How to use \mathcal with subscript? Undefined control sequence..

Question

I am trying to have a cursively written l (L) with a subscript A. I tried this:

If A has a straight line $\matchcal{l\subscript{A}}$

But I'm getting undefined control sequence. Why is this?

Answer 1

You realize you're using \matchcal instead of \mathcal? If your code snippet is wrong, please provide the correct piece of code, otherwise we just have to guess.

But I suppose you're looking for \mathcal{l}_A or \ell_A.

Undefined control sequences occur when LaTeX encounters something it doesn't know, such as a typo.

Answer 2

Since only the letter is in mathcal mode, you want \mathcal{l}_{A}

If you wanted an ell with a mathcal A subscript, it would be \ell_{\mathcal{A}} for a "cursive" ell, or l_{\mathcal{A}} for a regular math-italic ell with a caligraphic subscript.

For both, you would want to specify the caligraphic font separately in the "body" and "subscript". Thus, for example, \mathcal{A}_{\mathcal{B}}.