Argthtjtr

I'm attempting to create a multiline equation with some characters than span both lines.

I've come closer by using the amsmath package

begin{multline*}

Pr[Xleftarrow DECODE(Delta;r_1,...,r_ell) | 

displaystyle{(Delta;q_1,...,q_ell)leftarrow QUERY(1^lambda;J)} \

displaystyle{Lambda (Lambda^ell _{j=1})}

]

end{multline*}

But I'm at a loss as this does not allow me to span some characters on both lines

Any suggestions would be appreciated.

My main suggestions are (a) use biggl[, biggm|, and biggr] to structure the equation and (b) use a two-row array environment for the material between biggm| and biggr]. I wouldn't use a multline* environment, though. An unnumbered single-line display math environment does fine.

documentclass{article}

usepackage{amsmath}

usepackage{array}   % for 'newcolumntype' macro

newcolumntype{L}{>{displaystyle}l} % automatic displaystyle math mode

begin{document}

[

Prbiggl[

Xleftarrow mathit{DECODE}(Delta;r_1,dots,r_ell) 

biggm| 

begin{array}{@{}L@{}}

   (Delta;q_1,dots,q_ell)leftarrow mathit{QUERY}(1^lambda;J) \

   Lambda bigl(Lambda^ell_{j=1}leftarrow mathit{RESPOND}(X^{(j)};q_j)bigr)

end{array}

biggr]

]

end{document} 

The image has several inconsistencies in the typesetting.

I suggest to define semantic commands in order to be sure that similar objects are always typeset the same.

I don't like ell, but you can use it in place of the plain l.

documentclass{article}

usepackage{amsmath}



newcommand{func}[1]{mathit{#1}}



begin{document}



begin{equation*}

Prleft[

  X gets func{DECODE}(Delta;r_1,dots,r_l)

;middle|;

  begin{matrix}

  (Delta;q_1,dots,q_l) gets func{QUERY}(1^lambda;J) \

  Lambda(Lambda_{j=1}^l gets func{RESPOND}(X^{(j)};q_j))

  end{matrix}

right]

end{equation*}



end{document}

A slightly different approach, where you specify the brackets as inherently attached to Pr and can choose their size (see the documentation of DeclarePairedDelimiter in mathtools). Basically, Pr* selects automatic size, Pr[big] (or any other delimiter size changing command in the optional argument) selects the stated size.

documentclass{article}

usepackage{amsmath,mathtools}



newcommand{func}[1]{mathit{#1}}



renewcommand{Pr}{operatorname{Pr}brackets}

DeclarePairedDelimiterX{brackets}[1]{[}{]}{#1}

newcommand{given}{;delimsize|;mathopen{}}



begin{document}



begin{equation*}

Pr*{

  X gets func{DECODE}(Delta;r_1,dots,r_l)

given

  begin{matrix}

  (Delta;q_1,dots,q_l) gets func{QUERY}(1^lambda;J) \

  Lambda(Lambda_{j=1}^l gets func{RESPOND}(X^{(j)};q_j))

  end{matrix}

}

end{equation*}



begin{equation*}

Pr[Big]{

  X gets func{DECODE}(Delta;r_1,dots,r_l)

given

  begin{matrix}

  (Delta;q_1,dots,q_l) gets func{QUERY}(1^lambda;J) \

  Lambda(Lambda_{j=1}^l gets func{RESPOND}(X^{(j)};q_j))

  end{matrix}

}

end{equation*}



begin{equation*}

Pr[bigg]{

  X gets func{DECODE}(Delta;r_1,dots,r_l)

given

  begin{matrix}

  (Delta;q_1,dots,q_l) gets func{QUERY}(1^lambda;J) \

  Lambda(Lambda_{j=1}^l gets func{RESPOND}(X^{(j)};q_j))

  end{matrix}

}

end{equation*}



end{document}

by use of array:

documentclass{article}

usepackage{amsmath}



begin{document}

[

Pr left[Xleftarrowtext{DECODE}(Delta;r_1,dotsc,r_ell) middle|

    begin{array}{l}

    (Delta;q_1,dotsc,q_ell)leftarrow text{QUERY}(1^lambda;J) \

     Lambda(Lambda^ell _{j=1}) leftarrowtext{RESPOND}(X^{(j)}:q_j)

     end{array}

    right]

]

end{document}