[WWdevel] parser fun_cmp() error?

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

Hi all,

The following has come up in our on-line homework: I have a problem the 
answer to which is a linear combination of exponentials (e^{-kt} with k 
small).  I'm using the Parser-based fun_cmp() evaluator.  The correct 
answer is marked correct, but an incorrect answer is also.

The correct answer is
   (-201/94)*e^(-t/107) + (295/94)*e^(-t/201)
but the answer
   -e^(t(-1/107 -1/a))+2e^(-t/a)
with a (at least) between 175 and 250 also works.  If a is 300 it doesn't 
work, however.

Is this an accuracy issue?

If you want to see it in action you can see it here:
<https://itcdevel.math.lsa.umich.edu/webwork2b/ma216test/newproblems1/24/>
(logging in as tester1 with password 001 should work).

I'm still checking to see if I can refine it further, but if anyone has 
input on it I'd be delighted to hear it.  I'm using the latest update of 
HEAD from the CVS.

Thanks,
Gavin

-- 
P. Gavin LaRose, Ph.D.  Program Manager (Instructional Tech.)
Math Dept., University of Michigan
gl...@um...                        "There's no use in trying," [Alice]
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http://www.math.lsa.umich.edu/~glarose/  things." "I daresay you haven't had
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