[texhax] \hline in align environment
Sebastian Canagaratna
s-canagaratna at onu.edu
Mon Jan 5 05:30:39 CET 2009
When discussing elimination of variables in simultaneous equations, it
is usual to have a horzontal line after the two equations which are
being added and subtracted. This appears to be difficult to do in
amsmath align environment. There was a question about this about three
years ago, but there were no satisfactory answers usign align, as far as
I can gather. Here is my solution.
\begin{align*}
4x+ 6y -2z &= -4\\
x -y +2z &= 9\\[-0.2in]
\underline{\phantom{4x+6y-2z}}&\underline{\phantom{y}}\underline{\phantom{-4y}}\\
5x + 5y &= 5\\
x + y &= 1
\end{align*}
I have used underline and for alignment, instead of using \phantom{=} it
is necessary to use \phantom{y} otherwise the lines don't algin
horizontally. Similarly the added y in -4y.
It is because of this alignment problem that the 2nd equation cannot be
directly underlined, as the line from &\phantom{=} will be a little
higher. I guess one might try &\underline{=\phantom{y}}, but I haven't
tried this. If its works, it will be shorter.
I'll be interested in other solutions.
Sebastian Canagaratna
Department of Chemistry and Biochemistry
Ada, Ohio 45810
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