Machine Learning

The Sigmoid and its Derivative

The sigmoid function, \(\sigma(x)\), is also called the logistic function, or expit [1]. It is the inverse of the logit function. Its function definition is: \[ \sigma(x) = \frac{1}{1+e^{-x}} \tag{1}\] Let’s get familiar by plotting this function first: And just to be complete, here is the python code that produced the above plot: We see

Machine Learning

What is a Logit?

The term logit has different meanings in math and in the TensorFlow library. In TensorFlow it means “Per-label activations, typically a linear output. These activation energies are interpreted as unnormalized log probabilities.” What this means is: the logits are the vector you get as output of the last layer of your neural network. It is

Math, Probability and Statistics

Variance, Covariance, Autocovariance…what?

This article aims to distinguish between Variance, Covariance, Correlation, Autocovariance, and Autocorrelation. Furthermore there will be a numerical discrete example for computing the Autocorrelation in python. This article will not derive the formulae mathematically, only state them. Variance measures the spread of a r.v. (random variable). \[\begin{equation} Var(X) = E[( X-\bar{x} )^2] = \sum_{i=1}^{n} {

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