Probability, Random Variables, and Random Processes: Theory and Signal Processing Applications
by John J. Shynk
9.18 EXPECTATION–MAXIMIZATION ALGORITHM
The expectation–maximization (EM) algorithm is a recursive technique for finding the ML estimate in situations where there are unobservable factors influencing the samples. In conventional ML estimation, the likelihood function
or, equivalently, the log-likelhood function
is used to estimate θ from
. Suppose the samples are incomplete in the sense that there are other random variables correlated with {Xn}, but these are not directly measurable. Let those random variables be denoted by
.
Consider the joint pdf
for measurable X and unmeasurable Y. If Y is also measurable, then the ML estimator for θ would be the function of X and Y that maximizes the joint pdf. However, since only X is observable, it is possible to estimate θ by maximizing only
, which can be expressed as
(9.273)
The influence of the nonmeasurable Y on the estimate is ignored in conventional ...
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Read now
Unlock full access