1. To use the xyzVector types in a function you would normally put a using declaration at the top of the function and then use the short typedef name to declare the objects:

       void
       f()
       {
         using numeric::xyzVector_double;

         xyzVector_double r; // Default constructed (uninitialized)
         xyzVector_double s( 0.0 ); // Constructs s = ( 0.0, 0.0, 0.0 )
         xyzVector_double t( 1.0, 2.0, 3.0 ); // Constructs t = ( 1.0, 2.0, 3.0 )

         ...
         t.x() = 1.5; // Elements can be accessed as x(), y(), and z()
       }
       

2. You can also construct a numeric::xyzVector from the address of the first value in a contiguous data structure like an FArray or std::vector:

         xyzVector_double const pos_ij( &position(1,i,j) ); // position(1-3,i,j)
       

   You can use numeric::xyzVector in loops by accessing the elements by index:

         v( i ); // For i = 1, 2, 3   (1-based indexing for xyzVector )
         v[ i ]; // For i = 0, 1, 2   (0-based indexing for xyzVector )