What is this stylish R-like symbol?

Question

What is that stylish R-like symbol at the end of the statement? I combed the lists of linear algebra symbols from almost every source online. Some guesses were Row space (which might make sense, just that I can't find any sources) and Rank (which doesn't make any sense...)

The book is Sliding Mode Control: Theory And Applications (by Christopher Edwards and Sarah Spurgeon) page 37.

Answer 1

$\mathcal R(A)$ is not an uncommon notation for the row space of $A$. Neither is just $R(A)$. I'm not sure which sources you're consulting, but I've seen both.

However, the ultimate authority on notation is the textbook itself. If you go to p. 207 of the textbook (A.1 Mathematical Notation in the table of contents), you see the line

$\mathcal R(A) \quad$ the range space of the matrix $A$ (viewed as a linear operator)

and so that's what it is. You might be more used to saying "column space" instead of "range space".