# Difference of the summations in the formula included in the cross entropy method

1. Oct 17, 2011

### TheMarksman

Hi all,

I am confused with this formula from the cross entropy method

http://img406.imageshack.us/img406/3648/unlednz.png [Broken]

How would the summation on top with {r,s} (these are nodes: "r" represents the current node and "s" represents the next node) differ from the summation below with just {r} when the all the other terms are the same (∏ represents the entire path)? Pt,rs is the probability for the neighboring nodes of "r".

Does this mean that the nodes r,s on top of the equation are only included in the summation when the both r,s are in the path while the node r in the equation beloe only requires r to be in the path to be included in the summation?

The question is just about the summation up to ∏j on top and below so the terms that follow (cartesian products) are irrelevant. Thanks for reading my question.

Last edited by a moderator: May 5, 2017