[texhax] please help with latex

[Axel E. Retif]

On  18 Sep, 2009, at 07:11, monika hardy wrote:

> A friend is using latex and having trouble – here is his letter-
>
> Hello, I am having problems with the following bit of code. when I
> compile the document, LaTeX complains that \SI is an undefined control
> sequence and points to the line above \end{equation*}. I have been
> unable to pinpoint the source of the problem, and would be gratefull  
> for
> any assistance.
>
> \begin{equation*}
> c_\text{Al} = \frac{\SI{0,150}{\kilo\gram}\cdot
> \SI{4180}{\joule\per\kilo\gram\per\kelvin} \cdot
> (\SI{25,2}{\celsius} - \SI{23,5}{\celsius})} {\SI{0,018}{\kilo\gram}) 
> \cdot
> (\SI{100}{\celsius} - \SI{25,2}{\celsius})}
> \end{equation*}

For me, this typesets fine:

\documentclass{article}
\usepackage{siunitx}
\usepackage{amsmath}
\begin{document}
\begin{equation*}
c_\text{Al} = \frac{\SI{0,150}{\kilo\gram}\cdot
\SI{4180}{\joule\per\kilo\gram\per\kelvin} \cdot
(\SI{25,2}{\celsius} - \SI{23,5}{\celsius})} {\SI{0,018}{\kilo\gram}) 
\cdot
(\SI{100}{\celsius} - \SI{25,2}{\celsius})}
\end{equation*}
\end{document}

Best,

Axel