Natural logarithm
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The natural logarithm ln(x) is the logarithm to the base ‘e’, and mathematically the inverse function of the exponential function ex.
So for example ln(100) = 4.60517...
And e4.60517... = 100
Also known for short as the 'natural log'.
Also sometimes known - loosely - as the 'Napierian logarithm'.
(Not to be confused with Lognormal, which is different.)