math-modesymbols
In math mode, I'm trying to make a square with a diamond in it. My failed attempt has been to put the following in the preamble:
\newcommand{\sqdiamond}{\mathbin{\rlap{$\mspace{2mu}\diamond$}\hbox{$\square$}}}
However, the diamond symbol is not scaled properly relative to the square. I'd like the corners of the diamond to touch the midpoints of the sides of the square, and I can't figure out how to "scale" the diamond appropriately. Is there another way to do this?
\left, \middle and \right actually build two math lists (in each of which \currentgrouptype=16). There can't be a \middle without a corresponding \left and \right, so when you do \left(\right. a later \middle is disallowed. So we have to remember the contents and typeset a \left.\middle|\right. list.
\documentclass{article}
\usepackage{amsmath}
\makeatletter
\def\@BracContents{} % default
\newcommand{\@BracKern}{\kern-\nulldelimiterspace}
\newcommand{\@Brac}[3]{% #1,#3 = left/right bracket type
\begingroup\def\@BracContents{#2}
\mathopen{\left#1\vphantom{#2}\@BracKern\right.}% left bracket
#2% content
\mathclose{\left.\@BracKern\vphantom{#2}\right#3}% right bracket
\endgroup
}
\newcommand{\suchthat}{\nonscript\;{ % open a group
\let\suchthat\@empty % neutralize \suchthat inside \@Braccontents
\left.\@BracKern % fake \left
\vphantom{\@BracContents} % set size
\middle| % bar
\right.\@BracKern % fake \right
}\nonscript\; % end group
}
\newcommand{\bracr}[1]{\@Brac{(}{#1}{)}}% round brackets
\newcommand{\bracc}[1]{\@Brac{\{}{#1}{\}}}% curly brackets
\makeatother
\begin{document}
\begin{gather*}
\left\{x\;\middle|\;x=\frac{1}{2}\right\}\\
\bracc{x\suchthat x=\frac{1}{2}}
\end{gather*}
\end{document}
If you plan to use \suchthat also in a normal \left and \right context, you can do
\newcommand{\suchthat}{%
\nonscript\;
\ifnum\currentgrouptype=16
\middle|
\else
\@suchthat
\fi
\nonscript\;}
\newcommand{\@suchthat}{%
{ % open a group
\let\suchthat\@empty % neutralize \suchthat inside \@Braccontents
\left.\@BracKern % fake \left
\vphantom{\@BracContents} % set size
\middle| % bar
\right.\@BracKern % fake \right
} % end group
}
You can do it, but I strongly recommend you not doing it. You gain nothing in using [ and ] as delimiters for a mandatory argument.
\documentclass{article}
\usepackage{amsmath}
\makeatletter
\newcommand\bmat{{\ifnum\z@=`}\fi\@bmat}
\def\@bmat[#1]{\begin{bmatrix}#1\end{bmatrix}\ifnum\z@=`{\fi}}
\makeatother
\begin{document}
$\bmat[1&0\\0&1]$
\begin{align}
M &= \bmat[1&0\\0&1]
\end{align}
\end{document}
(Note: I have reduced the text width to shorten the output.)
When you understand the trick, you are allowed to use it. :) Hint: look for \eegroup in Appendix D of the TeXbook.
Defining \mat to look for the next token in order to decide a delimiter is, in my opinion, wrong. I'd do like this:
\newcommand{\mat}[2][]{\begin{#1matrix}#2\end{#1matrix}}
so that
\mat{1&2\\3&4} % no fences
\mat[b]{1&2\\3&4} % brackets
\mat[p]{1&2\\3&4} % parentheses
\mat[v]{1&2\\3&4} % vertical lines
\mat[V]{1&2\\3&4} % double vertical lines
\mat[B]{1&2\\3&4} % braces
would do even better, with minimum hassle and better readability.
Personally, I would stick with the long form, but it's a matter of taste.
Best Answer
It is quit difficult to get the two symbols scaled and align correctly in all four math modes. Better draw it using TikZ. One difficulty is to properly scale the size and line width. This can be best done using
amsmath\textmacro. I made two versions which are slightly different.Zoomed:
Variant 1:
Variant 2: