Softmax Function: An Introduction
The softmax function plays a crucial role in processing K values, converting them into real numbers that sum up to 1. It processes all kinds of numerical inputs, be they negative, zero, positive, or greater than one, and normalizes them to lie between 0 and 1. These outputs are then interpreted as probabilities.
Behavior of Softmax Function
In instances where the input is minimal or negative, the softmax function translates it into a low probability score. Conversely, a large input value becomes a high probability, but it always remains between 0 and 1. This function, sometimes called Softargmax or multi-class logistic regression, is recognized for its role as a multi-class classification extension of logistic regression. Owing to its similarity with the sigmoid function in logistic regression, it has acquired these alternative names. Particularly, it's invaluable when classifying in environments where classes don’t overlap.
Softmax in Neural Networks
Many multilayer neural networks feature a penultimate layer producing real-value scores. These scores can be difficult to normalize. Enter softmax, which turns these scores into a probability distribution suitable for user presentation or as input for other systems. This transformation establishes softmax as an ideal concluding layer in a neural network.
Consider a convolutional neural network determining whether an image portrays a human or a dog, assuming these categories are mutually exclusive. The network's final layer emits unnormalized data, which doesn't readily convert into probabilities. Integrating a softmax layer refines these numbers into a probability distribution. Thus, the output probability can be shared with users or directed into other machine learning systems without requiring prior normalization.
When discerning between humans and dogs with only two categories, the network must choose one, even if the image represents neither. To address this, modifying the neural network to feature a third generic output is beneficial.
Training Neural Networks with Softmax
In training a neural network to differentiate between images of dogs (class 1) and humans (class 2), the optimal result for a dog image would be vector [1, 0] and [0, 1] for a human image. The final layer, however, yields non-probabilistic scores. Integrating a softmax layer close to the end refines this output into a probability distribution.
Training starts with random weights, and a loss function measures the deviation between network output and desired results. A smaller loss function indicates alignment with the correct class. Because softmax is continuously differentiable, it permits weight adjustments to minimize the loss function, enhancing performance.