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diff --git a/doc/src/Eqs/fix_ehex_eom.tex b/doc/src/Eqs/fix_ehex_eom.tex
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+\documentclass[12pt]{article}
+\usepackage{amsmath}
+\begin{document}
+   \begin{align*}
+     \dot{\mathbf r}_i &= \mathbf v_i,  \\
+     \dot{\mathbf v}_i &= \frac{\mathbf f_i}{m_i} + \frac{\mathbf g_i}{m_i}.
+   \end{align*}
+\end{document}
diff --git a/doc/src/Eqs/fix_ehex_f.jpg b/doc/src/Eqs/fix_ehex_f.jpg
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diff --git a/doc/src/Eqs/fix_ehex_f.tex b/doc/src/Eqs/fix_ehex_f.tex
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+\documentclass[12pt]{article}
+\usepackage{amsmath}
+\begin{document}
+ \begin{equation*}
+      \mathbf g_i = 
+      \begin{cases} \frac{m_i}{2}   \frac{ F_{\Gamma_{k(\mathbf r_i)}}}{ K_{\Gamma_{k(\mathbf r_i)}}} 
+               \left(\mathbf v_i -  \mathbf v_{\Gamma_{k(\mathbf r_i)}} \right) &  \mbox{$k(\mathbf r_i)> 0$ (inside a reservoir),} \\
+                  0                                     &  \mbox{otherwise, } 
+      \end{cases}
+  \end{equation*}
+\end{document}
+