# How to create new counter of equation

How to create a new counter of equation. The new equation is matriz and use other sequence number.

\documentclass[a4paper,10pt]{article}
\usepackage[utf8]{inputenc}

\begin{document}

$$y = x$$

$$y = \frac{1}{x}$$

The of next matriz equation is 1.

\begin{matriz}
y = \sqrt x
\end{matriz}

\end{document}


I need, equation 1 equation 2 matriz 1 matriz 2 equation 3 matriz 3 matriz 4

New counter of matriz.

-

This can be done using a newenvironment and the amsmath to help with the tagging

I have defined the matriz environment in terms of the equation environment, and tagged it with a new counter; you can use \label and \eqref as usual.

\documentclass{article}
\usepackage{amsmath}

\newcounter{matriz}
\newenvironment{matriz}{\refstepcounter{matriz}\equation}{\tag{M\thematriz}\endequation}
\begin{document}

$$y = x$$

$$y = \frac{1}{x}$$

The of next matriz equation is 1. \eqref{test}
\begin{matriz}\label{test}
y = \sqrt x
\end{matriz}

\end{document}

-

# amsmath with more than equation

I'd go a broader approach …

The following codes uses the environment m and its mandatory argument to use any amsmath environment (that introduces displayed math-mode) in combination with the matrix counter.

The etoolbox helps to redefine the macros \print@eqnum and \incr@eqnum. An alternative is given in the commented part of the code.

Without cmhughes’ solution the actual equation environment still uses \print@eqnum with \theequation but \incr@eqnum with matrix.

## Code

\documentclass[a4paper,10pt]{article}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\usepackage{etoolbox}

\newcounter{matrix}
\renewcommand*{\thematrix}{M\arabic{matrix}}

\makeatletter
\def\@equationname{equation}
\newenvironment{m}[1]{%
\def\mymathenvironmenttouse{#1}%
\ifx\mymathenvironmenttouse\@equationname%
\refstepcounter{matrix}%
\else
\patchcmd{\@arrayparboxrestore}{equation}{matrix}{}{}%          doesn't change output?
\patchcmd{\print@eqnum}{equation}{matrix}{}{}%
\patchcmd{\incr@eqnum}{equation}{matrix}{}{}%
%       \def\print@eqnum{\tagform@\thematrix}%                          instead of etoolbox' \pathcmd
%       \def\incr@eqnum{\refstepcounter{matrix}\let\incr@eqnum\@empty}% instead of etoolbox' \pathcmd
\fi
\csname\mymathenvironmenttouse\endcsname%
}{%
\ifx\mymathenvironmenttouse\@equationname%
\tag{\thematrix}%
\fi
\csname end\mymathenvironmenttouse\endcsname%
}
\makeatother
\begin{document}

$$y = x$$

$$y = \frac{1}{x}$$

The of next matriz equation is \ref{eq:M1}.
\begin{m}{equation}
y = \sqrt x \label{eq:M1}
\end{m}

$$y = \frac{1}{x}$$

\begin{m}{align}
y & = \sqrt x \\
z & = y^2
\end{m}

\begin{m}{alignat}{3}
y & = \sqrt x & \quad\text{col2l} & = \text{col2r} & \quad\text{col3l} & = \text{col3r} \\
z & = y^2 & & & &
\end{m}

\begin{m}{equation}
y = \sqrt x
\end{m}
\end{document}


# Sans-amsmath solution (without eqnarray)

## Code

\documentclass[a4paper,10pt]{article}
\usepackage[utf8]{inputenc}

\newcounter{matrix}
\renewcommand*{\thematrix}{M\arabic{matrix}}

\makeatletter
\newenvironment{matriz}{%
\def\@eqnnum{{\normalfont \normalcolor (\thematrix)}}%
\def\equation{\refstepcounter{matrix}}%
\equation%
}{%
\endequation%
}
\makeatother

\begin{document}

$$y = x$$

$$y = \frac{1}{x}$$

The of next matriz equation is \ref{eq:m1}.

\begin{matriz}\label{eq:m1}
y = \sqrt x
\end{matriz}

$$y = x$$

\begin{matriz}
y = \sqrt x
\end{matriz}
\end{document}


## Output

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+1 very nice and general! –  tohecz Nov 26 '12 at 12:29