Subequations inside a table

I am trying to insert a subequation system inside a table. This is the idea of what I want:

\begin{table*}[tb]
\centering
\caption{Device Modelling Specifications.}
\label{tab:deviceModelling}
%\begin{tabular}{p{2.4cm} p{1.4cm} p{1.4cm} p{1.4cm}}
\begin{tabular}{l c c c}

.....

\hline
\textbf{Fist model} &
\begin{subequations}
$$a = b$$
$$a2 = b2$$
\end{subequations}
&
....


How can I do it?

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Does it mean you're trying to squeeze several equations into a single cell in a table? – Count Zero Jun 30 '12 at 11:38
Please make your code into complete documents (known as MWE) that may be run. equations have to be in p columns or other par-mode contexts as in your commented out line. They may not be in c columns which have to be one line. – David Carlisle Jun 30 '12 at 11:39
We could do with an idea of what you are trying to achieve: this all sounds very odd. – Joseph Wright Jun 30 '12 at 12:03
@CountZero That is right, i have a table, where, in some cells I need to put different equations. – fernando garcía Jun 30 '12 at 12:22
@fernandogarcía please edit your question to be a complete document and then say in what way you need the output to change, so people have a clue how they can help. As I said in my first comment equations should work in p columns but not in c or l columns. – David Carlisle Jun 30 '12 at 13:34

Here is a possible solution:

\documentclass[10pt,a4paper]{article}

\usepackage{amsmath}
\usepackage{array}

\begin{document}
\begin{table*}[tb]
\centering
\caption{Device Modelling Specifications.}
\label{tab:deviceModelling}
\begin{tabular}{|m{2.4cm}|m{1.4cm}|m{1.4cm}|m{1.4cm}|}
\hline
\textbf{Fist model} &
{\begin{align*}
a &= b\\
a2 &= b2
\end{align*}} &
another cell & last cell\\
\hline
dummy & text & I & entered\\
\hline
\end{tabular}
\end{table*}
\end{document}


As David Carlisle put it in his comment, you will need a paragraph type of cell, so l, r or c columns won't do. I assumed you would like to have things centered vertically, so I chose type m (note that this option requires the array package). If you have other preferences, instead of m you can use p (top) or b (bottom).

The amsmath package will give you the possibility to use the align environment, as I did in the example. You can also choose from a wide variety of environments described in the amsmath documentation.

One last thing: The entire align environment is put between curly braces, because otherwise LaTeX will try to expand it at the wrong moment and the document will not compile. This comes from the fact that align uses & to set the alignment points and the same character is used as a cell separator in tabular. Of course in an environment without ampersand (e.g. multline) there is no need for these braces.

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Thanks, it worked :) – fernando garcía Jun 30 '12 at 14:56
I have already vote +, how to validate the answer? – fernando garcía Jun 30 '12 at 15:36
done. Sorry, i had not noticed – fernando garcía Jun 30 '12 at 15:44