An illustrative example is a bistable system that can be characterized by a hidden Markov model (HMM) subject to measurement noise. Such models are employed for many biological systems: They have, for example, been used in development, cell signaling, activation/deactivation, logical processing and non-equilibrium thermodynamics. For instance, the behavior of the Sonic hedgehog (Shh) transcription factor in "Drosophila melanogaster" can be modeled with an HMM. The (biological) dynamical model consists of two states: A and B. If the probability of a transition from one state to the other is defined as formula_1 in both directions, then the probability to remain in the same state at each time step is formula_45. The probability to measure the state correctly is formula_46 (and conversely, the probability of an incorrect measurement is formula_47).