identity symbol

[Michael Goerz]

Hi,

I'm trying to get the identity symbol for matrices (number 1 with double
vertical stroke). It's everywhere, and I probably have done it before
myself... but I just can't find it! Any help would be greatly appreciated.

Thanks,
Michael

[Maarten Bergvelt]

Like so?

\documentclass[10pt]{minimal}
\usepackage{dsfont}
\begin{document}
The identity map $\mathds{1}_{V}\colon V\to V$.
\end{document}

--
Maarten Bergvelt

[Michael Goerz]

That looks about right, I'd say from the examples in the package manual.
I don't have the package installed yet... is that really the only way to
go? I see that symbol a lot, it just seems odd that it's only in some
"weird" package.
One example of an article that I was just looking at today, that has the
symbol is this one:
http://arxiv.org/pdf/quant-ph/0110078v1
(Equation 7, e.g.)

Thanks a lot, though.
Michael

[Maarten Bergvelt]

The problem is, I think, that the usual way to get blackboard bold
($\mathbb R$ for the real numbers,etc) only works for capitals, not
for numbers etc. That is why dsfont package was written, I guess.

You can look in the source of most article on the arXive. In this case
the author uses a home grown version of the double stroked identity:

\newcommand{\eins}{\mbox{$1 \hspace{-1.0mm} {\bf l}$}}
--
Maarten Bergvelt

[Kai]

> The problem is, I think, that the usual way to get blackboard bold
> ($\mathbb R$ for the real numbers,etc) only works for capitals, not
> for numbers etc. That is why dsfont package was written, I guess.

That's certainly true for mathbb, but you have (slightly) more luck
with mathbbm.
This one you can use with some few numbers (namely, 1 and 2).

\documentclass{report}
\usepackage{bbm}

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

is maybe what you're looking for?

[Scott Pakin]

See the Math Alphabets table in the Comprehensive LaTeX Symbol List
(http://www.ctan.org/tex-archive/info/symbols/comprehensive/) for various
ways of producing an identity symbol in LaTeX.

-- Scott

[Michael Goerz]

Maarten Bergvelt wrote, on 05/13/2008 10:38 PM:
> On 2008-05-13, Michael Goerz <newsgrou...@8439.e4ward.com> wrote:
>> Maarten Bergvelt wrote, on 05/13/2008 09:25 PM:
>>> On 2008-05-13, Michael Goerz <newsgrou...@8439.e4ward.com> wrote:
>>>> I'm trying to get the identity symbol for matrices (number 1 with double
>>>> vertical stroke). It's everywhere, and I probably have done it before
>>>> myself... but I just can't find it! Any help would be greatly appreciated.
>>> Like so?
>>>
>>> \documentclass[10pt]{minimal}
>>> \usepackage{dsfont}
>>> \begin{document}
>>> The identity map $\mathds{1}_{V}\colon V\to V$.
>>> \end{document}
>>>
>> That looks about right, I'd say from the examples in the package manual.
>> I don't have the package installed yet... is that really the only way to
>> go? I see that symbol a lot, it just seems odd that it's only in some
>> "weird" package.
>> One example of an article that I was just looking at today, that has the
>> symbol is this one:
>> http://arxiv.org/pdf/quant-ph/0110078v1
>> (Equation 7, e.g.)
>
> The problem is, I think, that the usual way to get blackboard bold
> ($\mathbb R$ for the real numbers,etc) only works for capitals, not
> for numbers etc. That is why dsfont package was written, I guess.

Yes, indeed.

> You can look in the source of most article on the arXive.

Wow, I was unaware of that fact. That's really helpful!

> In this case
> the author uses a home grown version of the double stroked identity:
>
> \newcommand{\eins}{\mbox{$1 \hspace{-1.0mm} {\bf l}$}}

Ok, that should work in any case.

Thanks!

[Michael Goerz]

Yeah, that looks great ... and I actually had the package installed already.

Thanks.

[Robin Fairbairns]

magnify that, and it seems to be a superposition of bold "1" and "l"
(not sure whether they're entangled...). the paper certainly doesn't
use any sort of blackboard bold font.

what system are you using? is installation a big deal? (if so, i'll
make a .tds.zip file and put it on ctan, on request.)
--
Robin Fairbairns, Cambridge

[Robin Fairbairns]

that's good, in that the font claims to match computer modern.
however, it's only available as metafont source. hence the
recommendation for doublestroke which is provided as type 1 fonts.
--
Robin Fairbairns, Cambridge

[Michael Goerz]

I'm using Texlive on Suse 10.3. I don't think it would have been a major
problem to install the package, but I wanted to see if I could do
without installing anything new. Also, there was more to do than just
downloading a .sty file and putting it in my texmf tree -- installing an
entire new font with all the bells and whistles seemed like a bit of a
hassle for such a small issue.

Michael