Robustness analysis.

<p>Each negative feedback network motif is assessed for its robustness by computing the value of the robustness measure <i>R</i> (Equation(5)) upon stimulation with TGF-β alone or together with BMP. To represent the model output, we use the (<b>A</b>) peak species concentration (<i>m_p</i> metric; Equation(1)), (<b>B</b>) time of the peak species concentration (<i>m_t</i> metric; Equation(2)), and (<b>C</b>) signal duration (<i>m_d</i> metric; Equation(3)) as metrics of the <i>pS1S4_n</i> and <i>pS2S4_n</i> signal response.