----------------------------------------------------------------
lines 365-385 of file: include/cppad/example/valvector/class.hpp
----------------------------------------------------------------

   {xrst_begin valvector_sum}

   Sum elements of a valvector
   ###########################
   Returns the sum of the elements in this valvector.

   Prototype
   *********
   {xrst_literal ,
      // BEGIN_SUM , // END_SUM
   }

   {xrst_toc_hidden
      example/valvector/sum.cpp
   }
   Example
   =======
   The file :ref:`valvector_sum.cpp-name` is an example and test of
   valvector sum.

   {xrst_end valvector_sum}