Math & Science ⇒ Formula Conditional

[ArataFan]

Sorry everyone, but I tried to search many sites but no result. I want to write equation like the attached one.

Thanks so much

[localghost]

The first equation is nothing special and can be typeset as usual in an {equation} environment. The second one would need the empheq package for the brace on the left side.


Best regards and welcome to the board
Thorsten

[ArataFan]

Many thanks for your help, you are very kind to me. But I still can't solve my problem.

I used {equation} environment like this:

Code: Select all

\begin{equation}
Th(flow1) = Th(flow2) =  G, if G < \frac{B}{3}
\end{equation}

And the result is displayed as formula (3.1)

The second one need the empheq package but I dont know how to install additional package in LateX, I searched in wiki, but I dont understand.

Moreover, I'm using LateX in windows7, when I want to extract file to .pdf, I must write text in .txt document, then I type "platex filename.txt", then "dvipdfmx filename.dvi" in C command. This is so difficult to check .pdf file before they become finished.

Please help me, thank you!

[cgnieder]

If you have pieces of text in an equation you should use amsmath's \text{} macro to mark them correspondingly:

Code: Select all

% preamble:
% \usepackage{amsmath}
\begin{equation}
 Th(\text{flow1}) = Th(\text{flow2}) =  G, \text{ if } G < \frac{B}{3}
\end{equation}

(I don't actually know if »flow1« and »flow2« should be text here. They looked like it...)

Regards

[Stefan Kottwitz]

I guess at least the amsmath package is installed on your computer, since this is standard for good math typesetting.

A personal opinion first, I would write Th and flow1 in upright letters, since italic letters are used for variables, operators and text commonly upright. Definign a macro or an operator would be convenient. So my text would be

Code: Select all

\documentclass{article}
\usepackage{amsmath}
\DeclareMathOperator{\Th}{Th}
\DeclareMathOperator{\flow}{flow}
\begin{document}
\begin{equation}
  \Th(\flow_1) = \Th(\flow_2) =  G, \text{ if } G < \frac{B}{3}
\end{equation}
\end{document}

The brace before the equation could be done without empheq, with \left\{ and \right. and an aligned environment (of amsmath):

Code: Select all

\documentclass{article}
\usepackage{amsmath}
\DeclareMathOperator{\Th}{Th}
\DeclareMathOperator{\flow}{flow}
\begin{document}
\begin{equation}
  \left\{
  \begin{aligned}
    \Th(\flow_1) &=  G \\
    \Th(\flow_2) &= \ldots
  \end{aligned}
  \right.
\end{equation}
\end{document}

equation.png (2.27 KiB) Viewed 29121 times

Stefan

[ArataFan]

Thank you very much for your help, I solved my problem.

First opinion, I know the {equation} environment but the most thing I want here is the space between , and if. This is my code:

Code: Select all

\begin{equation}
Th(\text{flow1}) = Th(\text{flow2}) = G, \:\:\:\:\:\:\:\text{if} \:\:\:G < \frac{B}{3}
\end{equation}

The result is shown as attached formula (3.1)

Second opinion, special thanks to Stefan_K for teaching me aligned environment. Here is my code:

Code: Select all

\begin{equation}
\left\{
\begin{aligned}
Th(\text{flow1}) &= G \\
Th(\text{flow2}) &= \dfrac{B-G}{2} 
\end{aligned}
\right.
\:\:\:\:\:\text{if} \:\:\:\dfrac{B}{3} \leq G < B_1 - B_2
\end{equation}

The result is shown as the attached formula (3.2)

Moreover, my PC can't run this command \DeclareMathOperator but it's ok

[localghost]

[…] The second one need the empheq package but I dont know how to install additional package in LateX, I searched in wiki, but I dont understand. […]

This is a bit fuzzy. Therefore some questions.

• What did you try to install the package? Package installation is usually by the package manager of your TeX distribution. What exactly does not work?
• Which wiki do you mean? A TeX distribution usually has a manual where its handling is explained. What exactly did you not understand?

Precise answers to these questions would be very helpful.

[ArataFan]

First, I downloaded full .dtx file in this site: http://ctan.org/tex-archive/macros/latex/contrib/mh
Then, I read how to install .dtx package in this site: http://en.wikibooks.org/wiki/LaTeX/Inst ... a_Packages
I couldn't install, so when I type

Code: Select all

    \documentclass{article}
    \usepackage{empheq}
    \begin{document}
    \begin{equation}
      Th(flow1) = Th(flow2) =  G, \text{ if } G < \frac{B}{3}
    \end{equation}
    \end{document}

Last, I type "platex fiename.txt" in C command, and this is the result:

LaTeX Error: File 'empheq.sty' not found.

[localghost]

First, I downloaded full .dtx file in this site: http://ctan.org/tex-archive/macros/latex/contrib/mh
Then, I read how to install .dtx package in this site: http://en.wikibooks.org/wiki/LaTeX/Inst ... a_Packages
I couldn't install […]

So I ask once again: Why don't you just use the package manager of your TeX distribution to install packages?

[ArataFan]

So I ask once again: Why don't you just use the package manager of your TeX distribution to install packages?

Sorry, I don't know how to use the package manager of TeX, this is the most important thing I want to tell. Can you teach me how to use this one?