I am trying to write a long equation in the documentation of a function in R.
How can I break it into multiple lines? I tried adding \cr into the \deqn environment but the check returned me the following error
LaTeX errors found: ! Misplaced \cr. \tilde {Var} = \cr \sum _{i \in U} \pi i \Bigl ( 1 - \frac {n-1}... l.298 ...{Y}{n}\sum{i\in U} \pi_i^2 \Biggr)^2 }{}
I am writing documentation using roxygen2, but I also tried to add \cr manually to the Rd file and got the same result.
Here is an example of my code without \cr
#' @details
#'
#' \itemize{
#'
#' \item Equation:
#'
#' \deqn{ \tilde{Var} =
#' \sum_{i \in U} \pi_i \Bigl( 1 - \frac{n-1}{n}\pi_i \Bigr)
#' \Biggr( \frac{y_i}{\pi_i} - \frac{Y}{n} \Biggr)^2
#' - \frac{n-1}{n^2} \sum_{i \in U} \Biggl( 2\pi_i^3 - \frac{\pi_i^2}{2}
#' \sum_{j \in U} \pi_j^2 \Biggr)\Biggr( \frac{y_i}{\pi_i} -
#' \frac{Y}{n} \Biggr)^2
#' + \frac{2(n-1)}{n^3} \Biggl( \sum_{i \in U}\pi_i y_i - \frac{Y}
#' {n}\sum_{i\in U} \pi_i^2 \Biggr)^2 }{}
#'
#'}
and with \cr
#' @details
#'
#' \itemize{
#'
#' \item Equation:
#'
#' \deqn{ \tilde{Var} =
#' \sum_{i \in U} \pi_i \Bigl( 1 - \frac{n-1}{n}\pi_i \Bigr)
#' \Biggr( \frac{y_i}{\pi_i} - \frac{Y}{n} \Biggr)^2 \cr
#' - \frac{n-1}{n^2} \sum_{i \in U} \Biggl( 2\pi_i^3 - \frac{\pi_i^2}{2}
#' \sum_{j \in U} \pi_j^2 \Biggr)\Biggr( \frac{y_i}{\pi_i} -
#' \frac{Y}{n} \Biggr)^2 \cr
#' + \frac{2(n-1)}{n^3} \Biggl( \sum_{i \in U}\pi_i y_i - \frac{Y}
#' {n}\sum_{i\in U} \pi_i^2 \Biggr)^2 }{}
#'
#'}