title: Legend with matplot
body: <p>rOU is a matrix of 3 columns and 250 rows and the following graph</p>
  
  <p>matplot(rOU,type="l", ylim=range(rOU), col=c("black","green","red")</p>
  
  <p>How can i write the legend in R for each columns of rOU?</p>
  
  <p>Thank you.</p>