Math & Science ⇒ the equation number

[mathselpi]

hi!
I want to make that the example below

... (2.1)

... (2.2)

... (3.1)

... (3.2)

etc.

[gmedina]

Which document class are you using? From the title of the thread, you are talking about the counter for equations, right? In (2.1) the "2" represents the number of the current chapter, section? and I guess that the "1" will represent the first equation inside that sectional unit. Is that correct?

Please try to describe your requests more explicitly, and including all the relevant information.

[mathselpi]

Code: Select all

\documentclass[12pt,a4paper,oneside]{report}
\usepackage{graphicx}
\usepackage{amsmath}
\begin{document}
\renewcommand{\theequation}{1.\arabic{equation}}
\begin{eqnarray}
a
\end{eqnarray}
\begin{eqnarray}
b
\end{eqnarray}
\renewcommand{\theequation}{2.\arabic{equation}}
\begin{eqnarray}
c
\end{eqnarray}
\begin{eqnarray}
d
\end{eqnarray}

\end{document} 

I want to make
c (2.1)

d (2.2)

instead of

c (2.3)

d (2.4)

thanks

[gmedina]

Simply reset the counter:

Code: Select all

\documentclass[12pt,a4paper,oneside]{report}
\usepackage{graphicx}
\usepackage{amsmath}
\begin{document}
\renewcommand{\theequation}{1.\arabic{equation}}
\begin{align}
a
\end{align}
\begin{align}
b
\end{align}
\renewcommand{\theequation}{2.\arabic{equation}}
\setcounter{equation}{0}
\begin{align}
c
\end{align}
\begin{align}
d
\end{align}

\end{document}

eqnarray shouldn't be used anymore: Avoid eqnarray!

[mathselpi]

thank you very much