Second-order derivatives

[Adam Povey]

Apologies if I have missed something: what is the syntax to make d^2y/dx^2 the answer to a question? (In this case, it's part of a derivation of a wave equation.)

At the moment, we use `d^2 y/dx^2` with multi-letter names. This both looks bad in the render and means that `d` can't be a variable elsewhere in the expression. It does, though, work.

In other parts of the course, we use `diff:y/diff:x` to represent first-order derivatives but the syntax for : replacement doesn't permit `diff:^2y`.

I see that `diff(y,x,2)` does render correctly but, when evaluating the expression, it instead calls the diff function that differentiates expressions so the call fails as y isn't an expression.

Thanks,

Adam

[Christian Lawson-Perfect]

I don't think we've done this before, so we have to make a decision!

I think that `diff(y,x,2)` makes the most sense, although it doesn't match what a student would write on paper. To avoid evaluating the diff function, I think you'd have to change the marking algorithm to only do pattern matching, and skip the numerical comparison.

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[Adam Povey]

Right, I shall go work out who marking algorithms work so I can work out which bit to get rid of.

Adam

[Christian Lawson-Perfect]

Here's an example: https://numbas.mathcentre.ac.uk/question/155659/answer-is-diff-y-x-2/

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