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lines 399-429 of file: include/cppad/example/valvector/class.hpp
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   {xrst_begin valvector_element}

   Accessing Elements of a valvector
   #################################
   Returns a reference to the specified element of this valvector.

   Prototype
   *********
   {xrst_literal ,
      // BEGIN_ELEMENT , // END_ELEMENT
      // BEGIN_CONST_ELEMENT , // END_CONST_ELEMENT
   }

   j
   *
   This is the index of the element we are accessing.

   #. If the size this valvector is one, *j* can have any value
      and the return is the single element in this valvector.
   #. If the size of this valvector is not one, *j* must be less than
      its size and the return is the j-th element in this valvector.

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

   {xrst_end valvector_element}