Math & Science ⇒ auto {[( )]} brackets macro

[cornail]

Hello,

I am not skilled in programming LaTeX macros, so I ask for your help.
I would like to have a bracket command, e.g. \mybr{ } that automatically
puts the right brackets when writing complex formulas with many level of brackets.
For example:

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$a * \mybr{1 + \exp \mybr{b * \mybr{x - y}}}$

would do the same thing as if I wrote

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$a * \left\{ 1 + \exp \left[ b * \left( x - y \right) \right] \right\}$

but if I remove the innermost brackets (\mybr), it would automatically change to

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$a * \left[ 1 + \exp \left( b * x - y \right) \right]$

.

I couldn't find a package to support this, and I am to unskilled to do it myself. Please help, if it is possible to do this.

Thank you very much!

[Juanjo]

Try the following code:

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\documentclass[a4paper,11pt]{article}

\usepackage{amsmath}

\newcommand{\PutDelim}[4]{%
  \ifcase#1 #3#2#4 \or \bigl#3#2\bigr#4 \or \Bigl#3#2\Bigr#4%
    \or \biggl#3#2\biggr#4 \or \Biggl#3#2\Biggr#4% 
  \else \left#3#2\right#4\fi}
  
\newcounter{DelimLevel}

\newcommand{\br}[2][5]{\addtocounter{DelimLevel}{-1}%
   \ifcase\value{DelimLevel}\PutDelim{#1}{#2}{(}{)}%
      \or\PutDelim{#1}{#2}{[}{]}\or\PutDelim{#1}{#2}{\{}{\}}%
      \or\PutDelim{#1}{#2}{(}{)}\or\PutDelim{#1}{#2}{[}{]}%
      \or\PutDelim{#1}{#2}{\{}{\}}\fi%
   \addtocounter{DelimLevel}{1}}

\newcommand{\setbr}[3][5]{\setcounter{DelimLevel}{#2}\br[#1]{#3}}

\begin{document}

$a * \setbr{3}{1 + \exp \br{b * \br{x - y}}}$

$a * \setbr{2}{1 + \exp \br{b * x - y}}$

\[ z+\setbr{3}{\br{1+\br{n+1}^2}^3-\br{a+\br{b+c}}^2} (c-d) \]

\[ z+\setbr{3}{\br[1]{1+\br{n+1}^2}^3-\br[1]{a+\br{b+c}}^2} (c-d) \]

\[ a_0 + x \setbr{5}{a_1 + x \br{a_2 + x \br{a_3 + x \br{a_4 + x \br{a_5 + a_6 x}}}}} \]

\[ a_0 + x \setbr[2]{5}{a_1 + x \br[1]{a_2 + x \br[1]{a_3 + x \br{a_4 + x \br{a_5 + a_6 x}}}}} \]

\end{document}

As you can see, the macro \br puts a pair of matching delimiters accordingly with its nesting level. The command \setbr also does that, but it has an additional argument to fix the number of nesting levels. It would be nice that such a number could be automatically detected, but I don't know how to do it. I need to fix it a priori. You can get up to six levels. If you need more, you should modify the definition of \br.

Both \br and \setbr have an optional argument to control the size of the delimiter. By default, \br{text} is equivalent to \left delimiter text \right delimiter. If the size automatically chosen by LaTeX is not right, you can add the optional argument: its value goes from 0 (smallest) to 4 (biggest).

[cornail]

Juanjo, you gave me invaluable help in my thesis work, thank you