Pairs of numbers incorrectly concatenated with cdot = false

[kapple19]

I initially opened this issue in Symbolics.jl since I superficially noticed this issue occurs with @variables and not Exprs or Strings fed to latexify.

Basically the @latexrecipes defined in Symbolics.jl/src/latexify_recipes.jl all set cdot --> false, which avoids placing \cdots everywhere.

There isn't a simple solution to this, but I'm happy to look into the challenge of designing an algorithm and non-breaking (additive) API that places \cdots in some nicely disambiguating places.

[gustaphe]

Interesting.

To simplify the problem description a little:

julia> @latexify 2x + 2*3 cdot=false
L"$2 x + 2 3$"

$$2x+23$$

should be

"$2 x + 2 \cdot 3$"

$$2x+2\cdot 3$$

Since the current representation is incorrect, this is a bug. I don't think the solution has to be technically non-breaking.
If you can think of a good heuristic to solve this, I'd be happy to merge it.

[ChrisRackauckas]

Why not use parenthesis?

[gustaphe]

Why not use parenthesis?

For one thing I think that's an even harder algorithm to implement.
And it's my understanding cdot=false is used for aesthetic reasons, and then $3(2)$ is no better than $3\cdot 2$ in my opinion.

I'm toying with one idea where a step of str = replace(str, r" \\cdot (?![0-9])"=>" ") is added to multiplication in latexoperation if cdot is false.

julia> @latexify 2x+2*(3)+2*3^4+3^4*2+x^4*x cdot=false
L"$2 x + 2 \cdot 3 + 2 \cdot 3^{4} + 3^{4} \cdot 2 + x^{4} x$"

$$2x+2\cdot 3+2\cdot 3^4+3^4\cdot 2+x^{4}x$$

This catches many of these things, but it's not perfect. For instance, I would expect $(3u"cm")*x to be $3\mathrm{cm}\cdot x$ rather than $3\mathrm{cm}x$. But that would basically require a separate vector like prevop, and that system is difficult enough.

[kapple19]

It'll also be a battle of preference between users. Right now we have set_default (iirc) with the option to set cdot = true or false, and my idealistic mind is imagining some more specific options that users can tweak such as whether to represent multiplication as a space, a dot, parentheses (very tricky as noted above) or even other things, maybe user-inputable, e.g. \times.

On tip of that, I'm (again idealistically) imagining users can specify which multiplication presentation to use for different contexts, e.g. between two numbers, between two symbols, between a number-then-symbol, or between a symbol-then-number (I haven't checked if Latexify aleays places numbers first), or even as your example, number-with-units-then-symbol.

And yes, such a change doesn't need to be API breaking, and my (again idealistic) mind might be motivated enough to come up with an algorithm for this, or at least a simpler improvement. I'll try out some things and give it a shot. Also a nice challenge yet introductory experience to more complicated contributions into the Julia ecosystem. That said someone else might have a better solution.

Edit: My brain misprocessed the double-negative in your statement about breaking changes. I'll see what I can do with the current API and whether we'll need a breaking change or not - I imagine we will need to break things.