** Using WeBWorK **

• if the student enters the right answer, all is well
• if a student enters a function, the problem gives a message saying in essence that a number is expected but it was given a formula instead

I want to suppress this last message. I am not sure how to do that. For convenience, I will paste the problem below.

John

DOCUMENT() ; # This should be the first executable line in the problem.

loadMacros(
"PG.pl",
"PGbasicmacros.pl",
"PGchoicemacros.pl",
"PGanswermacros.pl",
"PGauxiliaryFunctions.pl",
"MathObjects.pl",
"parserMultiAnswer.pl",
"PGasu.pl"
);

TEXT(beginproblem()) ;
$showPartialCorrectAnswers = 0;
install_problem_grader(~~&std_problem_grader);

Context('Numeric');

$a= non_zero_random(-4,4);
$b= non_zero_random(-4,4);
$z = random (1,3);
$k = non_zero_random(-4,4);
if ($k==$b){$c = $b}
elsif ($z==3) {$c = $b-$k}
else {$c = $b}


$d = non_zero_random(-4,4); # this is exact if $b==$c
$n = random(1,4);
$n1=$n+1;
$m = random(2,4);
$m1= $m+1;


Context()->strings->add("not exact" =>{"not exact"});
Context()->variables->add(A=>'Parameter');
Context()->variables->add(K=>'Parameter');
Context()->variables->add('y'=>'Real');

if ($c != $b) {$Fxy = String("not exact");}
else {
$Fxy = Compute("A*(($a/$m1) x^{$m1}+${b}x y + (${d}/$n1)y^${n1})+K");
}



$num = nicestring([-$a, -$b], ["x^{$m}", 'y']);
$ypow = "y^{$n}";
$ypow = "y" if ($n==1);
$den = nicestring([$c, $d], ['x', $ypow]);


$mp = MultiAnswer("$a x^$m + $b y","$c x + $d y^$n", $Fxy)->with(
checker => sub {
my $correct = shift; my $student = shift; my $self = shift;
my ($F,$G,$cFxy) = @{$correct};
my ($f,$g, $fxy) = @{$student};
#$mp->setMessage(1,"The function can't be the identity");
return [0,0,0] unless $F/$G == $f/$g;
# Since M and N can be multiplied by a common function, no further check
# Now check the last part
if ($c==$b) {
if (Formula($fxy)->isConstant) {
$mp->setMessage(3,"The function cannot be constant");
return [1,1,0];
}
}
return [1,1,1] if $cFxy == $fxy;
return [1,1,0];
}
);

BEGIN_TEXT
Use the "mixed partials" check to see if the following differential equation
is exact.
$BR
$BR
If it is exact find a function \(F(x,y)\) whose differential,
\(dF(x,y) \) gives the differential equation. That is, level curves \(F(x,y) = C\) are solutions to the differential equation:
\[ \frac{dy}{dx} = \frac{ $num }{ $den }\]
First rewrite as
\[ M(x,y) \, dx + N(x,y) \, dy = 0 \]
where
\(M(x,y)= \) \{$mp->ans_rule(30) \} ,
$BR
and \(N(x,y)= \) \{$mp->ans_rule(30) \}.
$BR
$BR
If the equation is not exact, enter $BITALIC not exact, $EITALIC otherwise enter in \(F(x,y) \) as
the solution of the differential equation here
\{ $mp->ans_rule(45) \} \(= C \).
END_TEXT

ANS($mp->cmp);

#if ($c==$b-$k) {ANS(str_cmp($Fxy ))}
#else {
# ANS(pc_evaluator([[fun_cmp("C", vars=>["x", "y"], params=>['A','C']), 0, 'This answer cannot be constant'],
# [fun_cmp($Fxy,vars=>["x", "y"], params=>['A', 'C'] ), 1]]) )
#}

ENDDOCUMENT() ;