Programming Machine Learning

Going Multiclass

Let’s recap where we are and where we want to go. We have a binary classifier that’s hardwired to recognize a specific digit, such as 5. It passes images through a weighted sum, and then a sigmoid. The result is a number ranging from 0 to 1. Then we round that number to either 1 or 0, because we want a binary result—a straight “yes, this is a 5” or “no, this isn’t a 5,” as illustrated in the following picture:

And here is where we want to go: we want a program that takes an image and tells us which digit that image represents, from 0 to 9:

Let’s see how we can go from here to there. First, focus on that box right at the center ...