rcpparma_hello_world()
does not return a value, but displays a
message to the console.
rcpparma_outerproduct()
returns a numeric matrix computed as the
outer (vector) product of x
.
rcpparma_innerproduct()
returns a double computer as the inner
(vector) product of x
.
rcpparma_bothproducts()
returns a list with both the outer and
inner products.