4

I want to write the text (1st case) on the middle right of this two equation, any idea for this? Thank you. 

      \begin{eqnarray*}
        % \nonumber % Remove numbering (before each equation)
          \tau_{h}^{*}(x^{*}) &=& \frac{-(1 - \lambda V^{*\infty}\tau_{h,in}^{*})x^{*} + (1 + V^{*\infty}\tau_{h,in}^{*})}{(1 + \lambda)V^{*\infty}} \\
          \tau_{c}^{*}(x^{*}) &=& (\frac{1}{1 + \gamma})\{1 - \gamma \tau_{h,in}^{*} - \frac{\gamma}{(1 + \lambda) V^{*\infty}}\} x^{*} + (\frac{1}{1 + \lambda})(\frac{1}{V^{*\infty}} + \tau_{h,in}^{*}) \qquad   \text{(First case)}
        \end{eqnarray*}

enter image description here

Sango
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Mohamed Hasnaoui
  • 135
  • 7
  • 1
    Can some of these answers may be the solution? https://tex.stackexchange.com/questions/402902/independent-text-in-between-aligned-eqnarray – Sango Jan 31 '20 at 14:53
  • @Sango - I wouldn't say that the answers in the link you provided solve the OP's question. The OP wants to place a string -- here: "First case" -- to the right of the two equations. In contrast, the main answer in your linked posting shows how to place text left-aligned and between the rows. – Mico Jan 31 '20 at 15:10

3 Answers3

6

Don't use eqnarray or eqnarray*. See the posting eqnarray vs align for an in-depth discussion of this issue.

Use one of the multi-line equation environments of the amsmath package instead. For the case at hand, I suggest you employ a split environment. The amsmath package provides the instruction \tag; it would appear to meet your typesetting requirement perfectly.

While you're at it, you may also want to increase the sizes of the round parentheses and curly braces in the second row.

enter image description here

\documentclass{article}
\usepackage[letterpaper,margin=1in]{geometry} % set suitable page parameters
\usepackage{amsmath} % for 'split' env. and '\tag' macro
\begin{document}

\[
\begin{split}
\tau_{h}^{*}(x^{*}) 
&= \frac{-(1 - \lambda V^{*\infty}\tau_{h,in}^{*})x^{*} 
  + (1 + V^{*\infty}\tau_{h,in}^{*})}{(1 + \lambda)V^{*\infty}} \\
\tau_{c}^{*}(x^{*}) 
&= \Bigl(\frac{1}{1 + \gamma}\Bigr)
   \Bigl\{1 - \gamma \tau_{h,in}^{*} 
      - \frac{\gamma}{(1 + \lambda) V^{*\infty}}\Bigr\} x^{*} 
+ \Bigl(\frac{1}{1 + \lambda}\Bigr)
  \Bigl(\frac{1}{V^{*\infty}} + \tau_{h,in}^{*}\Bigr) 
\end{split}
\tag{First case}
\]
\end{document}
Mico
  • 506,678
5

Here are three possibilities, one is based on the empheq package, which loads mathtools, which loads amsmath. I also improved a bit the look of the equations, removing unnecessary parentheses.

    \documentclass{article}
    \usepackage[showframe]{geometry}
    \usepackage{empheq, amssymb}

    \begin{document}

    \begin{alignat*}{2}
        % \nonumber % Remove numbering (before each equation)
          \tau_{h}^{*}(x^{*}) &=\frac{-(1 - \lambda V^{*\infty}\tau_{h,in}^{*})x^{*} + (1 + V^{*\infty}\tau_{h,in}^{*})}{(1 + \lambda)V^{*\infty}} & & \\
    \ArrowBetweenLines*[\text{First case}]
          \tau_{c}^{*}(x^{*}) &=\frac{1}{1 + \gamma}\Bigl(1 - \gamma \tau_{h,in}^{*} - \frac{\gamma}{(1 + \lambda) V^{*\infty}}\Bigr) x^{*} + \frac{1}{1 + \lambda} \Bigl(\frac{1}{V^{*\infty}} + \tau_{h,in}^{*}\Bigr) & &
        \end{alignat*}
    \bigskip

    \begin{empheq}[right=\text{\quad First case}]{align*}
          \tau_{h}^{*}(x^{*}) &=\frac{-(1 - \lambda V^{*\infty}\tau_{h,in}^{*})x^{*} + (1 + V^{*\infty}\tau_{h,in}^{*})}{(1 + \lambda)V^{*\infty}} \\[1ex]
          \tau_{c}^{*}(x^{*}) &=\frac{1}{1 + \gamma}\Bigl(1 - \gamma \tau_{h,in}^{*} - \frac{\gamma}{(1 + \lambda) V^{*\infty}}\Bigr) x^{*} + \frac{1}{1 + \lambda} \Bigl(\frac{1}{V^{*\infty}} + \tau_{h,in}^{*}\Bigr)
    \end{empheq}
    \bigskip

    \begin{equation}\tag*{First case}
      \begin{aligned}
          \tau_{h}^{*}(x^{*}) &=\frac{-(1 - \lambda V^{*\infty}\tau_{h,in}^{*})x^{*} + (1 + V^{*\infty}\tau_{h,in}^{*})}{(1 + \lambda)V^{*\infty}} \\[1ex]
          \tau_{c}^{*}(x^{*}) &=\frac{1}{1 + \gamma}\Bigl(1 - \gamma \tau_{h,in}^{*} - \frac{\gamma}{(1 + \lambda) V^{*\infty}}\Bigr) x^{*} + \frac{1}{1 + \lambda} \Bigl(\frac{1}{V^{*\infty}} + \tau_{h,in}^{*}\Bigr)
    \end{aligned}
    \end{equation}

    \end{document}

enter image description here

Bernard
  • 271,350
2

From -- https://tex.stackexchange.com/a/217524/197451-- is this your requirement

enter image description here

\documentclass{article}

\usepackage{amsmath}

\begin{document}

\noindent Something\dots
\begin{alignat*}{2}
  K_{C} &= \sqrt{EG_{c}} &\qquad &\text{(plane stress)}\\
  \intertext{further description of the equation}
  K_{c} &= \sqrt{\frac{EG_{c}}{1-\nu^{2}}} &&\text{(plane strain)}
\end{alignat*}
Something\dots

\end{document}

OR

another solution with the help of manual raisebox

enter image description here

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{equation}
\label{eq:distrib}
\begin{alignedat}{2}
n_c    &= \max[N \cdot z_{\max} \cdot x, 2 \cdot n_{\min}]
&\quad&\raisebox{-.5\normalbaselineskip}[0pt][0pt]{%
    where $x\sim U([0,1])$%
} \\
n_{co} &= \min[\max[n_c \cdot x, n_{\min}], n_c - n_{\min}] \\
n_{cp} &= n_c - n_{co} \\
n_f    &= N - n_c
\end{alignedat}
\end{equation}

\end{document}

from -- https://tex.stackexchange.com/a/391034/197451

js bibra
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