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What is a nullcline? 

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A nullcline is a graphical representation used to understand the behavior of nonlinear systems. It characterizes the points where the rate of change of one variable is zero while the other variable is held constant. Nullclines are commonly used in the study of predator-prey models , neuron models , genetic toggle switches , and FitzHugh-Nagumo oscillators . They provide insights into the steady-state distribution and firing patterns of these systems. In the context of genome analysis, null models are used to identify over- and under-represented sequence motifs. Generating accurate null models for coding sequences is challenging due to the unique constraints imposed by protein coding sequences. However, a method based on the principle of maximum entropy has been developed to generate unbiased random sequences with specified amino acid and GC content .

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A nullcline is a curve in a phase portrait where the derivative of one variable is zero, indicating a steady state or equilibrium point.
A nullcline is a curve in a phase space where the derivative of a variable is zero. It represents the equilibrium points of a dynamical system.
Nullclines are used to characterize and understand the behavior of low-dimensional nonlinear deterministic systems, but they are not a good predictor for discrete state stochastic systems.
Nullclines are curves in a phase plane where the rate of change of one variable is zero, indicating equilibrium points in the system.

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