CustomAnswerCheckers
Custom Answer Checkers: PG Code Snippet
This is the essential PG code to write problems that check "arbitrary" conditions on the student's answer.
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PG problem file | Explanation |
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DOCUMENT(); loadMacros( "PGstandard.pl", "MathObjects.pl", ); TEXT(beginproblem()); |
Initialization: Standard. You might want to use answerCustom.pl, although it is not necessary. |
Context("Numeric"); $ans = pi/3; $val = cos($ans); |
Setup: To set up the custom answer checker we will override the answer checker routine for the MathObject that we're using to check the answer. Thus our answer object should be of the same type (e.g., Real, Formula, etc.) as what we want the student to be entering. For example, here we're going to ask for a value of x such that cos(x)=cos($ans). Thus we set up the answer to be a real number.
In this sample, we've taken advantage of a bunch of overloading that MathObjects do: the line
Similarly, |
Context()->texStrings; BEGIN_TEXT Enter a value of \(x\) for which \(\cos(x) = $val\): \(x = \) \{ ans_rule(25) \} END_TEXT Context()->normalStrings; |
Main Text: We don't have to make any changes or additions to the text section of the file. |
$showPartialCorrectAnswers = 1; ANS( $ans->cmp( checker=>sub { my ( $correct, $student, $ansHash ) = @_; return cos($correct) == cos($student); } ) ); ENDDOCUMENT(); |
Answer Evaluation:
Then when setting up the answer and solution section, we override the default answer checker in the answer. The replacement is a Perl subroutine that takes as its arguments the correct answer, student answer, and answer hash that is being processed in the answer comparison. Its return value should be 1 if the student's answer is correct, and 0 (false) otherwise. When doing the relational check, you should always put the correct answer on the left and the student answer on the right, e.g., We could also specify the answer checker as a separate subroutine by writing sub mycheck { my ($correct, $student, $ansHash) = @_; return cos($correct) == cos($student); } ANS( $ans->cmp( checker=>~~&mycheck ) ); (The
We can set an error message in the answer checker by using sub mycheck { my ($correct, $student, $ansHash) = @_; Value->Error("Try again") if cos($student)==sqrt(3)/2; return cos($correct) == cos($student); } ANS( $ans->cmp( checker=>~~&mycheck ) ); To see all of the keys and values in the foreach my $key ( keys %{$ansHash} ) { warn "key: $key, value: $ansHash->{$key}"; } |
- POD documentation: answerCustom.pl
- PG macro: answerCustom.pl