I have never seen that notation, could you give the tile and author of the text you're using in that class?1. A matrix is denoted by a letter e.g. A with a line underneath (can't really show on here easily) but what is meant by A with a double underline?
Is it something like or ? If it's one of these, it usually means an matrix with real entries.E (as in "is an element of") R^nxn
The R is a very ornate looking letter, a bit like old calligraphy. Very odd.