Numbas Open Resource Library submissions in Numbas Open Resource Library

Good point. I've added a "needs attention from the reviewer" tag.

PS: I can't tag it as "back to reviewer" or something, so not sure how/when/how efficiently it is caught that some things have been addressed?

It took me a while to see that someone had commented on this: is there an option to email the submitter when they have to do something?

I have addressed:

Metadata

• name changed (though I would have thought "only the purpose of the item" was already satisfied, your comment seems to imply a stricter rule than you have asked for in the guidance)
• variables grouped and explained
• gaps named

Text

• (I don't agree with the \mathrm{A}, in pure maths, just \(A\) is totally standard notation.)
• evalues and evectors all changed to eigenvalues and eigenvectors
• Advice updated.

Structure

• Split characteristic polynomial from eigenvalues. Though I'm a little bit sceptical about this... I originally wanted it on the same page, because once you've worked out the char poly, you can just read off the eigenvalues (if you've factorised it), and now you have to click back to the previous part again to see them.
• Added end point.
• Selected "show next part when answer is correct". Though of course in "real life" (i.e. when doing it on paper), working out the eigenvector and getting 0 is a good check that one has the wrong eigenvalue :-)

I have not addressed (yet)

• linalg2 extension: need to talk to my colleague who made it, or look into the official linear algebra extension to see if these functions are there as well. This might take me a while. Or might you (Christian) help me to merge in just some of those functions which we find so useful in this kind of question?
• I don't really agree with splitting the eigenvector part in two and giving "show expected answer". One point is that any multiple of the eigenvector is also correct, and in general (for bigger matrices, where you might have a 2-dimensional eigenspace) any basis for the eigenspace. And my marking algorithm accepts all such correct answers. And the other is that I want the question to look the same for other versions, e.g. 3x3 or higher, where there might be a different number of eigenvalues for which one has to find eigenvectors. In my mind, the point here is that you can reuse this part to find eigenvectors for any eigenvalue, and so you don't have to rewrite it again and again. (PS: I'm working on and planning to submit "equivalent" questions for 3x3.)

Questions

• One of the check boxes is "correct and incorrect unit tests for each part". I don't really know how to do that, and you didn't mention it... I have checked the marking (by hand) quite a bit.
• One of the check boxes you have not checked is "no references to external sources". I don't have any, do I?

• The name should describe the activity. "Find the characteristic polynomial, eigenvalues and eigenvectors of a $2 \times 2$ matrix" would do.
• The linalg2 extension needs to be published, or merged into the official linear algebra extension.
• The variables need descriptions, explaining what they represent.

• Optional: Being very pedantic, I would use \mathrm{A} for a matrix.
• The label on the next part link to enter more eigenvalues should be "Find eigenvectors for a different eigenvalue". At the moment, it's "Find evectors for a different evalue".
• In the advice, there are some paragraph breaks in the middle of sentences. Did you want display-mode maths? If so, use \[ and \].
• I needed a bit more detail on producing the eigenvectors once I'd got the reduced row echelon form of $A-\lambda I$.
• Typo in the advice: "for a given eigenvalues".

• The first part could be split into two parts - you have to compute the characteristic polynomial in order to get the eigenvalues.
• The eigenvectors part could also be split in two, so that you can turn on "show expected answer" for the eigenvectors input, since the eigenvalue will be fixed.
• The question doesn't have a well-defined end point. There could be an option labelled "I have given all the eigenvectors" which goes to an information-only part, giving some feedback about whether that was true?
• The option to move on from the first part should only be shown once the student has given the correct eigenvalues. Similarly with moving on from the eigenvectors part.

I'm reviewing this.