Fix bug 4774

Author: gajennings

OpenProblemLibrary/Michigan/Chap18Sec3/Q25.pg

@@ -39,7 +39,7 @@ loadMacros(
   "PGstandard.pl",
   "PGchoicemacros.pl",
   "MathObjects.pl",
-  "parserFormulaUpToConstant.pl",
+  "parserMultiAnswer.pl",
   "PGcourse.pl"
 );
 
@@ -113,6 +113,33 @@ if ( $which ) {
     $chg2d = "-$a";
 }
 
+$part_b = MultiAnswer($f,$f0,$f1,$chg2)->with(
+  singleResult => 0,
+  checker => sub{ 
+    my ( $correct, $student, $self ) = @_;
+    my ( $f_stu, $f0_stu, $f1_stu, $chg2_stu ) = @{$student};
+    my @score = (0,0,0,0);
+    if ( ($fx == $f_stu->D('x')) and ($fy == $f_stu->D('y')) ){
+      $score[0]=1;
+    }
+    else{ 
+      $self -> setMessage(1,"The gradient of your function must equal \(\nabla f\)"); 
+      return @score;
+    }
+    if ( $f0_stu == $f_stu->eval(x=>0,y=>0) ){
+      $score[1]=1;
+    }
+    if ( $f1_stu == $f_stu->eval(x=>1,y=>pi/2) ){
+      $score[2]=1;
+    }
+    if ( $score[1] == 1 and $score[2] == 1 and 
+         $chg2_stu == ($f1_stu - $f0_stu) ){
+       $score[3]=1;
+    }
+    return @score; 
+  }
+);
+
 
 Context()->texStrings;
 TEXT(beginproblem());
@@ -159,28 +186,30 @@ $PAR
 ${BBOLD}(b)$EBOLD
 By computing values of \( f \).  To do this,
 $BR
-First find \( f(x,y) = \) \{ ans_rule(45) \}
+First find \( f(x,y) = \) \{ $part_b->ans_rule(45) \}
 $BR
 Thus
 $BR
-\( f(0,0) = \) \{ ans_rule(25) \} and
-\( f(1,\pi/2) = \) \{ ans_rule(25) \},
+\( f(0,0) = \) \{ $part_b->ans_rule(25) \} and
+\( f(1,\pi/2) = \) \{ $part_b->ans_rule(25) \},
 $BR
-and the change in \(f\) is \{ ans_rule(35) \}.
+and the change in \(f\) is \{ $part_b->ans_rule(35) \}.
 
 END_TEXT
 Context()->normalStrings;
 
+#part a answers
+
 ANS($rx->cmp() );
 ANS($ry->cmp() );
 ANS($integr->cmp() );
 ANS($int1->cmp() );
 ANS($int2->cmp() );
 ANS($chg1->cmp() );
-ANS($f->cmp(upToConstant=>1) );
-ANS($f0->cmp() );
-ANS($f1->cmp() );
-ANS($chg2->cmp() );
+
+#part b answers
+
+ANS($part_b->cmp()); 
 
 Context()->texStrings;
 SOLUTION(EV3(<<'END_SOLUTION'));