Note about special case, and use proper syntax for example.

chapters/arrays.tex

@@ -1447,14 +1447,16 @@ \section{Empty Arrays}\label{empty-arrays}
 \begin{lstlisting}[language=modelica]
 Real[0, m] * Real[m, n] = Real[0, n] // empty matrix
 Real[m, n] * Real[n, 0] = Real[m, 0] // empty matrix
-Real[m, 0] * Real[0, n] = fill(0.0, m, n) // non-empty matrix of zeros
+Real[m, 0] * Real[0, n] = fill(0.0, m, n) // matrix of zeros
+// Note fill(0.0, m, n) will be an empty matrix if m or n is 0
 \end{lstlisting}
 
 \begin{example}
 \begin{lstlisting}[language=modelica]
-Real u[p], x[n], y[q], A[n, n], B[n, p], C[q, n], D[q, p];
-der(x) = A * x + B * u
-y = C * x + D * u
+  Real u[p], x[n], y[q], A[n, n], B[n, p], C[q, n], D[q, p];
+equation
+  der(x) = A * x + B * u
+  y = C * x + D * u
 \end{lstlisting}
 Assume $\text{\lstinline!n!} = 0$, $\text{\lstinline!p!} > 0$, $\text{\lstinline!q!} > 0$: Results in \lstinline!y = D * u!.
 \end{example}