Experimental X-ray diffraction profiles and calculated curves for different choices of the basic units in the Markov chain: (a) A–B, (b) A–AB, (c) B–AB model. Arrows in (c) show the peak positions for the ordered ABAB phase. The probabilities p, q and corresponding value m are indicated at each curve. The basic units used for the calculation are schematically shown in the insets. The diffraction peak positions for the pure A and B phases are marked by orange dotted lines and blue dashed lines, respectively.