Log-normal Distribution. The lognormal distribution (the term first used by Gaddum, 1945) has the probability density function:

f(x) = 1/[x(2)1/2] * exp(-[log(x)-µ]2/22)
0 x <
µ > 0
> 0

µ     is the scale parameter
   is the shape parameter
e     is the base of the natural logarithm, sometimes called Euler's e (2.71...)

The animation above shows the Log-normal distribution with mu equal to 0 for sigma equals .10, .30, .50, .70, and .90.

Logarithmic Function. This fits to the data, a logarithmic function of the form:

y = q*[logn(x)] + b
statická ukážka