[OS X TeX] Missing $ inserted in a "variations" environment

[Iraj Kalantari]

I am sorry -- Jonathon also explains my remark too!  In my haste, I  
did not read his comprehensive analysis.

Iraj.


On Mar 15, 2009, at 1:10 PM, Iraj Kalantari wrote:

> Setting aside Jonathan's wonderful analysis, if in the minimal  
> example provided
> one replaces the first '\mI' with '$\mI$'
> in the line:
> \m{f(x)} & \bg \mI &  \c \h{\pI} & \bb& \mI & \c & \h{-1} & \d \mI &  
> \bb
> the problem goes away.
>
> Iraj.
>
>
>
>
> On Mar 15, 2009, at 12:39 PM, Jonathan Kew wrote:
>
>> On 15 Mar 2009, at 14:09, <ewan.Delanoy at math.unicaen.fr> <ewan.Delanoy at math.unicaen.fr 
>> > wrote:
>>
>>>                 Hello all,
>>>
>>>
>>> I've just encountered the following problem with TeXShop :
>>
>> You're having a problem with LaTeX, not with TeXShop. It would be  
>> useful to learn something about the distinction.
>>
>>>
>>> 1) Compilation stops with the error message "Missing $ inserted".
>>> 2) If I insist and press "Enter" twice in the console, it eventually
>>> compiles completely
>>> and produces a fine output.
>>
>> Not quite. Look at the first minus-infinity at the bottom; it'll  
>> have a hyphen instead of a minus sign.
>>
>>>
>>> 3) By trial and error, I see that what causes this behaviour is a
>>> "variations" array
>>> (from the variations package) in the middle of my text.
>>> 3) The line number displayed in the error message, l.259, is not  
>>> very
>>> illuminating
>>> because the source text is as follows
>>
>> This is presumably because none of the content of the {variations}  
>> environment actually gets processed until the end reached.
>>
>>>
>>> \noindent \makebox[\textwidth][c]{
>>> \begin{variations}
>>> x  & \mI  &   & \alpha& & & 1 & & \beta&  & & 2 & & \pI & \\
>>> \filet
>>> f'(x) & \bg & + & \bb&  & + & \z & -& \bb & & - &\z& + & &\bd \\
>>> \filet
>>> \m{f(x)} & \bg \mI &  \c \h{\pI} & \bb& \mI & \c & \h{-1} & \d \mI  
>>> & \bb
>>> & \h{\pI}& \d &\frac{3}{2}& \c
>>> & \h{\pI} & \bd \\
>>> \end{variations}
>>> }<- Line 259 is here
>>>
>>> Can anyone help me on this ?
>>
>> One way to locate the problem more precisely, if you don't notice  
>> the incorrect minus sign at first, is to type "i XXXX" in response  
>> to the error message instead of just hitting Enter. You'll see the  
>> inserted XXXX in your output and this may help you spot where  
>> things are going wrong.
>>
>> It seems that {variations} is automatically putting each "cell" of  
>> the table it creates into math mode, probably using an \halign  
>> template. But the \bg command, besides creating an extra rule on  
>> the left, also cancels the alignment template for the current entry  
>> (\show\bg indicates that its expansion  begins with \omit). So  
>> where you have "....& \bg \mI &...." the automatic math mode does  
>> not apply, and hence you get an error when you try to use the  
>> infinity symbol.
>>
>> You can remove the error by adding $...$ around \mI in this case,  
>> but (a) it seems ugly to have to do this, when other cells are  
>> automatically in math mode; and (b) this results in extra space  
>> between the symbol and the following arrow. So it's not really very  
>> satisfactory.
>>
>> It looks like what you should really do is split off the border  
>> you're creating with \bg into a separate column of the table, as  
>> the {variations} environment doesn't know how to combine this  
>> nicely with math-mode content. Thus:
>>
>> 	\noindent \makebox[\textwidth][c]{
>> 	\begin{variations}
>> 	x & & \mI & & \alpha& & & 1 & & \beta& & & 2 & & \pI & \\
>> 	\filet
>> 	f'(x) & \bg & & + & \bb& & + & \z & -& \bb & & - &\z& + & &\bd \\
>> 	\filet
>> 	\m{f(x)} & \bg & \mI & \c \h{\pI} & \bb& \mI & \c & \h{-1} & \d  
>> \mI & \bb
>> 	& \h{\pI}& \d &\frac{3}{2}& \c
>> 	& \h{\pI} & \bd \\
>> 	\end{variations}
>> 	}
>>
>> HTH,  JK
>>
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>
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