Probability Mass Functions for which Sources have the Maximum Minimum Expected Length
Let P_n be the set of all probability mass functions (PMFs) (p_1,p_2,...,p_n) that satisfy p_i>0 for 1≤ i ≤ n. Define the minimum expected length function L_D :P_n →R such that L_D (P) is the minimum expected length of a prefix code, formed out of an alphabet of size D, for the discrete memoryless source having P as its source distribution. It is well-known that the function L_D attains its maximum value at the uniform distribution. Further, when n is of the form D^m, with m being a positive integer, PMFs other than the uniform distribution at which L_D attains its maximum value are known. However, a complete characterization of all such PMFs at which the minimum expected length function attains its maximum value has not been done so far. This is done in this paper.
READ FULL TEXT