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R Data Mining by Andrea Cirillo

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The math behind logistic regression

We just said that our logistic function is able to always return a number enclosed within zero and one, but how does this function obtain that desirable result? First of all, let's start with the logistic function formula:

As you can see, we have a ratio between a strange term ex and one plus the same strange term ex. What is that strange term? It turns out that it is the natural number e, which is approximately equal to 2.7183, raised to the power of x. The ex term is therefore named the exponential function, since it's the function obtained raising to an exponent equal to x. What is the shape of this ...

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