title: why dopar is not reducing time?
body: <p>I used an example from here 
  <a href="https://cran.r-project.org/web/packages/doParallel/vignettes/gettingstartedParallel.pdf" rel="nofollow noreferrer">https://cran.r-project.org/web/packages/doParallel/vignettes/gettingstartedParallel.pdf</a> </p>
  
  <pre><code>library(doParallel)
  cl &lt;- makeCluster(2)
  registerDoParallel(cl)
  system.time(foreach(i=1:10000) %dopar% sqrt(i))
  system.time(foreach(i=1:10000) %do% sqrt(i))
  stopCluster(cl)
  </code></pre>
  
  <p>This is my output </p>
  
  <pre><code>Loading required package: foreach
  Loading required package: iterators
  Loading required package: parallel
  
  &gt; system.time(foreach(i=1:10000) %dopar% sqrt(i))
     user  system elapsed
    6.307   0.537   7.499
  &gt; system.time(foreach(i=1:10000) %do% sqrt(i))
     user  system elapsed
    4.581   0.035   4.622
  </code></pre>
  
  <p>Why are the timing not reduced with dopar ?</p>