** Using WeBWorK **

It turns out that changes to the code that operates behind the scenes to handle ANS() and the various ans_rule() macros have made a slight change to how these work. In the past, you could use ANS() and ans_rule() in any order (so ANS() could come before ans_rule() if you wanted), but that is no longer true; ans_rule() must come first.

Unfortunately, PGML sometimes did them in the opposite order (in particular, this was the case for MultiAnswer objects). I am attaching a modified version of PGML.pl that fixes the problem, and so works properly with the MultiAnswer object.

If you don't have access to replace this in pg/macros, you can still put it in your course's templates/macros directory, and it will be used instead of the system version.

There are a couple of other issues that I will mention in separate messages.

In addition to the problems with PGML.pl, your problem also pointed out another problem, this time with the Complex object. It turns out that the parentheses in your formula abs(z-($center)) don't get retained properly when the center has a negative complex part. This is due to an error in pg/lib/Parser/Complex.pm. I've attached a corrected version, but you will not be able to use it without having access to the server, as this is not a file that you can override on a course-by-course basis.

If you don't have access to modify and restart the server, you could still work around the problem by making a subclass of the Complex object that overrides the two methods that I have changed. If you need to do that, let me know and I'll show you how.

Edit: There was a typo in the attached file. I have fixed it and uploaded a new copy, so the attached file is now correct.

I have also made a few changes to your problem file to simplify the checker, display the answers better, and make it possible to enter the answers in either order. Here is the modified version:

---

    ##DESCRIPTION
    ##  Find a complex equation for a line in the plane.
    ##ENDDESCRIPTION
    
    ##KEYWORDS("complex", "circle")
    
    ## DBsubject("Complex analysis")
    ## DBchapter("Elementary functions")
    ## DBsection("Polynomials and rational functions")
    ## Date("01/10/2014")
    ## Author("Dave Rosoff")
    ## Institution("College of Idaho")
    ## TitleText1("Geometry")
    ## EditionText1("1")
    ## AuthorText1("Hitchman")
    ## Section1("4.2")
    ## Problem1("1")
    
    ########################################################################
    
    DOCUMENT();      
    
    loadMacros(
       "PGstandard.pl",     # Standard macros for PG language
       "MathObjects.pl",
       "parserMultiAnswer.pl",
       "PGML.pl",
       #"source.pl",        # allows code to be displayed on certain sites.
       #"PGcourse.pl",      # Customization file for the course
    );
    
    # Print problem number and point value (weight) for the problem
    TEXT(beginproblem());
    
    # Show which answers are correct and which ones are incorrect
    $showPartialCorrectAnswers = 1;
    
    ##############################################################
    #
    #  Setup
    #
    #
    
    Context("Numeric");
    Context()->variables->are(x=>"Real",y=>"Real");
    $h = non_zero_random(-10,10);
    $k = non_zero_random(-10,10);
    $r = non_zero_random(1,7); # circle with center (h,k) and radius r
    
    $rsq = Formula("$r^2");
    $circx = Formula("x - $h")->reduce;
    $circy = Formula("y - $k")->reduce; # for nice displaying
    
    Context("Complex");
    
    $center = Complex($h,$k);
    
    $circz = Formula("abs(z - ($center))");
    
    $multians = MultiAnswer($circz, Formula($r))->with(
      checkTypes => 0,
      singleResult => 1,
      separator => " = ",
      tex_separator => " = ",
      checker => sub {
          my ($correct,$student,$self) = @_;
          my ($f1stu,$f2stu) = @{$student};
          my ($f1,$f2) = @{$correct};
          return (1,1) if ($f1 == $f1stu && $f2 == $f2stu) || ($f1 == $f2stu && $f2 == $f1stu);
          return (1,0) if $f1 == $f1stu || $f1 == $f2stu;
          return (0,1) if $f2 == $f1stu || $f2 == $f2stu;
          return (0,0);
      }
    );
    
    ##############################################################
    #
    #  Text
    #
    #
    
    BEGIN_PGML
    Find the complex equation of the circle [`([$circx])^2 + ([$circy])^2 = [$rsq]`].
    Type [`\mathrm{abs}(z)`] for [`\lvert z \rvert`].
    
    [________]{$multians} = [________]{$multians} 
    END_PGML
    
    ##############################################################
    #
    #  Answers
    #
    #
    
    #ANS($multians->cmp);
    
    ENDDOCUMENT();

---

Here, the changes are the following:

1. Use Formula($r) rather than $r so that the student can enter a formula in either one. Without this, the student must answer a number (not a formula) in the second entry. Note that checkTypes => 0 only means that the type doesn't have to be exactly the same type, but can be a compatible one (according to the answer's typeMatch() method). For a Real, the typeMatch() does not allow a Formula, so even with the checkType => 0, you would get a warning about incompatible types, and your checker would not run.

Add separator => " = ", tex_separator => " = " to the MultiAnswer object. Since you are using singleResult => 1 this will change the default separator from a semi-colon to an equal sign, which makes the result look better.

Simplify the logic of the checker. Since you are only doing equality checks (not calling any methods), you don't have to do type checks on the objects. You know that the types will be compatible for equality checking (since that is what typeMatch() checks for you, and your code only runs when the student answers pass that check).

Hope that helps.