An example apparatus includes a crossbar array of signal lines and control lines. The example apparatus also includes an input controller in circuit with the control lines. The input control is to select one of the control lines. The example apparatus also includes first resistive elements connected between corresponding ones of the control lines and corresponding ones of the signal lines. The first resistive elements have first conductances set to operate as a matrix of probabilities that define a fixed transition kernel of a Markov Chain. The example apparatus also includes second resistive elements in circuit with the signal lines. The second resistive elements have second conductances set to select one of the signal lines exclusive of others of the signal lines based on a subset of the probabilities in the matrix of the probabilities.