Include Iverson Bracket in R documentation -

i wanting include iverson bracket in r documentation (unless there's better way represent information; i'm no mathematician). looks this.

here have valid latex code such expression

w_{neg}=\left\{\begin{matrix} 1 & \sum{(x_i^{n})}>0 \\  0 & \sum{(x_i^{n}})=0 \end{matrix}\right. 

i tried include code below:

#' w_{neg}=\left\{\begin{matrix} #' 1 & \sum{(x_i^{n})}>0 \\  #' 0 & \sum{(x_i^{n}})=0 #' \end{matrix}\right. 

in details section of roxygen2 produces error seen below when compiling pdf documentation:

creating pdf output latex ... warning: running command '"c:\progra~2\miktex~1.9\miktex\bin\texi2dvi.exe"  --pdf "rd2.tex"  -i "c:/r/r-30~1.1/share/texmf/tex/latex" -i "c:/r/r-30~1.1/share/texmf/bibtex/bst"' had status 1 error : running 'texi2dvi' on 'rd2.tex' failed  latex errors: ! misplaced alignment tab character &. <argument> \left \{\begin {matrix} 1 &                                        \sum {(x_i^{n})}>0 \\ 0 & \sum {(x_i^... l.5566   \sum{(x_i^{n}})=0 \end{matrix}\right.}{}  ! emergency stop. <argument> \left \{\begin {matrix} 1 &                                        \sum {(x_i^{n})}>0 \\ 0 & \sum {(x_i^... l.5566   \sum{(x_i^{n}})=0 \end{matrix}\right.}{}  !  ==> fatal error occurred, no output pdf file produced!  error in running tools::texi2pdf() 

how can include iverson bracket in r documentation (unless there's better way represent in case that's better approach)? note removal of these lines allows package compile.

i utilized following in roxygen2 documentation , worked:

#' \deqn{w_{neg}=\left\{\begin{array}{cc} #' 1 & \sum{(x_i^{n})}>0         \\  #' 0 & \sum{(x_i^{n}})=0 #' \end{array}\right.}