Special case differentiation operator

[runarberg]

Add \d as a special case differentiation $\rm{d}$ operator.

Input: \d
output: <mo rspace="0">d</mo> with lspace="0" if first in a row.

This will make it far simpler to write differentiation such as:

\df / \dx f(x)

and integrations such as

int f(x) \dx

Where the spacing around the roman $\rm{d}$ is accurate.

[runarberg]

Additionally int f(x) dx could provide the d as an operator text-transformed to italic with rspace="0":

<mo rspace="0">𝑑</mo>

[runarberg]

Arguably roman d as the differential operator—though common—is not standard notation. Perhaps we should value simplicity and cater to standard notation. Users that want to use the roman d can use a font command and space literals for the same effect.

[cben]

Would this preclude using a backslash on any word starting with d?

looks bad because "div" is in regular math font and is ambiguous with "d i v" product;
currently, a backslash helps render it upright as an <mo>div</mo> operator:

But if you special-case \dx etc., would that still work for e.g. \curl but no longer for \div?

P.S. what about partial differential — ∂𝑓/∂𝑥 vs. d𝑓/d𝑥?

[I'm not an active mathup user, just came accross your repo today and am curious about the space of possible syntactic choices, feel free to ignore me]

[runarberg]

@cben Not anymore. I’ve abandoned the special case \d in favor of just trying to be smart about when people write the differential the normal way (i.e. dx). As you’ve demonstrated here a special case \d has pretty bad implications.

The attached PR puts d as an operator if it is a part of a longer term (meaning followed by another alphabetic character), and never if it is preceded with a backslash. If people want the roman d as their differential operator they can actually write rm dx which will yield something like <mo rspace="0">d<mo><mi>x</mi>.

Finally as for writing differentiations (df / dx) the attached PR also puts an lspace="0" if the d is the first letter of a fraction. So df / dx, (del f)/(del x), and rm df / rm dx will all yield the correct spacing. We actually put an lspace="0" to any operator (including ∂) if it is the first element in a fraction or a group. (aside: (\d f) / (\d x) actually puts a space between the d and the operant while del x won’t. This is because—unlike d—the ∂ operator is defined in the MathML operator dictionary to not have any rspace by default).

Thanks for your interest in this repo. I’ve actually been doing a lot of this on my own and it is very nice to get a second pair of eyes and provide some feedback.