Stack Feedback changes values

Stack Feedback changes values

by Bertrand Rousset -
Number of replies: 7

Hello,

I made a test with the variables:
n1:rand(4)+1;
 n2:rand(3)+ 2;
 pol:expand((z-n1-n2*i)*(z-n1+n2*i));
 sol:{n1 + i*n2, n1 - i*n2};
The student has to solve the equation : \[{@pol@} = 0\]
The correct answer is sol

During the test, they can't see the feedback. They can see the feedback one day after. When the students have the feedback with the correct answer, Stack has changed the values of n1 and n2. So, if a student has indicated a correct answer, his solution is considered as wrong because n1 and n2 has changed. 

Could you tell me please how to solve this problem? Thanks

Best wishes

Bertrand
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In reply to Bertrand Rousset

Re: Stack Feedback changes values

by Tim Hunt -
Picture of Core developers Picture of Documentation writers Picture of Particularly helpful Moodlers Picture of Peer reviewers Picture of Plugin developers
That should not happen. We store the seed when the question starts, and that should fix the values of all the randomised numbers.

I guess if the question was edited singificantly (e.g. removing or adding rand() calls) after students had attempted it, then you might see this, so don't do that.
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In reply to Tim Hunt

Re: Stack Feedback changes values

by Bertrand Rousset -

Dear Tim,

Thanks for your message. We have 1 700 students who made the test during this week-end. So do you think it could be what you call "the question was edited significantly"?

A student explained me that during his moodle session, after answering a question the values of randomised numbers changed before ending the test. It is due to a problem with moodle?

Bertrand

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In reply to Bertrand Rousset

Re: Stack Feedback changes values

by Tim Hunt -
Picture of Core developers Picture of Documentation writers Picture of Particularly helpful Moodlers Picture of Peer reviewers Picture of Plugin developers
I really don't know what might be causing it. We have hand students answer millions of questions here at the Open University, and I have never received a report like this.

To understand what is going on, we would need lots more details: exactly which version of STACK and Moodle. How is it installed (Maxima version, and settings on the STACK admin screens). can you come up with a reliable way to reproduce the problem. (E.g. create a quiz wiht a quesiotn like this. Start attempt. Type this, click that, etc. ... observe numbers changed.)
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In reply to Bertrand Rousset

Re: Stack Feedback changes values

by Christopher Sangwin -
Picture of Particularly helpful Moodlers Picture of Plugin developers

I'm sorry you've had this problem.

To replace the STACK quizzes in Edinburgh we would need > 6000 hours of marking time per year now.  The only time this has happened is when a teacher edited the question.  I'm keen to track down what has happened, so as Tim suggested, please send us information.  Email to me, C.J.Sangwin@ed.ac.uk if you prefer to avoid a public forum.  We will help.

Chris

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In reply to Christopher Sangwin

Re: Stack Feedback changes values

by Bertrand Rousset -

Dear Chris, Dear Tim,

Thanks for your help. I'll send you more information.

Bertrand

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In reply to Christopher Sangwin

Re: Stack Feedback changes values

by Bertrand Rousset -
Dear Chris,

Thanks for your message. It seems to be due to the moodle's "memory cache" (I hope it's the good translation). The admin used an enhanced memory cache. They have changed this memory cache. They have put the usual cache and now it's ok.

Bertrand
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In reply to Bertrand Rousset

Re: Stack Feedback changes values

by Christopher Sangwin -
Picture of Particularly helpful Moodlers Picture of Plugin developers

Thank you for confirming the cause.  I'm sorry you had this problem.  Thank you for reporting it, as it is useful to know what can cause unexpected problems.

Chris

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