Matrix answer invalid for any input

[vohonen]

I'm a head TA at a Matrix Algebra course that runs on the MyCourses platform and has a STACK question on matrix multiplication. I could see from the question settings that the question was made in 2015 and has been assumedly used in each yearly course iteration since. I certified from last year's head TA that there was no issue in the previous iteration. However, this time the question throws an error message that the input is invalid:

Again, this was working at least last year and assumedly for almost ten years. A similar question with matrix multiplication on the same quiz with similar options works without throwing an error. In that subsequent question, the text after the answer "Your last answer was interpreted as follows: matrix([37,47],[27,20],[55,24])" formats the matrix in TeX fashion. The input type and answer is obviously a matrix for both questions.

I cannot infer much from the docs because they don't mention this kind of behaviour for a matrix input. Any help on how to proceed?

[sangwinc]

OK, if you email me the question to C.J.Sangwin@ed.ac.uk, and confirm which version of STACK you're running, I'll take a look. Chris

[aharjula]

Chris,

This is a thing related to forbidden words that broke in last summers update, and does not seem to propagate fast enough through our course staff...

I think there is an issue already, but cannot at this moment remember it (not an issue here but in Zulip). In any case, previously one could have matrix as a forbidden word for a matrix input to stop anyone doing stuff with matrices inside the cells of that input, now however, the forbidden words are not applied cell by cell but instead on the whole input value which is obviously a matrix and thus always invalid if one has that forbidden word defined.

[sangwinc]

@vohonen thanks for emailing me your question. In that question you don't have "matrix" in the forbidden words for the input, so I don't think that's the problem.

I can't reproduce the invalidity, so I'm not sure what's going on with this.

(Also, just a reminder. Please could you add question tests and deploy variants? https://docs.stack-assessment.org/en/Authoring/Deploying/ It makes tracking down problems a lot easier.)

[aharjula]

Chris,

Had a chat with the reportter, they managed to fix the question by removing the forbidden word and did not notice that they were testing still with the old version thus sending you the fixed one, Moodle and versions is too easy. In any case, this is a real issue and affects many old materials and did indeed crop up this summer.

Here is a minimal question, simply a matrix input with matrix in the forbidden variables, fails with about week old dev:

Matrix forbidden-words.xml.txt

[sangwinc]

Thanks @aharjula, let's try to get a fix for this into the next release. I'll have a look.