|A problem from derivatives - is there a fix||topic started 10/4/2001; 12:27:37 PM
last post 10/4/2001; 2:08:30 PM
|Arnold K. Pizer - Re: A problem from derivatives - is there a fix
10/4/2001; 2:08:30 PM (reads: 1039, responses: 0)
the answer to this problem is correctly given in the pg code (and in at
least the current version of the problem it looks correct to me --- see
below), WeBWorK using "function_cmp" should accept the correct answer
in any form and reject any incorrect answer. Basically function_cmp
works by evaluating the answer given in the pg code and the answer
input by the student at several "random" points and if these "agree" up
to some tolerance, the student's answer is said to be correct. So a
"non-simplified" correct answer should always be accepted. Sometimes
there can be numerical (floating point) problems. Also the version of
function_cmp distributed with WeBWorK 1.6 had some numerical problems.
I think these mostly resulted in accepting as correct answers that
should have been rejected especially with antiderivatives with a large
constant of integration.|
First check that the answer in the pg code is correct (I assume it is). If you want you can get the current version by clicking on Download WeBWork, Experimental CVS, webwork, ww_prob_lib, ...
Second, check to see if this could be a problem with function_cmp. Backup your copy of PGanswermacros.pl (mv PGanswermacros.pl PGanswermacros.pl.new) and then replace PGanswermacros.pl by PGanswermacros.pl.original (mv PGanswermacros.pl.original PGanswermacros.pl). Then test things.
Note that the correct answer is complicated. It is easy to make a mistake entering answers. The first time I tried this problem, I used "cut and paste" in an attempt to construct the answer: 3(-3 x^2 + 6)^2(-6x) (-9 x^2 + 9)^14 + (-3 x^2 + 6)^3 *14(-9 x^2 + 9)^13*(-18x) but got it wrong (cut and paste gave me (-3 x2 + 6) leaving out the ^). When I fixed this problem, the answer (given above) was accepted.