1

I have the following code, where I have multiple cases and all need to be labelled. I tried using subnumcases, however I wanted some freedom in labelling (the $k^{th}$ case must be labelled C.k etc), which I could not achieve when using that custom package. I also tried to use two alignment tabs, using alignat, but that does not work inside cases environment.

When I tried to label manually, the labels are not right-aligned, and as such they appear odd. Is it possible to at least right align the manual equation labels? Or is there an elegant way to present these equations?

\documentclass[a4paper]{article}
\usepackage{geometry}
\geometry{left=1in,right=1in,top=1in,bottom=1in}
\usepackage{amsmath, amsfonts, amssymb, bbm, cases}

\begin{document}
 \begin{align*}
f(x) =
 \begin{cases}
   x_1, & \text{if } x\in(\sum_{i=1}^n b_i\log(a_i/b_i)-(\sum_{i=1}^n b_i) \log(a_1/b_1),\infty),\quad \text{(C\textsubscript{1})}\\
  x_2, & \text{if } x\in (\sum_{i=2}^n b_i\log(a_i/b_i) -(\sum_{i=2}^n b_i) \log(a_2/b_2), \\ & \sum_{i=1}^n b_i\log(a_i/b_i) -(\sum_{i=1}^n b_i)\log(a_1/b_1)),\quad \text{(C\textsubscript{2})} \\
   & \vdots \\
   x_k, & \text{if } x\in (\sum_{i=k}^n b_i\log(a_i/b_i) -(\sum_{i=k}^n b_i) \log(a_k/b_k), \\ &\sum_{i=k-1}^n b_i\log(a_i/b_i) -(\sum_{i=k-1}^n b_i)\log(a_{k-1}/b_{k-1})),\quad \text{(C\textsubscript{k})}\\
   & \vdots \\
   x_n, & \text{if } x\in (0, \sum_{i=n-1}^n b_i\log(a_i/b_i) -(\sum_{i=n-1}^n b_i) \log(a_n/b_n)),\quad \text{(C\textsubscript{n})}.
 \end{cases}
\end{align*}
\end{document}
  • 2
    See the empheq package, I think it is even an example in the manual. Btw: you have an error, there is no A4 class option it us called a4paper – daleif Jun 21 '16 at 16:35
  • Off-topic: \geometry{left=1in,right=1in,top=1in,bottom=1in} may be written more succinctly as \geometry{margin=1in}. – Mico Jun 21 '16 at 16:53
2

The following sets up a specific numcases environment to have the sequential numbering C1, C2, Ck, Cn using \setupnumcases. The setup is restored using \restorenumcases.

The idea is to update \theequation - the macro responsible for setting the equation counter or representation - to set a specific list of possibilities in sequence. This sequence is dictated by \thesaveeqncntr, which is used in place of \theequation.

enter image description here

\documentclass{article}
\usepackage[margin=1in]{geometry}% Just for this example
\usepackage{amsmath,cases}

\newcounter{saveeqncntr}
\renewcommand{\thesaveeqncntr}{\ifcase\value{equation} % 0
  \or $C_1$ % 1
  \or $C_2$ % 2
  \or $C_k$ % 3
  \or $C_n$ % 4
  \else ? % 5+
  \fi}%
\newcommand{\setupnumcases}{%
  \setcounter{saveeqncntr}{\value{equation}}% Store equation counter
  \setcounter{equation}{0}%
  \let\theequation\thesaveeqncntr}
\newcommand{\restorenumcases}{%
  \setcounter{equation}{\value{saveeqncntr}}% Restore equation counter
  \renewcommand{\theequation}{\arabic{equation}}%
  \ignorespaces}

\begin{document}

An equation before
\begin{equation}
  f(x) = ax^2 + bx + c.
\end{equation}

Some text before.%
\setupnumcases
\begin{numcases}{f(x) =}
  x_1, & if $x \in (\sum_{i=1}^n b_i\log(a_i/b_i) - (\sum_{i=1}^n b_i) \log(a_1/b_1),\infty)$, \\
  x_2, & if $x \in (\sum_{i=2}^n b_i\log(a_i/b_i) - (\sum_{i=2}^n b_i) \log(a_2/b_2)$, \nonumber \\
  & $\sum_{i=1}^n b_i\log(a_i/b_i) - (\sum_{i=1}^n b_i)\log(a_1/b_1))$, \\
  & $\vdots$ \nonumber \\
  x_k, & if $x \in (\sum_{i=k}^n b_i\log(a_i/b_i) - (\sum_{i=k}^n b_i) \log(a_k/b_k)$, \nonumber \\
  & $\sum_{i=k-1}^n b_i\log(a_i/b_i) - (\sum_{i=k-1}^n b_i)\log(a_{k-1}/b_{k-1}))$, \\
  & $\vdots$ \nonumber \\
  x_n, & if $x \in (0, \sum_{i=n-1}^n b_i\log(a_i/b_i) - (\sum_{i=n-1}^n b_i) \log(a_n/b_n))$.
\end{numcases}
\restorenumcases
Some text after. And an equation after
\begin{equation}
  f(x) = ax^2 + bx + c.
\end{equation}

\end{document}

One would have to update \setupnumcases in order to have a different numbering to a differing numcases.

2

Like this?

enter image description here

Considering comments to question, the code employ empheq package and also environment multlined from package mathtools, which is called by empheq:

\documentclass{article}
\usepackage[a4paper,margin=1in]{geometry}
\usepackage{empheq}

\begin{document}
 \begin{empheq}[left={f(x)=}\empheqlbrace]{align}
x_1,    & \text{ if } x\in
        \Biggl(\sum_{i=1}^n b_i\log(a_i/b_i)-
            \left(\sum_{i=1}^n b_i\right) \log(a_1/b_1),\infty
        \Biggr),                 \tag{C\textsubscript{1}}        \\
x_2,    & \begin{multlined}[t][0.6\textwidth]
            \text{ if } x\in 
        \Biggl(\sum_{i=2}^n b_i\log(a_i/b_i) - \sum_{i=2}^n b_i \log(a_2/b_2), \\
              \sum_{i=1}^n b_i\log(a_i/b_i) -
            \left(\sum_{i=1}^n b_i\right) \log(a_1/b_1)
        \Biggr),
        \end{multlined}
                                \tag{C\textsubscript{2}}        \\
        & \vdots                \notag                          \\
x_k,    & \begin{multlined}[t][0.6\textwidth]
            \text{ if } x\in
        \Biggl(\sum_{i=k}^n b_i\log(a_i/b_i)-\sum_{i=k}^n b_i \log(a_k/b_k), \\
            \sum_{i=k-1}^n b_i\log(a_i/b_i) -
            \left(\sum_{i=k-1}^n b_i\right) \log(a_{k-1}/b_{k-1})
        \Biggr),
        \end{multlined}
                                \tag{C\textsubscript{k}}        \\
        & \vdots                \notag                          \\
x_n,    & \text{ if }
        x\in 
        \Biggl(0, \sum_{i=n-1}^n b_i\log(a_i/b_i) -
            \left(\sum_{i=n-1}^n b_i\right) \log(a_n/b_n)
        \Biggr),
                                \tag{C\textsubscript{n}}
\end{empheq}
\end{document}
  • Mathtools does not provide aligned/align (you're using eq numbers), it comes from amsmath. However, if I'm not mistaken, for align I think a modified version of aligned is used, with custom eqn no placement – daleif Jun 21 '16 at 18:09
  • 1
    huh, now I see mistake, I didn't use aligned, which is from amsmath but multlined, which is from mathtools. Thank you for pointed k me this. – Zarko Jun 21 '16 at 18:47

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.