Backpropagation, short for “backward propagation of errors,” is an algorithm commonly used to train artificial neural networks by iteratively adjusting the network’s weights to minimize the difference between predicted and target outputs.
The backpropagation algorithm calculates the gradients of the network’s error with respect to each weight in the network. It does this by propagating the error information backward through the network, starting from the output layer and moving toward the input layer. This process allows the algorithm to determine how much each weight contributes to the overall error.
What are the key steps involved in the backpropagation algorithm?
- Forward pass: During the forward pass, input data is fed into the neural network, and activations are computed layer by layer until the output is generated. Each neuron’s activation is obtained by applying an activation function to the weighted sum of its inputs.
- Error computation: The error between the predicted output and the desired target output is calculated using a chosen error function, such as mean squared error or cross-entropy. This error is used as a measure of how well the network is performing.
- Backward pass: In the backward pass, the gradients of the error with respect to the weights of the network are computed. This is done by iteratively applying the chain rule of calculus to propagate the error information backward through the layers. The gradients represent the contribution of each weight to the overall error.
- Weight update: Once the gradients are computed, the network’s weights are adjusted to minimize the error. This is typically done using an optimization algorithm, such as gradient descent or its variants. The weights are updated in the opposite direction of the gradients, scaled by a learning rate that determines the size of the weight updates.
- Iteration: Steps 1-4 are repeated for multiple iterations or epochs, with the network being presented with different training examples in each iteration. This iterative process allows the network to gradually adjust its weights and improve its performance over time.
By iteratively updating the weights based on the computed gradients, the backpropagation algorithm enables the neural network to learn from the training data and adjust its parameters to better approximate the desired output. This process continues until the network’s performance reaches a satisfactory level or converges to a local minimum in the optimization process.