 Two model simplification methods are applied to multi-variable models: (1) the phase response curves (PRC) and the circadian phase dynamics of these models are generated by impulse response simulation;
<meaning-changed>  Two model simplification methods are applied to multi-variable models: (1) the phase response curves (PRC) and the circadian phase dynamics of these models are generated by impulse response simulation;
 Two model simplification methods are applied to these high-order models: the phase response curves (PRC) and the circadian phase dynamics of these models are generated by impulse response simulation;