  It has been proven that the accessibility of the target sites has a critical
influence for miRNA and siRNA. In this paper, we present a program, rip2.0, not
only the energetically most favorable targets site based on the
hybrid-probability, but also a statistical sampling structure to illustrate the
statistical characterization and representation of the Boltzmann ensemble of
RNA-RNA interaction structures. The outputs are retrieved via backtracing an
improved dynamic programming solution for the partition function based on the
approach of Huang et al. (Bioinformatics). The $O(N^6)$ time and $O(N^4)$ space
algorithm is implemented in C (available from
\url{http://www.combinatorics.cn/cbpc/rip2.html})
