6

$I$ is commenly used as a notation of identity matrix. I am wondering is there any notation else for identity matrix?

aban
  • 215
  • 3
    $\text{Id}$ is also common. – JimmyK4542 Jan 06 '17 at 03:26
  • 1
    I have seen the use of $I_d$ to denote a $d\times d$ identity matrix. As an added comment to JimmyK4542's, you may also see the more explicit notation $\operatorname{id}_V$ where $V$ is the relevant vector space. – parsiad Jan 06 '17 at 03:27
  • 4
    In some contexts, I have also seen a doublestrike $1$, similar to the difference between $N$ and $\mathbb N$, in order to emphasize that it is the compositional identity. The fact that I am unable to type it in mathjax right away however should imply something about how uncommon that notation is though. – JMoravitz Jan 06 '17 at 03:29
  • I use \mathds{1} to get the double strike 1 (aaah so lovely) but the dsfont package isn't a default. Picked it up from some random lecture notes from someone at EPFL and liked it. – Squid Jan 06 '17 at 03:49
  • 2
    More rarely now, but at some point $E$ was used for the identity. – copper.hat Jan 06 '17 at 05:34
  • 2
    @copper.hat: $E$ is sometimes used in German (Einheitsmatrix), and also in my native Swedish (enhetsmatris). – Hans Lundmark Jan 06 '17 at 06:36
  • @HansLundmark: Thanks, that makes sense! – copper.hat Jan 06 '17 at 06:37
  • @copper.hat that is cool~ definitely what i want :) – aban Jan 06 '17 at 08:51
  • 3
    $1, , ,\mathbb{1}, , ,\mathbf{1}, , ,\operatorname{I}, , , \mathbb{I}, , ,\mathbf{I}, , ,\operatorname{Id}, , ,\operatorname{id}$ and anyone of these could be equipped with an index $n$ or not. – Marius S.L. Jun 07 '21 at 19:19

4 Answers4

3

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.

Alex Mathers
  • 18,509
2

You could also use a "double one" like this: $\mathbb{1}$. To write it in LaTeX, you can import the package dsfont and then use \mathds{1}. You can also import bbold and then use \mathbb{1}, but this will change the appearance of your other \mathbb commands.

Arducode
  • 66
1

$I_n$

$I_m$

$I_n = diag(1,1,1,1\cdots,1)$

$(I_n)_{ij} =\delta_{ij}$

Fawad
  • 2,034
1

You can use the notation $\mathbb{I}$ written using this code \mathbb{I}

SPARSE
  • 442