Cfrgtkky

I try to use a shortcut for setting matrices with different brackets.
My solution works fine in displaymath and equation environments.
However, as soon as I try to use it within align, there is an error coming up.

Does anyone know a solution where I can still use my definition within align?

documentclass{scrreprt}



usepackage{amsmath}



newcommand{Mtrx}[2][1]{

    ifx0#1

        begin{matrix}  #2 end{matrix}

    elseifx1#1

        begin{bmatrix}  #2 end{bmatrix}

    elseifx2#1

        begin{pmatrix}  #2 end{pmatrix}

    fififi

}



begin{document}

% everything as expected here:

begin{equation}

    Mtrx[2]{A & B \ C & D} = Mtrx[1]{c\d}

end{equation}



% The following align-equation gives an error:

begin{align}

    Mtrx[2]{A & B \ C & D} &= 0

end{align}



end{document}

You solve the issue by simply adding braces in the definition of Mtrx:

newcommand{Mtrx}[2][1]{{% <--- brace

    ifx0#1

        begin{matrix}  #2 end{matrix}

    elseifx1#1

        begin{bmatrix}  #2 end{bmatrix}

    elseifx2#1

        begin{pmatrix}  #2 end{pmatrix}

    fififi

}} % <--- brace

However, here's how I'd do:

documentclass{scrreprt}



usepackage{amsmath}



newcommand{Mtrx}[2]{%

  begin{#1matrix} #2 end{#1matrix}

}



begin{document}



begin{equation}

    Mtrx[p]{A & B \ C & D} = Mtrx[b]{c\d}

end{equation}



begin{align}

    Mtrx[p]{A & B \ C & D} &= 0

end{align}



end{document}

If you really prefer numbers,

documentclass{scrreprt}



usepackage{amsmath}



newcommand{Mtrx}[2][0]{%

  begin{mtrxtype{#1}matrix} #2 end{mtrxtype{#1}matrix}

}

newcommand{mtrxtype}[1]{%

  ifcase#1or bor pfi

}



begin{document}



begin{equation}

    Mtrx[2]{A & B \ C & D} = Mtrx[1]{c\d}

end{equation}



begin{align}

    Mtrx[2]{A & B \ C & D} &= 0

end{align}



end{document}

error is caused by use of ampersands. these from your new command had to be some how hidden from align ones. for example try

begin{align}

{Mtrx[2]{A & B \ C & D}} &= 0

end{align}

or redefine your command as follows:

documentclass{scrreprt}



usepackage{amsmath}



newcommand{Mtrx}[2][1]{

    ifx 0#1

        {begin{matrix}  #2 end{matrix}}

    elseifx 1#1

        {begin{bmatrix}  #2 end{bmatrix}}

    elseifx 2#1

        {begin{pmatrix}  #2 end{pmatrix}}

    fififi

}



begin{document}

% everything as expected here:

begin{equation}

    Mtrx[2]{A & B \ C & D} = Mtrx[1]{c\d}

end{equation}



% The following align-equation gives an error: NOT ANYMORE

begin{align}

    Mtrx[2]{A & B \ C & D} &= 0

end{align}