Approximate entropy

Approximate Entropy (ApEn) is a way of measuring how much a set of data differs from one set of data to another. It looks for patterns in the data and measures how similar one set of data is to the others. For example, if we have a set of numbers and there is only one pattern that keeps appearing over and over, then the ApEn will be low. But if there are many patterns and variations, then the ApEn will be high.