title: how to add up the elements of an array in GPU? any function similar to cublasDasum in CUBLAS?
body: <p>I know I can do the <a href="http://developer.download.nvidia.com/compute/cuda/1.1-Beta/x86_website/projects/reduction/doc/reduction.pdf" rel="nofollow">parallel reduction</a> to sum up the elements of an array in parallel.
  But it is a little difficult for me to follow it. I saw that in cublas, there is this function called <code>cublasDasum</code> that sums up the absolute values of the elements. It seems there should be a very similar function that sums up the elements, not the absolute values. Is there any way I can find the source code of <code>cublasDasum</code> and see how this is done? </p>
  
  <p>Adding up an array is such a basic operation. I can't believe that there is no such a function that does it ... .</p>