--- loncom/homework/templates/Plot_data.problem	2007/10/29 16:21:07	1.4
+++ loncom/homework/templates/Plot_data.problem	2010/08/01 14:15:12	1.6
@@ -1,12 +1,19 @@
 <problem>
 
 <script type="loncapa/perl">
+#
+# This example populates arrays with the x and y coordinates of the plot.
+# For continuous functions, another approach is to use curve plots.
+#
 $amplitude = &random(1,4,0.5);
 $x_min = -5;
 $x_max =  5;
 for ($x=$x_min;$x<=$x_max;$x=$x+0.05) {
    push(@X,$x);
    push(@Y,$amplitude*sin($x));
+# Safeguard:
+# The following line limits the size of the array to 1000 to avoid infinite loops
+   if (($#X>1000) || ($#Y>1000)) { last; }
 }
 </script>
 
@@ -20,13 +27,13 @@ for ($x=$x_min;$x<=$x_max;$x=$x+0.05) {
     </curve>
 </gnuplot>
 
-<startouttext />What is the amplitude of this function?<endouttext />
+<startouttext />
+What is the amplitude of this function?
+<endouttext />
 
 <numericalresponse answer="$amplitude" format="2s">
     <responseparam name="tol" type="tolerance" description="Numerical Tolerance" default="5%" />
-    
     <textline readonly="no" />
-
 </numericalresponse>
-</problem>
 
+</problem>