title: Xgboost cox survival time entry
body: <p>In the new implementation of cox ph survival model in xgboost 0.81 how does one specify  start and end time of an event?</p>
  
  <p>Thanks</p>
  
  <p>The R equivalent function would be for example :</p>
  
  <pre class="lang-r prettyprint-override"><code>cph_mod = coxph(Surv(Start, Stop, Status) ~ Age + Sex + SBP, data=data)
  </code></pre>