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I am totally new to LaTeX (use it for 2 days), so I am sorry if this has already been asked, but I spent the last 6 hours searching for a solution, but to no avail. (I stumbled upon a package xpeek which might be able to do what I want (or maybe not), but the documentation was way to complex for me to get anything out of it.)

I am using the ansmath package to write some formulas. I want to introduce a new command for formating my matrix variables. My first attempt was:


which looks fine, except when I use subscripting. In this case, my lower indices are too far away to look nice. E.g. $\mtrx{P}_{\mu\nu}$ Because P is in italics, the space between the P and the subscript is disturbingly large. Using $\mtrx{P\!}_{\mu\nu}$ looks fine, but I get into trouble when using a superscript too: In $\mtrx{P\!}_{\mu\nu}^{*}$, the * is way too close, and in $\mtrx{P}_{\mu\nu}^{*}$ the space between P and \mu is too large.

So, my desired behaviour is to write my macro \mtrx in a way, that it has a look at the tokens after the macro. If there is a subscript present, it inserts a \! after the #1. If there is a subscript and a superscript, it inserts a \; in the superscript. If there is no subscript nothing is changed.

I tried a bit with


but was not able to detect if there is also a superscript present - or at all how to read past the first character after the macro. I guess, this should somehow be possible with \@car and \@cdr, but I have no real clue on how to use them.

Any help is appreciated. Thank you for your time.


Ok, finally I found a solution. I stumbled upon a version of \@ifnextchar which removes the character in case of a match here. I have no clue how it works, but it works.

By using it to remove the _ and ^ characters, I was able to call some other macros turning A_{B} into something like \@mtrx@sub{A}{B}.

Just in case, someone is searching for a similar problem, here is my solution.

  1. \removeifnextchar is taken from the link above and acts similar to \@ifnextchar, except it removes the character on match.
  2. \mtrx only formates its argument into bold face and calls \@mtrx@chk to check for sub- and superscripts
  3. \@mtrx@chk peeks the next character using \removeifnextchar and calls \@mtrxsub or \@mtrx@sup, respectively, or returns its argument in case the next character is neither _ nor ^.
  4. \@mtrx@sub and \@mtrx@sup take 2 arguments each, attach them in subscript or superscript fashion and call \@mtrx@chk again with this new argument in order to evaluate the next sub- or superscript.

Maybe this is not the best solution, but I am really glad that I finally found it. Anyway, in order to learn from this, please feel free to comment and/or improve.

      \let\scratch= %

    \removeifnextchar{_} %
    { \removeifnextchar{^} %
share|improve this question
Well, the spacing does not look so bad in my opinion. Also, if you were to implement that particular command, it would not work so well with, say, A instead of P. But if you really want to, you could use a macro with 2 arguments like so : \boldsymbol{#1}_{\!#2}. I think it is a little bit awkward, but maybe it can help. – zuggg Jun 19 '13 at 5:27
You seem to be a fast learner after only two days with LaTeX! impressive... – jfbu Jun 19 '13 at 6:59
Thank you for the compliment ^__^. – Ineluki Jun 19 '13 at 7:07
up vote 2 down vote accepted

\boldsymbol internally boxes the character and sets it in a new math list. This prevents the font-specified subscript correction being applied. If instead you use the alternative mechanism in the bm package the P is set as a bold letter in the current math list and then TeX will correct the subscript position by an amount set in the font parameters for the font being used:

enter image description here






share|improve this answer
Thanks! This really helps a lot. Using this approach there is no need to worry about matrices like "R" which seem to connect with my indices. And the solution is a lot easier, too. – Ineluki Jun 20 '13 at 16:06

Something like this:


\def\mtrx #1{\ilktoks{\mtrx@a{#1}}\@ifnextchar_{\mtrx@A}%

\def\mtrx@A _#1{\ilktoks\expandafter {\the\ilktoks_{#1}}%

\def\mtrx@B ^#1{\ilktoks\expandafter {\the\ilktoks^{\mtrx@sup #1}}%

\def\mtrx@AB ^#1{\ilktoks\expandafter{\the\ilktoks^{\;#1}}\mtrx@endsubsup }

\def\mtrx@BA _#1{\ilktoks\expandafter{\the\ilktoks_{#1}}\mtrx@endsubsup }

\def\mtrx@end    {\def\mtrx@a ##1{\boldsymbol{##1}}\the\ilktoks }

\def\mtrx@endsub {\def\mtrx@a ##1{{\boldsymbol{##1}\!}}\the\ilktoks }

\def\mtrx@endsup {\def\mtrx@a ##1{{\boldsymbol{##1}}}\def\mtrx@sup {}%
                  \the\ilktoks }

\def\mtrx@endsubsup {\def\mtrx@a ##1{{\boldsymbol{##1}\!}}%
                     \def\mtrx@sup {\;}\the\ilktoks }


$\mtrx {P}Q$ (with \string\mtrx)

$\boldsymbol{P}Q$ (without)

$\mtrx {P}_{\mu\nu}Q$ (with \string\mtrx)

${\boldsymbol{P}}_{\mu\nu}Q$ (without)

$\mtrx {P}^{*}Q$ (with \string\mtrx)

${\boldsymbol{P}}^{*}Q$ (without)

$\mtrx {P}_{\mu\nu}^{*}Q$ (with \string\mtrx; sub first)

${\boldsymbol{P}}_{\mu\nu}^{*}Q$ (without)

$\mtrx {P}^{*}_{\mu\nu}Q$ (with \string\mtrx; sup first)

${\boldsymbol{P}}^{*}_{\mu\nu}Q$ (without)



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