[texhax] amstex question

[Philip G. Ratcliffe]

> I am trying to align four long lines of formula, 
> [snip]
> 
> Here is my tex source;  I include definitions of my commands 
> being used
> **************************************************************
> ***************************************
> \newcommand{\pddat}[3]{\frac{\partial#1}{\partial#2}\left(#3\right)}
> \newcommand{\delx}{\triangle x}
> \newcommand{\dely}{\triangle y}
> \begin{equation*}
> \begin{split}
> \fof{x+\delx,y+\dely}-\biggl(\fof{x,y}\right.   <===!!!
> &+\left.\pddat{f}{x}{x,y}\delx
> +\pddat{f}{y}{x,y}\dely\right)\\
> =\biggl(\fof{x+\delx,y+\dely}-\fof{x,y}\biggr)
> &-\left(\pddat{f}{x}{x,y}\delx
> +\pddat{f}{y}{x,y}\dely\right)\\
> =\left(\pddat{f}{x}{x+\delts{1},y+\dely}\delx
> +\pddat{f}{y}{x,y+\delts{2}}\dely\right)
> &-\left(\pddat{f}{x}{x,y}\delx
> +\pddat{f}{y}{x,y}\dely\right)\\
> =\left(\pddat{f}{x}{x+\delts{1},y+\dely}-\pddat{f}{x}{x,y}\right)\delx
> &+\left(\pddat{f}{y}{x,y+\delts{2}}-\pddat{f}{y}{x,y}\right)\dely.
> \end{split}
> \end{equation*}

The very first "\right." (indicated <===!!!) above is unpaired.  You can't
match it with "\biggl("; you must match "\left" with "\right".  Just use
"\bigg(" for the preceding parenthesis and drop the "\right." altogether.

Cheers,  Phil