Math & Science ⇒ The Identity Matrix

[Cham]

Hi guys,

what symbol are you using for the identity matrix ?

Currently, I'm simply using "I", which appears as a slanted (italic ?) symbol. Everything was fine, until today . I'm not sure any more it's a proper symbol for the identity matrix in complicated equations.

I tried \mathbb{I}, which looks nice too, but I'm now wondering what other options we have for this matrix.

Any other ideas ?

[Stefan Kottwitz]

I would use the same font as for other matrices, i.e. I when I also have matrices A, B, M, etc. all in italic, standard math font.

If there's no other variable, matrix, or map I, i.e. if there's not a chance for confusion, I don't see a reason to change the font. I would not like to have some bold I within non-bold formulas.

Furthermore, there's not just one identity matrix. There's one for each rank, so one should write I_1, I_2, I_3 etc. if the rank or size is not really obvious.

Stefan

[Cham]

Well, it may be a good thing to make the identity matrix to "stand up", against all the other matrices.

Since it's the matrix which "do nothing", it's like "1". Maybe a special font for "1" could be used for the identity matrix. Which one ?

[Cham]

I've found this one :

Code: Select all

\usepackage{bbm} 
\newcommand\bbone{\ensuremath{\mathbbm{1}}}

Very nice, but I'm not sure I'll use it yet...
There are some jaggies on this symbol. It's not smooth at high magnification.


Edit:
This one appears to be nicer :

Code: Select all

\usepackage{mathbbol}

and use \mathbb{1}. Sadly, it interfere with other default symbols...

[localghost]

Code: Select all

\documentclass[11pt]{article}
\usepackage[T1]{fontenc}
\usepackage{bbold}

\begin{document}
  $\mathbb{1}$
\end{document}

Thorsten

[Cham]

Code: Select all

\documentclass[11pt]{article}
\usepackage[T1]{fontenc}
\usepackage{bbold}

\begin{document}
  $\mathbb{1}$
\end{document}

The problem with this solution is it's interfering with the symbols I use for the ensembles (Natural numbers, reals, complexes, etc).

Is there a way to define a "double 1" without calling the bbold package ? Or at least without changing all the other symbols ?

[Cham]

I've found this solution (however, I think the vertical bar is a bit too thick) :

Code: Select all

\usepackage{dsfont}

then use

Code: Select all

\mathds{1}

It's really pretty, despite the thick bar. It may be the best solution yet (?).

I'm pretty sure there's another solution to be found for a double-1.

[localghost]

[…] Is there a way to define a "double 1" without calling the bbold package? […]

Code: Select all

\documentclass[11pt]{article}
\usepackage[T1]{fontenc}

\newcommand*{\id}{{\normalfont\hbox{1\kern-0.15em \vrule width .8pt depth-.5pt}}}

\begin{document}
  \id
\end{document}

[Cham]

Eurk ! This one is extremely ugly. Looks like an hack. The "double-1" is terrible after compilation...

[Cham]

The best solution I've found yet is this :

Code: Select all

\usepackage{bbm}
\newcommand\id{\ensuremath{\mathbbm{1}}} 

But sadly, the symbol resolution is really bad at high magnification. The "1" appears to be pixelised.