Which symbol can be used to refer to identity matrix?
Solution 1:
From Wikipedia:
It is denoted by $I_n$, or simply by $I$ if the size is immaterial or can be trivially determined by the context. (In some fields, such as quantum mechanics, the identity matrix is denoted by a boldface one, 1; otherwise it is identical to $I$.)
It can also be written using the Kronecker delta notation:
$$(I_{n})_{ij}=\delta _{ij}.$$ Hope it helps.
Solution 2:
$I_n$
$I_m$
$I_n = diag(1,1,1,1\cdots,1)$
$(I_n)_{ij} =\delta_{ij}$