How insert a text on middle right of eqnarray

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*}



• Can some of these answers may be the solution? tex.stackexchange.com/questions/402902/… Jan 31, 2020 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, 2020 at 15:10

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.

\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}

• If you don't want parentheses around "First case", use \tag* instead of \tag.
– Mico
Jan 31, 2020 at 15:06

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

\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

\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{document}


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

\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

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\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{document}

• I may be mistaken, but I thought the OP's objective was to place the text snippet "(First Case)" between the two equation rows.
– Mico
Jan 31, 2020 at 15:00
• right--edit added from @egreg solution with raisebox Jan 31, 2020 at 15:04