Add example for shiftSample. (modelica#3233)

* Add example for shiftSample.
Closes modelica#3040
Co-authored-by: Henrik Tidefelt <henrikt@wolfram.com>

chapters/synchronous.tex

@@ -735,6 +735,22 @@ \subsection{Sub-Clock Conversion Operators}\label{sub-clock-conversion-operators
 Clock y1 = shiftSample(u, 2);       // ticks: 2.0, 3.0, $\ldots$
 Clock y2 = shiftSample(u, 2, 3);    // error (resolution must be 1)
 \end{lstlisting}
+Additional example showing the full form:
+\begin{lstlisting}[language=modelica]
+  Integer intervalCnt(start=2);
+  Integer cnt(start=0);
+  Clock u = Clock(intervalCnt,1);
+  Clock s1 = shiftSample(u, 3, 2);
+equation
+   when u then
+     cnt = previous(cnt) + 1;
+     intervalCnt = if (cnt>=2) then 1 else previous(intervalCnt);
+   end when;
+\end{lstlisting}
+Here \lstinline!u! ticks at 0, 2, 3, 4, 5, 6.
+First you \lstinline!superSample! to split each sampling interval in two equal parts leading to the ticks 0.0, 1.0, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0.
+Then the simple \lstinline!shiftSample! removes the first three ticks giving 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0.
+And finally every other point is removed by \lstinline!subSample!, and \lstinline!s1! ticks at 2.5, 3.5, 4.5, 5.5.
 \end{nonnormative}
 \end{semantics}
 \end{operatordefinition}