Logistic Regression

The logistic, or logit, model is a linear model that has been effectively used for classification tasks in a number of different domains. Recalling the definition of the OLS model from the previous section, the logistic regression model takes as input a linear combination of the input features. In this section, we will use it to classify images of handwritten digits. In understanding the logistic model, we also take an important step in understanding the operation of a particularly powerful machine learning model – artificial neural networks. So, what exactly is the logistic model? Like the OLS model, which is composed of a linear or straight-line function, the logistic model is composed of the standard logistic function, which, in mathematical terms, looks something like this:

Figure 5.7: Logistic function

In practical terms, when trained, this function returns the probability of the input information belonging to a particular class...