Add the definition of e in ipm.tex

tex/sections/ipm.tex

@@ -109,8 +109,8 @@ \subsection{Solving the KKT conditions with the interior-point method}
   \end{bmatrix} = 0
    \; .
 \end{equation}
-We introduce in \eqref{eq:kkt_ipm} the diagonal matrices $X = \diag(x_1, \cdots, x_n)$
-and $S = \diag(s_1, \cdots, s_{m_i})$.
+We introduce the diagonal matrices $X = \text{diag}(x_1, \cdots, x_n)$ and
+$S = \text{diag}(s_1, \cdots, s_{m_i})$, along with the vector of ones $e$.
 As we drive the barrier parameter $\mu$ to $0$, the solution of the
 system $F_\mu(x, s, y, z, u, v) = 0$ tends to the solution of the
 KKT conditions~\eqref{eq:kktconditions}.