Math & Science ⇒ Reversed cases

[bkarpuz]

Hi all,

I need a new cases environment with the set parenthesis horizontally flipped and on the right-hand side. How is this possible?

Thanks.
bkarpuz

[TheNinjaWizard]

If I understand correctly, I think this may be what you are looking for:
http://www.latex-community.org/forum/vi ... =46&t=5269

[Stefan Kottwitz]

Hi bkarpuz,

you could use a pair \left. and \right\} around an array, similar to the original cases environment, such as

Code: Select all

\left.
\begin{array}{ll}
... & ... \\
... & ...
\end{array}
\right\}

or copy the original cases environment and modify it, if it should really look very similar, regarding alignment and spacing.

Stefan

[bkarpuz]

Thank you Stefan_K.
I could do it as you gave in the codes but I want to learn the way you mention below.
I dont know where I can copy the original cases environment.

Hi bkarpuz,
or copy the original cases environment and modify it, if it should really look very similar, regarding alignment and spacing.
Stefan

Thanks.
bkarpuz

[Stefan Kottwitz]

It may look a bit difficult, since the amsmath package is quite sophisticated. However, here's a short straightforward way:

1. Look for the original code.
2. Copy it in your own document preamble.
3. Replay \def, \newcommand and alike by \renewcommand or \renewcommand* and its syntax. Though you could also stay with \def, it's just TeX, not LaTeX.
4. If there's an @ in that code, use \makeatletter before and \makeatother after.
5. Change the definition as desired.

So, let's get on it.

1. The original code is in amsmath.sty:

Code: Select all

\renewenvironment{cases}{%
  \matrix@check\cases\env@cases
}{%
  \endarray\right.%
}
\def\env@cases{%
  \let\@ifnextchar\new@ifnextchar
  \left\lbrace
  \def\arraystretch{1.2}%
  \array{@{}l@{\quad}l@{}}%
}

2.-4. We need to redefine both macros, since the first contains the left brace, the second contains the right one. The result of the steps in your preamble can be:

Code: Select all

\makeatletter
\renewenvironment{cases}{%
  \matrix@check\cases\env@cases
}{%
  \endarray\right\rbrace%
}
\def\env@cases{%
  \let\@ifnextchar\new@ifnextchar
  \left.
  \def\arraystretch{1.2}%
  \array{@{}l@{\quad}l@{}}%
}
\makeatother

Many lines of code, but it's following the simple steps, the final modification has been just changing \lbrace to . and . to \rbrace.

Stefan

[bkarpuz]

Hi again Stefan_K, I really appreciate what you have shown me.

Thanks.
bkarpuz

It may look a bit difficult, since the amsmath package is quite sophisticated. However, here's a short straightforward way:

1. Look for the original code.
2. Copy it in your own document preamble.
3. Replay \def, \newcommand and alike by \renewcommand or \renewcommand* and its syntax. Though you could also stay with \def, it's just TeX, not LaTeX.
4. If there's an @ in that code, use \makeatletter before and \makeatother after.
5. Change the definition as desired.

...
Stefan

[bkarpuz]

How can I define a new environment rcases (reversed cases) to use both cases and rcases in my codes?

[Stefan Kottwitz]

Define new macros instead of redefining existing. It's very similar:

Code: Select all

\makeatletter
\newenvironment{rcases}{%
  \matrix@check\cases\env@rcases
}{%
  \endarray\right\rbrace%
}
\def\env@rcases{%
  \let\@ifnextchar\new@ifnextchar
  \left.
  \def\arraystretch{1.2}%
  \array{@{}l@{\quad}l@{}}%
}
\makeatother

Stefan

[bkarpuz]

Define new macros instead of redefining existing. It's very similar:

Code: Select all

\makeatletter
\newenvironment{rcases}{%
  \matrix@check\cases\env@rcases
}{%
  \endarray\right\rbrace%
}
\def\env@rcases{%
  \let\@ifnextchar\new@ifnextchar
  \left.
  \def\arraystretch{1.2}%
  \array{@{}l@{\quad}l@{}}%
}
\makeatother

Stefan

Thanks a lot Stefan it seems that we only replace \renewenvironment with \newenvironment and some of the cases with rcases. But I got the following error while running your code.

Code: Select all

! Package amsmath Error: Old form `\cases' should be \begin{cases}.

See the amsmath package documentation for explanation.
Type  H <return>  for immediate help.
 ...                                              
                                                  
l.154     \begin{rcases}

[Stefan Kottwitz]

I see! You also have to change cases to rcases for the call to \matrix@check, modify this line:

Code: Select all

\matrix@check\rcases\env@rcases

Now I remember the mathtools package provides an rcases environment for exactly this purpose. So, instead of our redefinition, loading mathtools is sufficient:

Code: Select all

\usepackage{mathtools}

Stefan