--- loncom/homework/templates/functionplottwo.problem	2010/11/12 02:16:24	1.1
+++ loncom/homework/templates/functionplottwo.problem	2015/12/23 19:36:24	1.5
@@ -3,16 +3,32 @@
 <startouttext />
 Make a sketch of the electrostatic potential (zero at infinity) of a negative point charge located at x=$x m.
 <endouttext />
-<functionplotresponse xaxisvisible="yes" xlabel="x [m]" gridvisible="yes" ylabel="V(x) [V]" id="11" xmax="30" yaxisvisible="yes" xmin="-4" ymin="-10" ymax="10">
+<functionplotresponse xaxisvisible="yes" xlabel="x [m]" gridvisible="yes" ylabel="V(x) [V]" id="11" xmax="30" yaxisvisible="yes" xmin="-4" ymin="-10" ymax="10" answerdisplay="-4/abs(x-$x)">
+<functionplotelements>
 <spline initx="-2" inity="0" index="A" order="2" scalex="4" />
 <spline index="B" order="2" initx="12" inity="0" scalex="4" />
-<functionplotrule relationship="eq" value="undef" derivative="0" xinitial="$x" />
-<functionplotrule relationship="lt" value="0" derivativeorder="0" xinitiallabel="start" xfinallabel="chargeleft" />
+</functionplotelements>
+<functionplotruleset>
+<functionplotrule relationship="eq" value="undef" xinitial="$x" index="chargeposition" derivativeorder="0" />
+<functionplotrule relationship="lt" value="0" derivativeorder="0" xinitiallabel="start" xfinallabel="chargeleft" index="negleft" />
 <functionplotrule relationship="lt" value="0" derivativeorder="1" xinitiallabel="start" xfinallabel="chargeleft" />
-<functionplotrule relationship="le" value="0" derivativeorder="2" xinitiallabel="start" xfinallabel="chargeleft" />
+<functionplotrule relationship="le" value="0" derivativeorder="2" xinitiallabel="start" xfinallabel="chargeleft" percenterror="20" />
 <functionplotrule relationship="eq" xinitiallabel="chargeleft" xfinallabel="chargeright" value="undef" derivativeorder="0" />
-<functionplotrule relationship="lt" value="0" derivativeorder="0" xinitiallabel="chargeright" xfinallabel="end" />
+<functionplotrule relationship="lt" value="0" derivativeorder="0" xinitiallabel="chargeright" xfinallabel="end" index="negright" />
 <functionplotrule relationship="gt" value="0" derivativeorder="1" xinitiallabel="chargeright" xfinallabel="end" />
-<functionplotrule relationship="le" value="0" derivativeorder="2" xinitiallabel="chargeright" xfinallabel="end" />
+<functionplotrule relationship="le" value="0" derivativeorder="2" xinitiallabel="chargeright" xfinallabel="end" percenterror="20" />
+</functionplotruleset>
+
+<hintgroup showoncorrect="no">
+<hintpart on="chargeposition">
+<startouttext />The charge is not in the correct position.<endouttext />
+</hintpart>
+<hintpart on="negleft">
+<startouttext />The potential is zero at negative infinity, and the charge is negative.<endouttext />
+</hintpart>
+<hintpart on="negright">
+<startouttext />The potential is zero at positive infinity, and the charge is negative.<endouttext />
+</hintpart>
+</hintgroup>
 </functionplotresponse>
 </problem>