objects simulation using matlab (plot function)

hi all, i really need your help i try to implement a SEM algorithm(Stochastic Expectation Maximisation)in order to extract a set of objects,but i have a problem in the S step which consist to simulate a set of geometric objects following a probability law( for example a set of circles with different values of radius). note:an object is defined by coordinates x and y with a mark in our case r:radius please if someone have an idea don't hesitate to tell me