Unknown Math Command

A \command in a math expression is not a known LaTeX math command and was not defined with \newcommand earlier in the same expression, so no writer can render it.

Q-22-1 — Unknown Math Command

A \command in a math expression is not a known LaTeX math command and was not defined with \newcommand earlier in the same expression, so no writer can render it.

What this means

Math is written in LaTeX syntax, and every \name must be a command quarto-math knows (the standard LaTeX and amsmath math commands, plus the macros the expression defines with \newcommand). This error fires when a command is neither. The diagnostic underlines the command; the rest of the expression is still parsed, but the whole equation is emitted verbatim as source text in formats that need a conversion (Word), because half-converted math would be worse than none.

Why this happens

Common causes: a typo (\aplha), a command from a LaTeX package that has no math meaning (\textsuperscript), a document-level macro defined in a LaTeX preamble that this expression cannot see, or a control sequence that is not standard at all (\R for the reals).

How to fix it

Fix the spelling, replace the command with its standard equivalent (\mathbb{R}), or define it in the expression: \newcommand{\R}{\mathbb{R}} x \in \R. HTML output through MathJax or KaTeX may still render an unknown macro if that engine defines it; this error is about the converters Quarto runs itself. Under html-math-method: mathml it is reported as a warning: the expression is left as TeX and MathJax is loaded for the page so it still renders.

Where it is reported

Math diagnostics point into the .qmd at the exact characters inside the $…$ or $$…$$ block, including math that spans several lines or sits inside a block quote or list item. When a \newcommand macro is involved, a problem inside the macro body points at the definition and a problem in a macro argument points at the use.