title: how to access np array element according to its last element
body: <p>Actually, I am doing a sequence operation about <code>numpy array</code>, therefore, I want to know how to access <code>a[i]</code> quickly? </p>
  
  <p>(Because I access<code>a[i-1]</code> in the last loop, therefore, in <code>c++</code>, we may simply access <code>a[i]</code> by adding 1 to the address of <code>a[i-1]</code>,but I don't know whether it is possible in numpy. Thanks.</p>