Probability density function is a statistical expression defining the likelihood of a series of outcomes for a continuous variable, such as a stock or ETF return.

A class of probability density estimates can be obtained by penalizing the likelihood by a functional which depends on the roughness of the logarithm of the density. The limiting case of the estimates ...

Leonard Fortuin, Five Popular Probability Density Functions: A Comparison in the Field of Stock-Control Models, The Journal of the Operational Research Society, Vol. 31, No. 10 (Oct., 1980), pp.