[WWcvs] pg: Fixed check to use a variable that is known to be in the context (rather than incorrectly assuming 'x' is there).

[dpvc v. a. <we...@ma...>]

Log Message:
-----------
Fixed check to use a variable that is known to be in the context
(rather than incorrectly assuming 'x' is there).

Modified Files:
--------------
    pg/macros:
        parserFormulaUpToConstant.pl

Revision Data
-------------
Index: parserFormulaUpToConstant.pl
===================================================================
RCS file: /webwork/cvs/system/pg/macros/parserFormulaUpToConstant.pl,v
retrieving revision 1.6
retrieving revision 1.7
diff -Lmacros/parserFormulaUpToConstant.pl -Lmacros/parserFormulaUpToConstant.pl -u -r1.6 -r1.7
--- macros/parserFormulaUpToConstant.pl
+++ macros/parserFormulaUpToConstant.pl
@@ -192,9 +192,12 @@
   my $result = $ans->{correct_value} <=> $student;  # compare encodes the reason in the result
   $self->cmp_Error($ans,"Note: there is always more than one posibility") if $result == 2 || $result == 3;
   if ($result == 3) {
-    $self->context->flags->set(no_parameters=>0);
-    $result = 1 if $self->removeConstant+"n01+n00x" == $student+"x"; # must use both parameters
-    $self->context->flags->set(no_parameters=>1);
+    my $context = $self->context;
+    $context->flags->set(no_parameters=>0);
+    $context->variables->add(x00=>'Real');
+    $result = 1 if $self->removeConstant+"n01+n00x00" == $student+"x00"; # must use both parameters
+    $context->variables->remove('x00');
+    $context->flags->set(no_parameters=>1);
   }
   $self->cmp_Error($ans,"Your answer is not the most general solution") if $result == 1;
   $self->cmp_Error($ans,"Your formula should be linear in the constant '$student->{constant}'")