Added a tex file for the equations of pair rounded/polygon and rounded/polyhedron

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\begin{eqnarray*}

 F_n &=& k_n \delta_n - c_n v_n, \qquad \delta_n \le 0 \\

     &=& -k_{na} \delta_n - c_n v_n, \qquad 0 < \delta_n \le r_c \\

     &=& 0 \qquad \qquad \qquad \qquad \delta_n > r_c \\

 F_t &=& \mu k_n \delta_n - c_t v_t, \qquad \delta_n \le 0 \\

     &=& 0 \qquad \qquad \qquad \qquad \delta_n > 0

\end{eqnarray*}

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