This function calculates the ratio of exponential network information sharing prior probabilities.
Network information collected using the function
Returns the ratio [prior of new network]/[prior of old network].
For information about the exponential information sharing prior, see:
Husmeier et al. (2010), "Inter-time segment information sharing for non-homogeneous dynamic Bayesian networks", NIPS.
Dondelinger et al. (2012), "Non-homogeneous dynamic Bayesian networks with Bayesian regularization for inferring gene regulatory networks with gradually time-varying structure", Machine Learning.