# [texhax] 3x3 array of alighned equations

Novak Elliott N.S.J.Elliott at warwick.ac.uk
Thu Nov 10 11:53:55 CET 2005

Philip, I saw your post appear right I hit the send button - great minds think alike!
Novak.

>>> "Novak Elliott" <N.S.J.Elliott at warwick.ac.uk> 11/09/05 03:06pm >>>
I've figured out a work-around solution: simply wrap the whole thing up in a subequations environment and put a \label after the \begin{subequations} and before \begin{alignat}.  This also eliminates the need for the stepcounter command.

Here is the real set of equations that I wanted to display all along, copy and paste the code for quite a nice bit of texing!

\begin{subequations}
\label{eqn:strains}
\begin{alignat}{3}
\epsilon_{xx} & = \frac{\partial u}{\partial x},&
\epsilon_{yy} & = \frac{\partial v}{\partial y},&
\epsilon_{zz} & = \frac{\partial w}{\partial z},\tag{\theequation a,b,c}\\
\epsilon_{yz} & = \frac{\partial w}{\partial y} + \frac{\partial v}{\partial z},&
\epsilon_{zx} & = \frac{\partial u}{\partial z} + \frac{\partial w}{\partial x},&
\epsilon_{xy} & = \frac{\partial v}{\partial x} + \frac{\partial u}{\partial y},\tag{\theequation d,e,f}\\
2\bar{\omega}_x & = \frac{\partial w}{\partial y} - \frac{\partial v}{\partial z},&
\quad 2\bar{\omega}_y & = \frac{\partial u}{\partial z} - \frac{\partial w}{\partial x},&
\quad 2\bar{\omega}_z & = \frac{\partial v}{\partial x} - \frac{\partial u}{\partial y}.\tag{\theequation g,h,i}
\end{alignat}
\end{subequations}

The individual equations may be referred to by \ref{eqn:strains}a, \ref{eqn:strains}b, etc.

So the subequations environment was only used to gain access to the overall equation number, while the tags are made manually using the \tag command, which I think is a reasonable solution.  The overall equation number may change if the document was reordered but it is unlikely that the order of the subequations would ever change so referencing via \ref{mainequationlabel}a would be in keeping with the tex spirit!

cheers,
Novak