The IBDSh can be uesd to do the following things: 1.calculate the distribution of the time of the most recent common ancestor(tMRCA); 2.calculate the distribution of the IBD sharing in the same or across the population; 3.Estimate the population size and migration rate in MIBD method. We performe a grid search to find the least square solution,the detailed descriptions are in Least_Square_fun.m and Grid_Search.m. Note: ms-IBD can be found at https://github.com/xyang619/ms-IBD