The logarithm in base e; either the function that given x\! returns y\! such that e^y = x\! or the value of y\!
The natural logarithm can be used to integrate 1/x.
A logarithm in which the base is the irrational number e (= 2.71828...). For example, ln 10 = log10 = approximately 2.30258. Also called Napierian logarithm