title: What does the notation T(n) mean?
body: <p>We learned about big O notation, but I often see T(n) as well. For example,</p>
  
  <pre><code>public static Comparable[] mergeSort(Comparable[] A, int low, int high) {
    if (low &lt; high) { //at least 2 elements?                //cost = c
      int mid = (low + high)/2;                             //cost = d
      Comparable[] A1 = mergeSort(A, low, mid);             //cost = T(n/2) + e
      Comparable[] A2 = mergeSort(A, mid+1, high);          //cost = T(n/2) + f
      return merge(A1,A2);                                  //cost = g n + h
    }
    .... //cost = i
  </code></pre>
  
  <p>I believe c,d,e,... are meant to be arbitrarily named constants.</p>
  
  <p>What does T(n/2) mean? also how is T notation related to big O?</p>