I use the following command to write my matrix variables


Thus #1 is the matrix variable, #2 is the superscript and #3 is the subscript. For example \mymat{A}{T}{i} would yield the output $\mathbf{A}^{T}_{i}$. Most often, the case is that I don't need the subscript and superscript arguments and I end up writing \mymat{A}{}{}. Is there a way to make the last two brackets optional?

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    twoopt, from the oberdiek bundle`, does that. – Bernard Oct 28 '14 at 7:37
  • Yes but it's almost always a bad choice of input syntax (not a technical point, of course). – Joseph Wright Oct 28 '14 at 7:45
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    \newcommand{\mymat}[1]{\mathbf{#1}} and \mymat{A}^{T}_{i} is clearer and not more difficult to type. – egreg Oct 28 '14 at 8:15
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    Note that ^{} and _{} affect the spacing so it is better to use a markup that does not put in null sub and superscript atoms. – David Carlisle Oct 28 '14 at 11:00

You could use the xparse package which offers great possibilities for defining user commands:

My First attempt:

\DeclareDocumentCommand{\mymat}{o m o}  

Egregs simpler solution with IfValueT

\DeclareDocumentCommand{\mymat}{o m o}  

m stands for mandatory argument, o for optional.

IfValueT{argument}{true code} checks if the argument was given and calls either true code or does nothing.

IfNoValueTF{argument}{true code}{false code} checks if the argument was not given and calls either {true code} or {false code}

Result (You should maybe add a negative math space \! if you have an A matrix.: \mymat{A}[\!\top]):


enter image description here

| improve this answer | |
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    Simpler: \mathbf{#2}\IfValueT{#1}{_{#1}}\IfValueT{#3}{^{#3}} – egreg Oct 28 '14 at 12:44
  • Of course! Will edit my answer – MaxNoe Oct 28 '14 at 12:45
  • @MaxNoe I suggest to keep both versions, to show different approaches. – egreg Oct 28 '14 at 12:49
  • Ok. Now we have both. – MaxNoe Oct 28 '14 at 12:59
  • @egreg \mathbf{#1}\IfValueT{#2}{_{#2}}\IfValueT{#3}{^{#3}} is this correct? – dineshdileep Oct 31 '14 at 4:32

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