Re: Missing \dddot and \ddddot

[Aditya Mahajan <adityam@umich.edu>]

On Fri, 15 Sep 2006, Hans Hagen wrote:

> Aditya Mahajan wrote:
>> On Thu, 14 Sep 2006, Hans Hagen wrote:
>>
>>
>>> Aditya Mahajan wrote:
>>>
>>>> On Thu, 14 Sep 2006, WN wrote:
>>>>
>>>>
>>>>
>>>>> Hello,
>>>>> I need to use \dddot and \ddddot in one of my documents, does anyone
>>>>> know how to
>>>>> define these math symbols.
>>>>>
>>>>>
>>>> The trouble is that most fonts do not contain these accents.
>>>> amsmath.sty gets over this definition by faking these symbols. It is
>>>> easy to port these definitions to context.
>>>>
>>>> amsmath.sty definition
>>>>
>>>> \newcommand{\dddot}[1]{%
>>>>    {\mathop{#1}\limits^{\vbox to-1.4\ex@{\kern-\tw@\ex@
>>>>     \hbox{\normalfont ...}\vss}}}}
>>>> \newcommand{\ddddot}[1]{%
>>>>    {\mathop{#1}\limits^{\vbox to-1.4\ex@{\kern-\tw@\ex@
>>>>     \hbox{\normalfont....}\vss}}}}
>>>>
>>>>
>>>> Converting to context
>>>>
>>>> %--------------------%<------------------------------------
>>>> \unprotect
>>>>
>>>> % The true copy of amsmath definitions
>>>> \def\amsdddot {\limits^{\vbox to -1.4ex{\kern-2ex\hbox{\the\textfont\z@ ...}\vss}}}
>>>> \def\amsddddot{\limits^{\vbox to -1.4ex{\kern-2ex\hbox{\the\textfont\z@....}\vss}}}
>>>>
>>>> % I do not understand why you need to give negative height
>>>>
>>>>
>>> \setbox\scratchbox{..} \ht\scratchbox0pt \dp\scratchbox-2pt
>>>
>>
>> I was wondering why amstex definition does this, as the 1.4ex depth
>> was too big. Then I realized that it is not 1.4ex but 1.4\ex@ with
>> \ex@ as .2326ex. ughh....the ugly syntax of plain tex...
>>
>> So here is a more reliable reproduction of amstex dddot and ddddot
>>
>> \newdimen\amstexex
>>
>> \amstexex = .2326ex
>>
> what's this funny number based on, somehow related to interlinespace?
>
> one cannot define a measure globally this way, since an ex is font
> dependent,;
>
> \def\amstexex{\dimexpr.08\lineheight\relax}

The latex package amsgen.sty define it more carefully

\newdimen\ex@
\addto@hook\every@math@size{\compute@ex@}
\def\compute@ex@{%
   \begingroup
   \dimen@-\f@size\p@
   \ifdim\dimen@<-20\p@
     \global\ex@ 1.5\p@
   \else
     \advance\dimen@10\p@ \multiply\dimen@\tw@
     \edef\@tempa{\ifdim\dimen@>\z@ -\fi}%
     \dimen@ \ifdim\dimen@<\z@ -\fi \dimen@
     \advance\dimen@-\@m sp % fudge factor
     \vfuzz\p@
     \def\do{\ifdim\dimen@>\z@
       \vfuzz=.97\vfuzz
       \advance\dimen@ -\p@
       \@xp\do \fi}%
     \do
     \dimen@\p@ \advance\dimen@-\vfuzz
     \global\ex@\p@
     \global\advance\ex@ \@tempa\dimen@
   \fi
   \endgroup
}


Aditya