  mean=0., stddev=1.)

layer = tf.keras.layers.Dense(3, kernel_initializer=initializer)

Random Uniform 

Random uniform initialization works to initialize neural network with weights based on values in uniform distribution. You can implement random uniform initialization technique in Keras layers in Python with the following code.

# Random Uniform Initialization

from tensorflow.keras import layers

from tensorflow.keras import initializers

initializer = tf.keras.initializers.RandomUniform(

  minval=0.,maxval=1.)

layer = tf.keras.layers.Dense(3, kernel_initializer=initializer)

• Xavier or Glorot Initialization

The Xavier or Glorot initialization technique also involves assigning weights to neural networks from values in a uniform distribution. It can help you find how to assign weights in neural network where you have layers that use a sigmoid activation function. You can also call it Xavier Uniform Initialization. Here is an example code to implement Xavier or Glorot initialization in Keras layers of Python.

# Xavier/Glorot Uniform Initialization

from tensorflow.keras import layers

from tensorflow.keras import initializers

initializer = tf.keras.initializers.GlorotUniform()

layer = tf.keras.layers.Dense(3, kernel_initializer=initializer)

• Normalized Xavier or Glorot Initialization

The normalized Xavier or Glorot initialization technique is almost the same as Xavier or Glorot initialization with a glaring difference. You can initialize weights in neural network with this approach by assigning weights from values in a normal distribution. It is also the ideal choice for layers which use a sigmoid activation function. You can implement normalized Xavier or Glorot initialization with the following code in Keras layers of Python.

# Normailzed Xavier/Glorot Uniform Initialization

from tensorflow.keras import layers

from tensorflow.keras import initializers

initializer = tf.keras.initializers.GlorotNormal()

layer = tf.keras.layers.Dense(3, kernel_initializer=initializer)

• HE Uniform Initialization

Another popular initialization technique for neural network weights is HE Uniform Initialization. It is a trusted method to initialize neural network where you will find layers using ReLU as the activation function. The initialization technique involves assigning values from a uniform distribution as the weights. You can implement the HE uniform initialization technique in Keras layers of Python with the following code.

# He Uniform Initialization

from tensorflow.keras import layers

from tensorflow.keras import initializers

initializer = tf.keras.initializers.HeUniform()

layer = tf.keras.layers.Dense(3, kernel_initializer=initializer)

• HE Normal Initialization 

The HE normal initialization technique is also applicable for neural networks that have layers using ReLU activation function. It is different from the HE uniform initialization technique as you would assign weights from values in a normal distribution. The following code example can help you implement HE normal initialization in Keras layers of Python.

# He Normal Initialization

from tensorflow.keras import layers

from tensorflow.keras import initializers

initializer = tf.keras.initializers.HeNormal()

layer = tf.keras.layers.Dense(3, kernel_initializer=initializer)

Final Words

Weight initialization is a crucial requirement in the development of machine learning and deep learning models. Effective neural network weight initialization can help in improving the accuracy of the neural network and the resultant model. Therefore, it is important to choose the right initialization technique according to different factors, such as the activation functions. You can use the zero initialization technique to initialize weights with zero or constant value. However, it can lead to problems of symmetry disruption. 

On the other hand, assigning small random values to neural network weights can create the problem of vanishing gradients. You can use Xavier or Glorot initialization for neural networks that use sigmoid activation functions. Similarly, the HE initialization technique is recommended for neural networks that use ReLU activation function. Dive deeper into the working of neural networks and weight initialization techniques with comprehensive training resources now.