Here is my first contribution:

I have included a XML file
Speaking in general, the site archive.moodle.net has collections of quiz questions which people can use and adapt. And you are welcome to create an account and share your XML file in the community Sharable quiz questions on our new sharing site Moodle.net
Great! I'd be happy to participate, and post examples. I have been creating a solid set of problems of various degrees of complexity for my Linear Algebra class.
So far I have been making formulas problems for an old version of Moodle. My school is working on updating to the latest version sometime next year. I noticed that one of the problems of mine that you posted doesn't quite display correctly. I can only assume that this is because it was created for the older version of Moodle. Should I wait for the new version before I participate? I don't want my contributions to look subpar.
e.g. on my edition of Moodle these look good
but I don't know how they will look on the current version. Is there anyway to try them out on a current version?
Here is a question for the Moodle Formulas question bank. Probably for the category Matrices and Vectors.
I included annotations for the variable selections ( I used the pick function to pick from a pre-selected collection of 56 vectors (to keep the numbers small and the matrices nice),
and for the grading formulas ( For example: if a line is asked for, like 3 x + 4 y = 15, it also counts .75 x + y = 3.75 correct, and gives partial credit for 3 x + 4 y = 0 etc. I use the round function round(_1,4) to 4 decimals, since I require my students to round to least 4 decimals).
Here is what it looks like:
Thanks Dominique, looks great. I'll submit more.
I am not quite sure why my pointing out that the problem shown in the question bank did not quite look like the problem I submitted, indicated that I was in anyway offended. I was merely pointing out that it was different: a line was repeated several times. I see it has been corrected now. Great.
I am familiar with editorial stylistic preferences. Most editors in mathematical journals though do use TeX for all text as well, so as to guarantee a uniform look. Having formulas and text in different fonts is usually frowned upon. In all my publications I use TeX for text and formulas as well as in pictures.
Thanks for the info. I started learning Moodle formulas this summer. And have been very frustrated with the lack of instructions for it. I was always puzzled why the interface didn't have a font and font-size button. It only has these choices
So at first I ended up with ugly looking text and beautiful TeX-ed formulas. The work around for me was to use \ text{ } so that everything looks uniform. The more I learn about formulas, the more I realize, that you really need to know HTML, CCS and Java script. At first the Formulas Plugin looks like it has an interface that can be used by anybody without that skill set. It is like getting a car and first thinking that you can just drive it, and then finding out that you are are actually expected to be a car mechanic too. It would be great if there was an owner's manual. It seems to me that all information is scattered over forum posts, and several moodle sites. I find it very hard to locate anything when I need it. That's why I asked if we could start building a larger problem bank so that we would have a resource for future users. Now I also think we should start building a better instruction manual. It would have been nice if I had known about lots of stuff that I had to discover and figure out the hard way. Just as you, we all have time constraints. I am teaching full time and with covid our school went online. I have been spending my time...full time, including weekends...trying to convert all the problem sets for my classes, and the tests, the quizzes and labs to Moodle Formulas in a few months (and they were all beautifully done in LaTeX, and in PDF form and had been created over many years of teaching) . And I must say I love Moodle Formulas: I love the randomization, the instantiation, the ability to check problems, insert and check answers, and create almost all the questions I would want to create (up to a point) ... and the fact that Moodle can grade things instantaneously. But in the beginning most of my time went into trying to figure out how to do things. For example how to create nice inline matrices with answer fields, how to place radio buttons where you need them, how to deal with partial credit, how to get TeXed formulas in multiple choice answers etc. It would have been great if I had known about how to change the font, three months ago. And of course you probably know a reference to it and can give me a link. But what I would really want is a manual, or even just a beginner's manual. I know there is 'some' stuff online, but it is sketchy and sometimes just not clear. Only after months of figuring something out I re-read some of the 'instructions' and think, 'oh that is what they meant' and 'why didn't they say so?", or "give an example'. The forum is a big help ... but not ideal either. It is great that there are knowledgable people there who are willing to help, but sometimes they too seem frustrated with answering the same questions, or can get irritated if you don't know something that they have known for years. It would be great if all that knowledge could be posted as a manual. Lots of people could contribute short instructional modules about everything (including examples). With so many knowledgable Moodle formulas experts each contributing a one paragraph instruction module, we could create a great online manual in a couple of years ... just a thought.
Anyway, Dominique, thanks for your help these last few months. I really appreciate it. I have learned a lot. Au revoir!
By the way, I do want to thank you for all the changes you have made to the moodle formulas site the last few months. It has improved tremendously. Thanks!
Here is an example of the use of the
join str and pick functions
to avoid fractions like 1/-1 and 1/1
In those cases we don't want to use the \ dfrac{ }{ } TeX function
It would be much nicer to have instead
or
and in case of a regular fraction
Here is the code using join, pick and str
I have included an XML file.
(Of course this is not a particularly interesting example of a quiz problem; but it is intended to illustrate an interesting example of how to use the pick str and join functions [in avoiding 1/1 and 1/-1].)