[WWdevel] interval_cmp

[P G. L. <gl...@um...>]

Hi guys (esp. John),

I have a question about the behavior of interval_cmp (from John's 
extraAnswerEvaluators.pl macro file).  I'm using it in a brutally 
unintended way, which may explain why I am (or it is) confused.

In a calculus problem, I want students to find critical points and 
indicate if they correspond to maxima, minima, or neither.  And I don't 
want to give away in advance how many points there are.  So I was trying 
to coerce interval_cmp to do this for me by having it evaluate a set of 
"intervals," viz.,
   interval_cmp( "(-2,min),(3,max)", 'unions'=>'no',
 		'strings'=>['none','min','max','neither'] );

This works very well, until there is no maximum (or no minimum), in which 
case
   interval_cmp( "(-2,min)", 'unions'=>'no',
 		'strings'=>['none','min','max','neither'] );
has trouble: as student entering (-2,min) has her/his answer marked wrong 
with the message "The parentheses for your list should be removed." 
Removing the parentheses works if the interval_cmp call is changed to
   interval_cmp( "-2,min", 'unions'=>'no',
 		'strings'=>['none','min','max','neither'] );

So I guess I have a couple of questions.  Or three.
  1. Have I overlooked a better way of checking this type of problem?
  2. Is there some feature of interval_cmp that I can change to get a more
     intuitive (at least from the perspective of a student) behavior?
and/or
  3. Is there an easy tweak to interval_cmp that will have the same effect?

Thanks, and Happy New Year,
Gavin

p.s. I also have a problem where I want to check the answer 
"(0,min),(a,max)", where a is a constant.  My rather coarse solution was 
to copy the interval_cmp evaluator into the problem, calling it 
my_interval_cmp, and add the variable 'a' to the Parser Context.  Is there 
a better way of doing this?

-- 
P. Gavin LaRose, Ph.D.  Program Manager (Instructional Tech.)
Math Dept., University of Michigan
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