[LON-CAPA-users] adjusting variables on a problem that's been released?

[Mills, Douglas G]

Thank you Gerd!  Good advice.

Doug


On 10/4/11 10:02 AM, "Gerd Kortemeyer" <korte at lite.msu.edu> wrote:

> Hi,
> 
> On Oct 4, 2011, at 10:27 AM, Mills, Douglas G wrote:
> 
>> 
>> 
>> We have an odd situation where in a very small percentage of cases our random
>> variables are working together to generate an impossible answer (³mix 1004.2
>> mL of X and ­4.2 mL of Y to form 1 L of solution...²). The problem has been
>> released and these can be dealt with on a case by case basis as needed if
>> necessary, but we are wondering what would happen if we tweaked the range of
>> one of the variables to eliminate the possibility of the answers over 1000
>> mL.
> 
> All randomizations will change.
> 
>>  Specifically, what happens to students who have already done the problem
> 
> They will keep the credit, but would see a different version of it.
> 
> 
>> with that variable possibly out of the new range (there are several variables
>> involved so only in a very few cases do the calculations result in a solution
>> out of range) -- does Lon-Capa ignore those cases where the problem has
>> already been completed?  What happens if a student has started the problem
>> and so had the values set, but has not completed it ‹ do the original values
>> stay the same even though they are now out of range in the newly published
>> version?
> 
> The values *will* change.
> 
> The only way you can safely address this is to leave everything in place at
> the front of the script block, but then add a section to the end that says
> 
> # everything as it was
> if ($yvolume<=0) { # catch the pathological case
> # completely redo everything in here
>    $xvolume=&random(Š);
> Š
>    $answer=...
> }
> 
> If you do this, only the versions of the problem will change that were
> impossible to solve in the first place.
> 
> BTW, to avoid this situation, I oftentimes first randomly generate the answer
> and then build the problem.
> 
> - Gerd.
> 
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Doug

Douglas Mills
Director of Instructional Technologies
Department of Chemistry
University of Illinois
dmills at illinois.edu
(217) 244-5739