title: Break long formula R documentation
body: <p>I have a long formula that I need to break in the R documentation of a package or it trails off the right hand side of the page.  HEre's the formula in roxygen2 style:</p>
  
  <pre><code>#' \deqn{Cov(r_{ist}, r_{iuv})= [.5\rho_{ist}\rho_{iuv}(\rho_{isu}^2 + 
  #' \rho_{isv}^2 + \rho_{itu}^2 + \rho_{itv}^2) + \rho_{isu}\rho_{itv}+ \newline 
  #' \indent \rho_{isv}\rho_{itu}-(\rho_{ist}\rho_{isu}\rho_{isv} + 
  #' \rho_{its}\rho_{itu}\rho_{itv}) + \rho_{ius}\rho_{iut}\rho_{iuv} + 
  #' \rho_{ivs}\rho_{ivt}\rho_{ivu}]/n_i}
  </code></pre>
  
  <p>Notice I tried to use \new line and indent but this didn't work it still trails off the edge.</p>
  
  <p>How can I break the formula and indent it?  Maybe indenting isn't appropriate (not sure on that).</p>