Mrthfx

In the question typesetting a column vector, a very nice solution was given for typesetting a column vector with an arbitrary number of rows. I am attempting to modify the code to produce row vectors instead of column vectors. I made the "obvious" change, i.e., substituting the & for the \ as indicated by the snippet below:

newcountcolveccount

newcommand*colvec[1]{

        globalcolveccount#1

        begin{pmatrix}

        colvecnext

}

defcolvecnext#1{

        #1

        globaladvancecolveccount-1

        ifnumcolveccount>0

                &

                expandaftercolvecnext

        else

                end{pmatrix}

        fi

}

You have to collect the row beforehand, as doing it inside an array environment is quite difficult, as TeX ends a cell as soon as it sees an &. I prefer to do in with a token register and the count255 scratch counter.

We collect two arguments: the first is the number of entries, the second the first entry, in order to initialize the token register with it. We set the counter to the number of requested element (since we have already collected one, we step it down immediately).

Then we start the recursion; the macro rowvectnexta examines the value of the counter; if it's still greater than 0, it calls rowvecnextb that gathers another argument, stores it into the token register (adding an &) and steps down the counter; otherwise it builds the pmatrix by releasing the contents of the register.

newtoksrowvectoks

newcommand{rowvec}[2]{%

  rowvectoks={#2}count255=#1relax

  advancecount255 by -1

  rowvecnexta}

newcommand{rowvecnexta}{%

  ifnumcount255>0

    expandafterrowvecnextb

  else

    begin{pmatrix}therowvectoksend{pmatrix}

  fi}

newcommandrowvecnextb[1]{%

    rowvectoks=expandafter{therowvectoks&#1}%

    advancecount255 by -1

    rowvecnexta}

It shouldn't be a big limitation the fact that you need at least one element:

rowvec{1}{a}

rowvec{2}{a}{b}

rowvec{3}{a}{b}{c}

Notice: usepackage{amsmath} is required. So a minimal example might be the following.

documentclass{article}

usepackage{amsmath}



newtoksrowvectoks

newcommand{rowvec}[2]{%

  rowvectoks={#2}count255=#1relax

  advancecount255 by -1

  rowvecnexta}

newcommand{rowvecnexta}{%

  ifnumcount255>0

    expandafterrowvecnextb

  else

    begin{pmatrix}therowvectoksend{pmatrix}

  fi}

newcommandrowvecnextb[1]{%

    rowvectoks=expandafter{therowvectoks&#1}%

    advancecount255 by -1

    rowvecnexta}



begin{document}



$rowvec{1}{a}$

$rowvec{2}{a}{b}$

$rowvec{3}{a}{b}{c}$



end{document}

A completely different solution that can be generalized to column vectors uses xparse and LaTeX3.

documentclass{article}

usepackage{amsmath}

usepackage{xparse}

ExplSyntaxOn

NewDocumentCommand{Rowvec}{ O{,} m }

 {

  vector_main:nnnn { p } { & } { #1 } { #2 }

 }

NewDocumentCommand{Colvec}{ O{,} m }

 {

  vector_main:nnnn { p } { \ } { #1 } { #2 }

 }



seq_new:N l__vector_arg_seq

cs_new_protected:Npn vector_main:nnnn #1 #2 #3 #4

 {

  seq_set_split:Nnn l__vector_arg_seq { #3 } { #4 }

  begin{#1matrix}

  seq_use:Nnnn l__vector_arg_seq { #2 } { #2 } { #2 }

  end{#1matrix}

 }

ExplSyntaxOff



begin{document}



$Rowvec{a}Rowvec{a,b}Rowvec[;]{a;b;c}$



$Colvec{a}Colvec{a,b}Colvec[;]{a;b;c}$



end{document}

The optional argument is the delimiter to be used to separate entries in the list given as argument.

It's sufficient to change { p } into { b } in the two main definitions to get brackets instead of parentheses.

Note: this requires expl3 dated September 2012 or later.

I would like to suggest a dirty solution, which I use:

newcommand*{rowvec}[1]{left( #1right)}

The advantage is that its usage is simple: rowvec{a,b,c,d,e}. I can easily imagine that it is not robust... For me it works.

This is an old question... but as it surfaced again let me point out that one can do these things without token register or macro storage or count registers.

documentclass{article}

usepackage{amsmath}

makeatletter

% USAGE Matrix { a,..,z; A,.., Z ; ... ; aA, ..., zZ}

% NO semi-colon for the last row.

newcommand{Matrix}[1]

    {begin{pmatrix}

      Matrix@r #1;@bye;Matrix@r

     end{pmatrix}}



defMatrix@r #1;{@bye #1Matrix@z@byeMatrix@s #1,@bye, }%

defMatrix@s #1,{#1Matrix@t }%

defMatrix@t #1,{@bye #1Matrix@y@bye@firstofone {&#1}Matrix@t}%

defMatrix@y #1Matrix@t{\ Matrix@r }%

defMatrix@z #1Matrix@r {}

def@bye  #1@bye   {}% (the idea of @bye is from xint code)



makeatother



begin{document}thispagestyle{empty}





[ Matrix { a, b  , c , d ; e ,f , 3, 5; 8, -1, x, y }]



[ Matrix { abc , mathrm{XYZ}; 7, 913; alpha, beta }] 



end{document}

This is an extension to row vectors of my suggestion for column vectors, see here. The idea is to use a similar plain TeX mechanism, and separate the entries with a pipe. Again, the interface with parentheses is the same as used by PSTricks.
The code is:

defcoords(#1,#2){!left({textstyle#1coords@i#2,,}right)}

defcoords@i#1,{if,#1,else|{#1}expandaftercoords@ifi}

and a MWE would be:

documentclass[margin=2pt]{standalone}



makeatletter

defcoords(#1,#2){!left({textstyle#1coords@i#2,,}right)}

defcoords@i#1,{if,#1,else|{#1}expandaftercoords@ifi}

makeatother



begin{document}

$Pcoords(-3,+4,frac51)$

end{document}

Because the macros make use of the @i notation the code will have to be placed inside at makeatletter - makeatother wrapping before document begins.