BigSnarf blog

Infosec FTW

What is applied machine learning?

“Look, a machine learning algorithm really is a lookup table, right? Where the key is the input, like an image, and the value is the label for the input, like ‘a horse.’ I have a bunch of examples of something. Pictures of horses. I give the algorithm as many as I can. ‘This is a horse. This is a horse. This isn’t a horse. This is a horse.’ And the algorithm keeps those in a table. Then, if a new example comes along — or if I tell it to watch for new examples — well, the algorithm just goes and looks at all those examples we fed it. Which rows in the table look similar? And how similar? It’s trying to decide, ‘Is this new thing a horse? I think so.’ If it’s right, the image gets put in the ‘This is a horse’ group, and if it’s wrong, it gets put in the ‘This isn’t a horse’ group. Next time, it has more data to look up.

One challenge is how do we decide how similar a new picture is to the ones stored in the table. One aspect of machine learning is to learn similarity functions. Another challenge is, What happens when your table grows really large? For every new image, you would need to make a zillion comparisons…. So another aspect of machine learning is to approximate a large stored table with a function instead of going through every image. The function knows how to roughly estimate what the corresponding value should be. That’s the essence of machine learning — to approximate a gigantic table with a function. This is what learning is about.”

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