### From WeBWorK

# NAME

bizarroArithmetic.pl - Enables bizarro arithmetic where, for example, 1+1 does not equal 2; Useful for checking the form of an answer, as with factored polynomials and reduced radicals.

# DESCRIPTION

The point of this technique is to catch answers in unsimplified forms. A custom answer checker is generally used in which the student answer is first checked against the correct answer via regular arithmetic. Then one or more of the bizarro arithmetic flags should be set, and the two answers should be compared again.

The bizarro arithmetic is basically defined as:

a bizarro+ b = f(g(a) regular+ g(b))

where f and g are inverse functions defined on all of R, and are odd functions. There is also bizarro-, bizarro*, bizarro/, and bizarro^. f(x) = x^3+3x is a good choice for f.

To enable the bizarro arithmetic operators, load this file with the macros, and then use any subset of:

Context()->operators->set( '+' => {class => 'bizarro::BOP::add', isCommand => 1}, '-' => {class => 'bizarro::BOP::subtract', isCommand => 1}, '*' => {class => 'bizarro::BOP::multiply', isCommand => 1}, ' *' => {class => 'bizarro::BOP::multiply', isCommand => 1}, '* ' => {class => 'bizarro::BOP::multiply', isCommand => 1}, '/' => {class => 'bizarro::BOP::divide', isCommand => 1}, ' /' => {class => 'bizarro::BOP::divide', isCommand => 1}, '/ ' => {class => 'bizarro::BOP::divide', isCommand => 1}, '//' => {class => 'bizarro::BOP::divide', isCommand => 1}, '**' => {class => 'bizarro::BOP::power', isCommand => 1, perl=>undef}, '^' => {class => 'bizarro::BOP::power', isCommand => 1, perl=>undef}, );

At this point the arithmetic operators will still be behaving as normal. Turn on the bizarro arithmetic with:

Context()->flags->set(bizarroAdd=>1); Context()->flags->set(bizarroSub=>1); Context()->flags->set(bizarroMul=>1); Context()->flags->set(bizarroDiv=>1); Context()->flags->set(bizarroPow=>1);

Sample usage

This will check if a student has simplified according to the rules of division, for example, assuming that $ans = Formula("2x^2"),

2 x^4/x^2

will be rejected, as will

4/2 x^2

ANS($ans -> cmp(
checker=>sub{
my ( $correct, $student, $ansHash ) = @_;
return 0 if $ansHash->{isPreview} || $correct != $student;
$student = $ansHash->{student_formula};
$correct = $correct->{original_formula} if defined $correct->{original_formula};
$student = `Formula("$student")`

; $correct = `Formula("$correct")`

;
return 0 unless ($correct == $student);
Context()->flags->set(bizarroDiv=>1);
delete $correct->{test_values};
delete $student->{test_values};
my $OK = (($correct == $student) or ($student == $correct));
Context()->flags->set(bizarroDiv=>0);
Value::Error("Your answer is correct, but please simplify it further") unless $OK;
return $OK;
}));